Pr Jacques Guyot

Planning policies for language diversity: the weight of national realities in applying international conventions

Never before has "cultural diversity" been such popular topic, not just among international institutions, but also in the field of cultural industries or for the defenders of world cultures. According to Armand Mattelart, who analysed the genesis of "Cultural diversity", it has become a real hotchpotch with, as time goes by, a loss of its meaning and heuristic scope, thus making it difficult to understand the main issues at stake when dealing with the relationships between cultural matters, public policies and economy. [Mattelart, 2005] "Cultural diversity" includes "language diversity" which is similarly subjected to contradictory and paradoxical discourses.

Indeed, as linguistic minorities and researchers already know, the variety of the languages spoken in the world is declining [Crystal, 2000; Hagège, 2000; Moseley, 2010]. The hegemony of two or three international languages (above all the Anglo-Saxon/varieties of English) leading to a language market [Calvet, 2002]; the globalization of media and cultural industries; economic exchanges; and, population flows due to mass tourism and migrations, are some of the majors factors that contribute to marginalizing linguistic idiosyncrasies.

These main trends keep on developing and therefore threaten language diversity, all the more so when minority languages are only spoken within the scope of the private sphere and kept away from media, education, justice and administration.

At the dawn of the XXI century, the awareness that language diversity is a precious heritage is grudgingly be faced by many State authorities throughout the world in planning linguistic policies for minorities. Even though many countries signed the international conventions promoted by the ILO (International Labour organization), UNESCO or the European Union, and sometimes supported these decisions through constitutional changes, concrete measures to promote and foster minority languages usually go unheeded. This is the situation we would like to analyze from a socio-political viewpoint, comparing the case of European and Latin-American countries, on the basis of

inquiries 1 and a critical survey of legal texts in order to point out how national realities are reluctant to go beyond the balance of powers inherited from domination and colonialism. Special attention will be paid to printed and audio visual media; in this particular field, more than constitutional frameworks securing the right to information, what linguistic minorities need to exist within the democratic public sphere is the right to communicate: this challenge is presently becoming a reality in some Latin-American countries like Argentina.

1-Minorities from guardianship to domination.

1-1 What etymology and law tell us about the notion of minority.

For many people, a minority is often defined as a situation of numerical inferiority. It can of course be the case and the UNESCO report gives many examples of such groups composed of a small number of people, generally elderly, and whose future is in great danger. [Moseley, 2010] However, this way of defining a minority is a dead end as it depends on the counting criteria. A linguistic group can be, on the one hand a majority at a regional level and on the other hand a minority when integrated to national census; the Romanis, scattered in many European countries represent more than 10 million people, just like the Kurds who have no state and live in Iraq, Iran, Syria and Turkey; 2 to say nothing about groups that are dominant in one country and become minorities in the next-door country. [Guyot, 2006] Other factors may be determining: insularity keeps small communities from external linguistic influence, the intergeneration transmission rate may be high, even among very small groups of people, Quite often, the reason to focus on numerical inferiority comes from the difficulty to precisely define what a minority is. [Leclerc, 2001] However, in a socio-political perspective, etymology and law give precious clues about the legal status of the "minor", as being a class of individuals put under guardianship and therefore deprived of their freedom of choice and autonomy. In this respect, children are considered as "minors" and under their parents' guardianship until they reach legal majority, a situation nobody would reasonably question in terms of child protection. On the other hand, women and slaves wereand in many countries still aredenied full responsibility, depending respectively on 1 Interviews carried on in 2010 and 2011 in Argentina, Chile, Ecuador and Peru with Mapuche and Quechua community leaders, researchers and educational authorities (Ministry of Education).

2 That is to say, more or less the same number than the Danes or the Catalans.

their husband or masters to lead their lives. The abrogation of such status in order to free oneself from subjection goes through the dynamics of social movements and political resistance. [Guyot, 2006] As far as language communities are concerned, they are also in a position of political inferiority because they are excluded from the public sphere; confined within the private space, language practices have no official character and face different forms of exclusion: tolerated in some media, they have no significant presence in education, a fortiori in administrative forms or procedures. Indeed, most endangered languages owe their fragile existence to the obstinacy of associations and minority groups.

Claims from minorities, particularly those expecting some kind of recognition in the public sphere, are not just a mere cultural issue, but a real political challenge.

In this respect, the theory of domination offers a conceptual framework for a thorough analysis of the stakes related to language planning policies.

1-2 Minority as defined by sociology and political sciences.

As a promoter of a general theory of power where the mechanisms of domination play a central part3 , Pierre Bourdieu stressed the social nature of language, with its relations of symbolic power deeply fixed in a linguistic market unified and dominated by the official tongue. The French sociologist questioned the purely objectivistic and communication-oriented conception of language proposed by Ferdinand de Saussure and more recently Noam Chomsky: indeed, the sociopolitical stakes are a central issue in producing a legitimate language, in a context where this State language becomes the theoretical standard through which all the linguistic practices are objectively measured. [Bourdieu, 1982 : 27] This legitimate language imposed itself through a historical and often conflictual process, subordinating and excluding other idioms or dialects.

For the French sociologist Pierre-Jean Simon, "domination" is also the main feature to describe a minority : The concept of minority [ ] is not associated to less numerous collective wholes but to "dominated" collective wholes. [Simon, 2006 : 155] Therefore, what are important are the different forms taken by the process of domination in order to define a minority as : An ethno-cultural autonomous structured community, being minoritized on the spot or at distance, of variable dimensions, at large or small scale, inside its own national territory, or beyond in different States where its members have lived for generations [ ] in a vulnerable position and who, in spite of internal or external exile, marginalization and oppression, maintain a collective conscience of their identity. [Yacoub, 1998 : 127] In short, being a minority supposes a deliberate action, a policy aimed at marginalizing groups, at keeping their practices or activities within the private area, at denying specific rights in the public sphere (education, administration, justice, media). The expression "minoritized languages" used by the European Bureau of lesser-used languages seems to be appropriate to describe the situation. [Guyot, 2004 : 16] When analyzing the expansion of nationalism described as imagined communities, Benedict Anderson also pointed out the correlation between the emergence of a nation and the choice of a language that exclusively belongs to it, generally drawn from the old tongues in order to build new models around what he calls the vernacular print capitalism. [Anderson, 2002 : 77-78] This is how national languages dominated: since linguistic unity was the keyword in building a national identity, the variety of idioms were doomed to disappear. A "sole and universal language" was the motto that accompanied the commencement of E.U. construction, way before cultural diversity became a political issue in the early 90s.4

The political history of empires and nations also led to the creation of borders, splitting peoples from their former homelands, redistributing them in different national territories or purely seizing their lands. Such geopolitical configurations produced new minorities and had consequences for the way they were taken into account by government authorities. In all cases, members of minorities are secondclass citizens and subalterns.

2-Minorities at the frontiers of socio political marginalization.

There are many degrees in categorizing minorities, between those whose claims may more easily get forms of official recognition and those who are likely to remain in the margins of the public sphere and therefore be condemned to forced integration. Two distinctions can be made that can be applied heuristically to understand the status of minoritized communities.

2-1 Autochthons versus allochthons.

A first line can be drawn between the autochthons or natives, and the allochthons, i.e. the immigrants, nomads or diasporas. Long-established communities stand a better chance to get official rights than populations coming from the outside, like the Maghrebis, Africans, Turks or Indo-Pakistanis who migrate to Europe. Legal texts are quite edifying with a recurrent notion appearing under different terms (national minorities, historic minorities), thus giving more legitimacy to groups that have been living on the national territory for centuries.

This is what a keen supporter of multiculturalism points out when writing that claims to get administrative and/or political rights should be met by government authorities, especially in the case of "national minorities", like "the American Indians, the Bretons or the Catalans". [Kymlicka, 2011] When dealing with the recognition of allochthonous languages rights, national planning policies generally failed to cope with the ever-increasing flows of immigrants over the last 25 years. Indeed, a few countries chose multicultural policies, like Canada with specific measures for the French speakers. However, the recognition of language rights, or the access to media generally left aside the American Indians. This goes to show that one minority can hide another. As for the immigrants, in a general context of international economic crisis and geopolitical conflicts, their desire to integrate into their host country usually drives them to quickly adopt the official language, mainly to find a job, while restricting the use of their mother tongue at home or within their community. Regarding media practices, they usually turn towards the papers and audiovisual networks from their mother countries. [Guyot, 2007] 2-2 Internally colonized versus externally colonized.

A second important dividing line has to do with on the one hand the internally colonized, 5 i.e. the populations speaking a vernacular language who were acculturated in the process of building Nation-States (the Bretons, Catalans, Corsicans or Basques in France; the Frisians in the Netherlands; the Catalans, Galicians and Basques in Spain; or the Welsh and Scots in Great Britain), and on the other hand, the externally colonized, that is to say the peoples conquered by Empires (France, Great Britain, the Netherlands, Portugal, Spain). 6

It really is a matter of socio-historic context. Indeed, in both situations, if the vernacular tongue has been supplanted by the official language imposed by administrative and political authorities, in the first case, the adoption of the dominant culture and language through compulsory education was accompanied by the promise of full access to citizenship: hence the feeling that this acculturation process was occurring of free will. [Giordan, 1992 : 130] On the other hand, the subjects of empires were forced to adopt the colonist's language, most of them remaining totally illiterate and therefore discredited as second-class citizens. The Algerians were for example widely acculturated to the French, but through a segregated school system. As for the peoples stuck in the colonial relations of domination and exploitation, the socio-economic situation often hides the ethnic side and simply cancels out the linguistic issue. This is what happens in South America where the gap between white colonists and natives quickly took place on the basis of racism, discrimination and inequalities of rights. Thus, the return of minority claims works on other mechanisms than in the European countries. For America, the awareness of indianness is what caused the indigenous thought. [Yacoub, 1998 : 65] The effect of domination is far more complex in countries where the indigenous are doubly subalterns, as colonized peoples and as exploited workers. In Bolivia, a country composed of more than 50% of American Indians (Quechua and Aymara), the indigenous always represented an important category, demographically speaking. However, in the period characterized by the union-form, the social question concealed the ethnic issue.

[ Keucheyan, 2010 : 273] This is mainly thanks to large-scale social struggles against inequalities and racism that a policy of equality could be established in Bolivia: demonstrations against the privatization of water in the city of Cochabamba in 2000 prepared the ground for the election of Evo Morales as the president of the Republic. Indeed, as pointed out by the vice-president, one of the most striking features in the social mobilization, through the statements of its spokesmen or in the collective movements of its members when running the blockades, was the symbolic collapse of the prejudice of inequality between the Indians and 6 The Maghrebis or the Africans are a hybrid case since they were first colonized by the French before migrating towards the colonizing country as cheap labour for the industries. They simultaneously hold the two experiences, which even add further to their marginalization.

the Q'aras, between the Aymaras and the Mis'is 7 [ ] The symbolic colonial structure that had accustomed the colonized and colonizers to integrate the idea that the Indians had to address the Q'aras by means of submission, genuflexion and tearful request suddenly exploded under the impulse of a native who no longer feared them and was even saying he could govern them. [García Linera, 2008 : 107-108] Among the symbols of the rebellion, the linguistic claim was one of the main concerns, as a means to exist in the public sphere: using the Aymara or the Quechua to publicly account for the texture, density and advances of the uprising, in the media, the meetings and the debates. [García Linera, 2008 : 109] The split between autochthonous minorities and allochthonous groups coming from immigration, diasporas and nomadism as well as inequalities in principle between internally and externally colonized populations are some of the factors that considerably slowed down the awareness that language cosmopolitanism was neither a divine curse inherited from Babel, nor an obstacle to a common political project.

3-Taking into account language diversity.

The policies intended for promoting language diversity arrived quite late in the agenda of States. Undoubtedly, the 19 th century was the springtime of peoples in Europe.

Nowadays, the issue comes up at a world-wide level and day after day, minorities resurface, says Joseph Yacoub who listed some 7500 ethnic groups and minorities, as well as 6700 languages claiming official recognition of their cultural and linguistic idiosyncrasies. [Yacoub, 1998 : 25-29] Until the end of the 19 th century, the Nation-States as imagined communities built around a unique vernacular language, throwing aside, and sometimes plainly eradicating the other local or regional tongues.

What we are presently witnessing is the revenge of cultures, with a variety of situations according to particular countries and continents. [Mattelart, 1992] Minorities do not exist as such, but are the outcome of the accidents of History.

[ Yacoub, 1998 : 105] Wars, inter-ethnic conflicts, political alliances, waves of immigration, nomadism, diasporas, and colonial empires reshaped the borders, drawing new linguistic cartographies, therefore marginalizing those who found themselves isolated from their original territory or community.

7 Q'aras : aymara word for Whites ; Mis'is = person of mixed-race.

3-1 Main legal frameworks on minority rights.

Being aware of the emergency to protect minorities, on behalf of peace and democracy, international and supranational organizations started producing a succession of treaties, covenants, charters, directives and conventions. We now briefly recapitulate some of those founding texts advocating measures to get minorities out of exclusion and promote what can make them "visible" in the public sphere.

After the two warlike tragedies that destroyed Europe and had a devastating to extend the rights for minorities to the field of education or the use of the language.

impact
At world-wide scale, the UNO also offers a legal framework intended to protect minorities, assimilating, among other things, the practice of one's mother tongue to political and civil rights. Article 27 of the Universal Covenant signed in 1966 says: In those States in which ethnic, religious or linguistic minorities exist, persons belonging to such minorities shall not be denied the right, in community with other members of their group, to enjoy their own culture, to profess and practise their religion, or to use their own language.

In the same spirit, UNESCO worked for the rights of minorities, particularly with the Convention against discrimination in education, adopted in 1960 and recommending to recognize the rights of members of national minorities to carry on their own educational activities, including the maintenance of schools and, depending on the educational policy of each state the use of teaching of their own language. 9 Moreover, the international organization contributes significantly to investigating the endangered 8 http://www.echr.coe.int/NR/rdonlyres/D5CC24A7-DC13-4318-B457-5C9014916D7A/0/CONVENTION_ENG_WEB.pdf 9 In article 5 (c) of the Convention which, however, carefully brings reserves allowing the States to assess the standards of education and to ensure intercultural dialogue and bilingualism. http://www.unesco.org/education/pdf/DISCRI_E.PDF languages of the world with the publication of a regularly-updated atlas. [Wurm, 2001;Moseley, 2010] On the south American continent, a number of countries belonging to the American Convention on Human Rights got together on November 1969 to sign the Pact of San José de la Costa. One important chapter is related to the equality of rights: the struggle against all forms of discrimination, prohibition of slavery, freedom of conscience and religion, freedom of expression However, even though some of the measures directly concern the first native inhabitants, there is no explicit reference language minorities as such. Indeed, it is not until 1989 that the International Labour Organization (ILO) produces the Indigenous and Tribal Peoples Convention -C169 10 whose article 28 mentions linguistic rights: 1-Children belonging to the peoples concerned shall, wherever practicable, be taught to read and write in their own indigenous language or in the language most commonly used by the group to which they belong. When this is not practicable, the competent authorities shall undertake consultations with these peoples with a view to the adoption of measures to achieve this objective. 2. Adequate measures shall be taken to ensure that these peoples have the opportunity to attain fluency in the national language or in one of the official languages of the country. Two European conventions take into account the minorities of its member starts. The European Charter for regional or minority languages, 11 adopted in 1992 and applied in 1998, proposes a series of measures designed to protect and promote languages of minorities in the fields of education (Art. 8), judicial authorities (Art. 9), administrative authorities and public services (Art. 10), media (Art. 11), Cultural activities and facilities (Art. 12), Economic and social life (Art. 13) and Transfrontier exchanges (Art. 14 3-2 Main issues at stake.

To sum up the main advances offered by international or supranational organizations, 5 elements may be pointed out:

1.

All measures intend to fight against discrimination, racism, exclusion from the public sphere; recognizing minorities is considered as a sign of democracy and social peace.

2.

On the whole, practicing one's mother tongue is based on the principle that linguistic rights are part of the human rights and fundamental freedoms.

3.

In all cases, there is an attempt to define the notion of "minority", at least "National minorities" with the obvious risk of forgetting the languages spoken by immigrants or diasporas. The European Council is the only organization offering, through the Charter for regional or minority languages, a real project aimed at revitalizing minority tongues in everyday-life activities.

5.

In the case of ILO directives, the rights that are put forward expressly intend to fight against the exploitation and despoilment natives were the victims of.

In short, since the Second-world war, the future of minorities is a real concern for most democratic countries. However, the international conventions and treaties do not have force of law; the States can use the recommendations to conduct their language policies or stick to a minimum in term of minority rights.

4-Planning language diversity : the weight of national realities.

Of course, all the conventions and treaties have been signed and often ratified by the official representatives of the member states; this should guarantee a quick implementation of language planning policies by the concerned countries. As a matter of fact, this is far from being the case.

12 http://conventions.coe.int/Treaty/en/Treaties/html/157.htm

4-1 The socio-political context.

The first obstacle is the reluctance to grant minoritized languages an official status. The constitutional texts in force in most countries give an interesting perspective on the situation minority languages have to face.

As seen before, most countries elected one unique official language when they emerged as Nation-States or developed as Empires. Such choice was seen as a condition to guarantee political unity and communication between the central power and its periphery. In the field of education and media, this centralized tradition long shaped the relationships between government policies and minority languages.

Historically speaking, language planning is the result of each country's cultural and political heritage. In this respect, the French case is representative in terms of the fate of regional languages during the Revolution. French became the official language of the new nation on behalf of Universal Reason and Enlightenment. As More recently, in another context, Peru officially instituted bilingual and intercultural education (Art. 17 of the 1993 Constitution) 13 . The project was carried on by the Ministry of education 14 and led to so paradoxical results that one might say that the spirit of the law has been corrupted. As commented by Jacques Leclerc: French. [Leclerc, 2011] In other words, the bilingual programme keeps on acculturating the natives to the Spanish language and culture while it is profitable to the upper-class children who are linguistically prepared to the enter a globalized economic market and get the best jobs.

Intercultural
In many ways, language is a new socio-political issue. In fact, multilingualism became a chapter of the European policies only in the 1990s 15 . As for the devolution or decentralization processes launched in countries like Great Britain and Spain, they undoubtedly were the example to follow and minorities claims appeared to be more legitimate than ever: why would it be impossible to do what some other countries managed to set up without threatening their institutional organization.

But, the weight of national realities is still strong and when dealing with the situations minority languages have to face, three typical models may be found:

1. One official language is mentioned in the Constitution: France since No reference whatsoever to an official language, either because the issue is an explicit one like in Argentina and Chile where Spanish is the de facto the language of the country [Leclerc, 2011] or in the US for the same reason, or because the other languages have no legal status (The Baltics are quite reluctant towards Russian speakers).

Let us say that the socio-political situation has a major impact on the presence of minority languages in the media, especially on radio and television.

4-2 The audio-visual models.

When (1946) andFinland (1947), in Welsh on BBC (1950s), in Frisian on Omrop Fryslân (1950s) [Moragas, Garitaonandía & López, 1999], or in Breton in 1959. Following radio a few years later, television opened "windows" to minority languages : Irish in Ireland (1960), Welsh in the United Kingdom (1964), Breton (1964) and Basque (1971) in France, Frisian in the Netherlands (1979)18 . [Guyot, 2007] Even if important changes occurred in the 1980s, especially with the deregulation of audiovisual systems, the arrival of private channels or the digitalization of broadcasting, the PSB model is still strong in Europe and guarantees a minimum of visibility for minorities, at least on television 19 .

Outside Europe, audiovisual media are usually a matter of private business. In South America, most counties inherited the American model where financing the production industry and the broadcasting logistics is entrusted to commercial investors. Indeed, private-owned media are hegemonic and many prosperous television companies are based in countries like Brazil or Mexico. After decades of dictatorship and censorship, there is no real public-service tradition and television owners are more concerned with selling air time to advertisers than offering slots to minority programmes. No need to say that minority culture and languages are invisible on television. The production of contents is left to the initiative of associations and independent institutions that have to negotiate with private channels to get air time. This is the case in Peru where the Association Tarpurisunchis, founded in 2003, developed an integrated environmental and educational project in the region of Apúrimac combining a school for Quechua children with a television programme called Saqrakuna. 20 The first series of six 26-minute episodes, produced in includes short subjects on music, craft, history, natural or historic sites that are commented in Quechua and subtitled in Spanish. Saqrakuna was awarded several prizes in festivals and extended its activities to the production of radio programmes in Quechua. The main obstacle the association has to face is to convince television owners to grant free slots on private channels whose sponsors are local enterprises and big advertisers targeting Spanish-speaking audiencesincluding in region like Apúrimac where there is a majority of Quechua speakers.

5-Minority language media

: the issues at stake.

The previous example shows that the increase of television channels thanks to digital networks mostly benefited privates companies, making it almost impossible for minorities to promote their culture and language in the media. The Peruvian case is not an exception.

5-1 Restricted access to media and broadcasting.

Access to audiovisual media is linked to the general situation of minorities at the national level and therefore is a socio political problem. On the whole, few countries actually recognize their language minorities. Some sign conventions they never ratify: of the 47 member-states belonging to the European Council, 33 signed the European Charter for regional or minority languages and 25 ratified it, slowing down the application of concrete measures to protect endangered tongues. Although many European countries still have PSB systems, minorities feel the access they have to specific slots is far too limited.

On PSB televisions, minority languages only get a few hours every week with no real hope of development. The low volume of programmes cannot efficiently contribute to revitalize language practice. Two reasons account for this situation.

First of all, when dealing with minority languages, national statutes applying to public service media are limited: in the list of obligations assigned to public media, linguistic issues are one of the many obligations and no quotas are fixed. This means in order to ensure political and social cohesion, priority is given to content with a common cultural background, thus leaving aside language diversity. Secondly, it is always difficult to promote a "regional" language within a national media system. If most countries have a regional network, few give their regional or local channels real autonomy. This is why many minority-language production units suffer from endemic lack of funding or, at least, from drastic dependence on subsidies and public institutions (Guyot, Ledo & Michon, 2000: 73).

Two other factors need to be underlined as they clearly play against full access to audiovisual media, in particular to television channels: the development of cultural industries and the increase of media concentration. As a matter of fact, within the last 20 years, in a context of internationalization of media and information flows, the production and circulation of cultural goods have been widely monopolized by a small number of big international companies. [UNESCO Report, 2009] Now, the market for audiovisual programmes is a globalized one; this means that language diversity is usually considered as a main economic obstacle to the circulation of content that needs to be dubbed or subtitled. In other words, minority language programmes are viewed by cultural industries as a niche market, i. e. a less lucrative activity with high-cost productions and small audiences.

5-2

The role of associations in audiovisual production and broadcasting.

The only alternative left for minorities is to take their destiny in hand, in order to make up for the political shortcomings. As seen before, producing television programmes remains quite feasible for a group of determined and creative people having light digital video equipment and modest means resulting from sponsoring with public institutions like ministries, or NGO. The series Saqrakuna, produced by

Tarpurisunchis, is composed of 10 highly-motivated youngsters: two producers holding concurrently the jobs of director/cameraman for the first one and presenter for the second, the others presenting the subjects. Post-production is made at the Catholic University of Lima (PUCP). 21 Of course, the main problem for the association is to get free slots to broadcast the series on regional and national television channels, but the producers of Saqrakuna also explored other solutions:

public screenings are organized in the villages of the Apúrimac, DVDs are distributed within the association's network, episodes are available on YouTube, the team participates in film festivals to promote their project. In the end, the work done begins to bear fruit and is being recognized. Tarpurisunchis project is a new approach to socio-political issues in a region where the guerrilla movement El Sentero luminoso was dominant until recently. The association is ideologically on the left, but has a different strategy based on the idea that social advances can be obtained thanks to small-scale experiences, integrating the local population and developed at a local or regional level; the initiatives intend to set an example of what could be done in terms of public policies. Far from the radical change advocated by the guerrilla movement, the Tarpurisunchis association is in line with the work of the philosopher John Holloway whose book Change the world without taking the power is inspiring many political activists in Latin America. [Holloway, 2002] However, television projects are usually harder to handle, contrary to radio.

Indeed, the situation is quite different. Thanks to low-operating and production costs, cheap transmitters and receivers, a broadcasting range perfectly fitted to the local and regional dimension, light mobile equipment, the independent radios launched by minorities constitute the most equally-distributed and developed media in Europe [Guyot, 2007] but also in the rest of the world.

In Europe, there are radio stations in all countries; they are usually bilingual, alternating programmes in the minority language and in the official dominant tongue. This strategy is interesting as it is a good way to attract newcomers, whether they know the language or nor. In Latin America, radios are also widespread and are often called "community radios" as they also fulfil social purposes: advice on health,

21 Interview with the two producers in June 2010 and screening of the series.

agricultural techniques, rural development, food safety, gender equity, etc 22 The linguistic issues are present but not necessarily a priority. Here again, in a context of domination of native inhabitants, the main issue at stake is to help people to get out of poverty and to promote education and social equality.

A few clues to conclude.

Undoubtedly, the awareness that protecting language minorities is a central issue is not just a passing fad. For the last twenty years, international institutions have clearly been legislating in that sense. However, applying international recommendations depends on the level of mobilization of minorities. Indeed, the measures taken by governments are directly related to the initiatives, experiences and struggles organized by minority groups, associations, collectives of activists or NGOs. It is a matter of relations of power.

Of course, one can argue that the existence of rights designed to protect minorities, as well as freedom of expression, as defined in most international texts and national constitutions should now be enough to guarantee full access to media.

But, as we pointed out, national socio-political backgrounds, media concentration plus the worldwide development of cultural industries show that freedom of expression can be an illusory right. This is why another type of legal principle is more and more referred to as a necessity by those who fight for the democratization of audiovisual media: communication rights. Indeed, what is the sense of having the freedom of expression when it is impossible to share the means or channels of communication?

To take the example of Digital Terrestrial Television in Europe, most channels were allocated to private multimedia companies to the detriment of small or local community groups. In June 2011, the European Audiovisual Observatory surveyed 19 E.U. countries. The results are conclusive: free DTT accounts for 47% of the almost 1800 channels available. Free DTT channels are shared between the private (60%) and the public (40%), but 92% is private when dealing with Pay DTT platforms. There are 54% of local and regional channels, 37% of national and 9% of international television. 23 Let us underline that when the survey talks about local or regional channels, these are in fact private-owned media whose financing comes mainly from advertising. In short, if three criteria are mixedpublic, free and local -, almost no place is reserved to minority groups.

In the field of radio, the World Association of Community and Radio Broadcasters (AMARC), an NGO founded in 1983 gathering 130 countries, is trying to democratize the access to radio and to limit the monopoly of private companies over wavebands. • Giordan Henri (dir.) (1992), Les minorités en Europe. Droits linguistiques et droits de l'homme, Paris : Kimé.

• Guyot Jacques (2007), "Minority language media and the public sphere", in Minority Language Media: Concepts, Critiques and Case Studies, Dr Mike Cormack and Niamh Hourigan eds., Clevedon, Buffalo, Toronto : Multilingual Matters Ltd, pp.

34-51.

• Guyot Jacques (2006), "Les médias pour les minorités comme objet de recherche", in Cahiers franco-canadiens de l'Ouest, vol. 18, n° 2, pp. 119-141.

• Guyot Jacques ( 2004), "Languages of minorities and the media. Research issues", in

Mercator Media Forum n°7, Caerdydd: Gwasg Prifysgol Cymru, pp. 13-28.

• Guyot Jacques, Ledo Margarita & Michon Rolland (2000), "Production télévisée et identité culturelle en Bretagne, Galice et Pays de Galles -Produerezh skinwel hag identelezh sevenadurel e Breizh, Galiza ha Kembre", Klask, n° 6, Rennes: Presses universitaires de Rennes, 190 p.

• Hagège Claude (2000), Halte à la mort des langues, Paris : Odile Jacob.

  3. Measures shall be taken to preserve and promote the development and practice of the indigenous languages of the peoples concerned. Let us note that the scope of the recommendation is considerably reduced by the expression "wherever practicable". Besides, article 14 of the Convention emphasizes the rights over traditional lands and article 15 holds that natives can fully participate to the use, management and conservation of the natural resources.

  analyzed by three anthropologists, this was made possible thanks to the equivocal attitude of the Revolutionaries towards the idioms and dialects spoken in the French countryside, viewed as a "rural matrix" populated by a humanity remained on the edge of history and whose life would be governed by nature [which is] at the same time the original garden and the dark reserve of animality.[De Certeau and al., 2002 : 151] The Barère Report, produced in January 1794 by the Committee of public security to assess the different tongues spoken in France, clearly illustrates this bias in the middle of the age of enlightenment when the author associates regional tongues to clericalism, irrationality, cultural backwardness and counter-revolutionary ideas : The idiom called lower-Breton, the Basque idiom, the German and Italian languages perpetuated the rule of fanaticism and superstition, secured the domination of priests, nobility and men of law, stop the Revolution from getting into nine important "departments" and may favour the enemies of France.[De Certeau, 2002 : 123] Nowadays, the same stigmas are applied to minorities, with an extension to the immigrantsespecially when they come from former coloniesand nomads.Reluctance to plan the coexistence of different languages may come from a more recent but traumatic history. This is what happened when former communist countries gained their independence after 1989: Russian was usually banned and each country went back to its original vernacular idiom, viewed as the cement of the new national identity and political unity, just like the Nation/States that emerged in the 18 th century.

  But, until now, only one country has taken the plunge in terms of communication rights: Argentina. In 2009, the law for audiovisual services of Argentina (LSCA 26.522) was enacted. According to the spirit of the communication rights go beyond the principle of freedom of expression because they alone can guarantee democratic access to all citizens. The law states that 33% of TV and radio frequencies are reserved to non-profit organizations: cooperatives, universities, indigenous people, communities and the State. In an international context of media concentration, this text is an essential part to prevent the means of communication from falling under the control of commercial interests. As for minorities, the law can have a positive impact on the defense and promotion of their cultural and linguistic idiosyncrasies. It is, at least, a useful and essential element to complete the other legal measures and rights. Following the Argentinian example, Bolivia should soon introduce communication rights into law. Let us hope than other countries will be inspired by this courageous decision to rehabilitate the idea that communication means are a common good. Bibliography : • Anderson Benedict (2002), L'imaginaire national. Réflexions sur l'origine et l'essor du nationalisme, Paris : La Découverte. (Imagined communities. Reflections on the origin and spread of nationalism, London : Verso, 2006) • Barré Ronan (2007), Les langues celtiques, entre survivance populaire et renouveau élitiste, Rennes : Presses universitaires de Rennes. • Benda Julien (1933), Discours à la nation européenne, Paris: Gallimard. • Benda Julien, Conference (1947), Septembre 2nd 1946, in J. Benda, G. Bernanos, K. Jaspers and al. L'esprit européen: conférences et entretiens des Rencontres internationales de Genève, 1946, Paris: Oreste Zeluck. • Bourdieu Pierre (1982), Ce que parler veut dire. L'économie des échanges linguistiques, Paris : Fayard. (Language and Symbolic Power, Harvard University Press, 1991) • Calvet Louis-Jean (2002), Le marché aux langues. Les effets linguistiques de la mondialisation, Paris : Plon. • Crystal David (2000), Language Death, Cambridge : Cambridge University Press. • De Certeau Michel, Julia Dominique & Revel Jacques (2002), Pour une politique de la langue, Paris : Gallimard (coll. Folio histoire). • García Linera Àlvaro (2008), Pour une politique de l'égalité. Communauté et autonomie dans la Bolivie contemporaine, Paris : Les Prairies ordinaires.

  for the rest of the world in the first half of the 20 th century, the Council of Europe considered it essential to guarantee national minorities' rights within a

mosaic of peoples speaking some 200 languages, in order to preserve peaceful coexistence. The Council is quite explicit about the prohibition of any form of discrimination in Article 14 of the European Convention on Human Rights voted in November 4 th 1950: The enjoyment of the rights and freedoms set forth in this Convention shall be secured without discrimination on any ground such as sex, race, color, language, religion, political or other opinion, national or social origin, association with a national minority, property, birth or any status. 8 Additional protocols amended the text in order

  ). Each ratifying party undertakes to apply a minimum of 35 paragraphs or sub-paragraphs of the Charter, with at least 3 chosen in articles 8 and 12, and one from articles 9, 10, 11 or 13. As for the Framework Convention for the Protection of National Minorities signed in 1995 and ratified in February 1998, it offers a general contract supposed to protect national minorities like the Romanis, but also the Hungarians living in Romania, or the German community in Poland.12

10 http://www.ilo.org/dyn/normlex/en/f?p=1000:12100:0::NO::P12100_INSTRUMENT_ID:312314 11 http://conventions.coe.int/treaty/en/Treaties/Html/148.htm

  bilingual education is not designed to preserve native tongues, but to teach children so they can quickly read and write Spanish. It is a bilingualism of transition, not a bilingualism of preservation. Moreover, parents have no choice, except for private schools (for the rich) where bilingualism concerns Spanish and English, or Spanish and French, etc. In reality, the true intercultural bilingualism is only worth for rich children attending private or international schools that offer bilingual classes in Spanish and in English, sometimes in

Pierre Bourdieu had a major impact on the left-wing intellectuals in South America, for example the sociologist and Bolivian Prime Minister Álvaro García Linera.

At that time, European linguistic diversity was considered as a main obstacle to political unity and many people, like the writer Julien Benda, wanted to promote French as a supranational language in the E. U.[Benda, 1933 ; 1947]

The expression internally colonized is a much-discussed term, as it would supposedly be perilous to compare the situation of peoples integrated to the Nation-States to the fate met by those who were subdued, often violently, by forces coming from other continents.[Barré, 2007 : 136-138] However, on thinking it over, if we agree on defining colonization as a relation of domination, including what has to do with the division and exploitation of labour, the term is quite relevant, particularly when opposed to the externally colonized.

Bolivian civil servants have to know a second native tongue in addition to Castilian, considered as the administrative language.

This classification belongs to Jacques Leclerc, a specialist of language policies. See bibliography.

During Franco's dictatorship, minority languages were not present in audiovisual media. The situation changed when Spain became a democracy and voted a new constitution in

1978, leading to a policy of decentralization. As for Italy, things changed more recently with a regional law voted in 1996, followed by two others in 2007 and 2010; they aim at encouraging the protection and promotion of Italian minority languages : Friulan, German, Sardinian, Slovenian 19 Television is an expensive media for small groups. But, it also confers a strong legitimacy on any linguistic cause.[Guyot, 2007]

http://www.tarpurisunchis.org.pe/; interviews with the director Javier Malpartida and two producers of Saqrakuna, Dennis Quispe Salas and Hernán Ramírez Condori in June 2010. To view the programme, go to http://www.isuma.tv/hi/fr/members/tarpurisunchis

Interview with Leonidas Casas Ballón, former director of the radio programme Tierra Fecunda, Lima, June 2010.

http://www.obs.coe.int/about/oea/pr/mavise_juin2011.html?print

• Holloway John (2005), Change the world without taking power. The meaning of revolution today, New York : Pluto Press, (2 nd edition).

• Keucheyan Razmig (2010), Hémisphère gauche. Une cartographie des nouvelles pensées critiques, Paris : La Découverte (coll. Zones).

• Kymlicka Will (1995), Multinational citizenship: a liberal theory of minority rights, Oxford: Oxford University Press.

• Leclerc Jacques ( 2011 Unesco (Online version http://www.unesco.org/culture/en/endangeredlanguages/atlas)


Hideaki Uchiyama
email: hideaki.uchiyama@inria.fr

Eric Marchand
email: eric.marchand@irisa.fr

Object Detection and Pose Tracking for Augmented Reality: Recent Approaches

Keywords: Augmented Reality (AR), Detection, Tracking, Pose Estimation, Survey

This paper introduces recent progress on techniques of object detection and pose tracking with a monocular camera for augmented reality applications. To visually merge a virtual object onto a real scene with geometrical consistency, a camera pose with respect to the scene needs to be computed. For this issue, many approaches have been proposed in the literature. In this paper, we classify and summarize the recent trends of the solutions as a survey.

Introduction

Augmented reality (AR) is an increasingly-recognized paradigm of information visualization that merge a computer-generated virtual object onto a real scene to visually augment reality [START_REF]Handbook of Augmented Reality[END_REF] . Azuma has summarized three requirements in AR applications as follows [START_REF] Azuma | A survey of augmented reality[END_REF] :

( 1 ) combines real and virtual, ( 2 ) interactive in real time, ( 3 ) registered in 3-D.

To achieve these requirements, numerous technologies on computer vision and image processing have made immense contributions. With a monocular camera, 3D structure of a real scene is sensed to enable overlaying virtual objects with geometrical consistency in real-time. Virtual objects are typically visualized with one of three devices: a head-mounted display (HMD), a handheld display [START_REF] Wanger | Handheld Augmented Reality[END_REF] or a projector [START_REF] Bimber | Spatial Augmented Reality: Merging Real and Virtual Worlds[END_REF] .

Recently, the algorithms of object detection and pose tracking have been incorporated in AR applications. In such systems, a number of objects are first registered on a database. When one of the registered objects is captured, it is recognized, tracked and localized to overlay its corresponding virtual object on it. For target objects, various types of size and shape can be used such as a small planar paper, a large room and so on. In the literature, many approaches of localization have been proposed.

In this paper, we classify and summarize recent techniques on monocular camera based object detection and pose tracking for AR applications as a survey. So far, some survey papers on AR have been published. Teichrieb, et al. focused on visual tracking based on model based tracking and structure from motion [START_REF] Teichrieb | A survey of online monocular markerless augmented reality[END_REF] . Ong, et al. introduced research issues for developing applications in manufacturing [START_REF] Ong | Augmented reality tions in manufacturing: a survey[END_REF] . Krevelen and Poelman sum-marized general research issues on AR such as display, camera tracking and user interaction [START_REF] Van Krevelen | A survey of augmented reality technologies, applications and limitations[END_REF] . Our objective is similar with a survey of object tracking by Lepetit and Fua [START_REF] Lepetit | Monocular model-based 3D tracking of rigid objects: A survey[END_REF] and Yilmaz, et al. [START_REF] Yilmaz | Object tracking: A survey[END_REF] .

Definition

We first define detection and tracking with a monocular camera in the context of AR. Also, we summarize the meaning of some terminology frequently used in the literature.

Detection

Detection has several meanings depending on research issues. In the context of AR, detection is a process that localizes a target object in a captured image and computes a camera pose with respect to this object.

Detection is sometimes reworded with several terms. initialization is used because detection is an initial process for tracking [START_REF] Kotake | A fast initialization method for edge-based registration using an inclination constraint[END_REF] . Detection is also considered as registration that finds best transformation parameters for fitting two different models because pose estimation involves alignment between a captured image and a reference object [START_REF] Rekimoto | Matrix: a realtime object identification and registration method for augmented reality[END_REF] . Both initialization and registration are usually used when the number of target objects is only one.

If multiple target objects are registered on a database, object identification is included in object detection such that a target object is identified and localized in a captured image [START_REF] Rekimoto | Matrix: a realtime object identification and registration method for augmented reality[END_REF] . This process is also called recognition [START_REF] Takacs | Unified real-time tracking and recognition with rotation-invariant fast features[END_REF] or retrieval [START_REF] Pilet | Virtually augmenting hundreds of real pictures: An approach based on learning, retrieval, and tracking[END_REF] .

Tracking

In contrast to detection that estimate a camera pose for one image, tracking is camera pose estimation in temporal image sequence. For seamless augmentation of target objects, tracking is an important issue.

Tracking is reworded according to the configuration of a camera and an object. If a camera is fixed and captures a moving object in a scene, this is called outside-in tracking because the object is observed from outside. If a camera is movable such as a handheld device and capture a fixed/moving object, this is called inside-out tracking.

A technical issue on both cases is common such that a relative camera pose with respect to a target object is computed.

The technical framework of tracking is divided into two types as follows.

Tracking by Detection

Computing a camera pose with detection in every frame is named tracking by detection or tracking by matching. In other words, a camera pose is always computed by matching between an input image and a reference with a detection technique. No previous camera pose is used for the estimation of current camera pose. Pose tracking with randomized trees [START_REF] Lepetit | Keypoint recognition using randomized trees[END_REF] or ferns [START_REF] Ozuysal | Fast keypoint recognition using random ferns[END_REF] are examples of such approaches.

Tracking by Tracking

Computing a camera pose using its previous pose is named tracking by tracking, frame-by-frame tracking, frame-to-frame tracking or recursive tracking. Most of these approaches are based on the minimization of camera displacement between two successive images. In the optimization, previous camera pose is used as an initial camera pose. In Section 5, we introduce the details of these approaches.

Pose Estimation

Before starting the detailed explanation of object detection and pose tracking, we introduce the overview of projection models and pose estimation [START_REF] Hartley | Multiple View Geometry in Computer Vision[END_REF] . A projection model is basically selected depending on the shape of a target object. The solution of pose estimation has been proposed in the literature known as direct linear transformation (DLT) or perspective-n-point (PnP) problem.

Planar Object

The geometrical relationship between a reference planar object and an input image is described with a homography. Homography is a member of SL(3) (special liner group). With 2D-2D point correspondences, a homography matrix H that satisfies the following expression is computed:

min H i x r i -P Hx t i • • • • • • • • • • • • • • • • • • • • • (1)
where x r i is an image coordinate of a point on a 2D reference, x t i is that of its corresponding point on a target,˜means a homogeneous coordinate and P (•) returns an image coordinate computed from the dehomogenisation of an input homogeneous coordinate. Basically, this expression represents the minimization of reprojection error in an image. Note that rotation and translation components of a camera can be extracted from a homography for augmentation in 3D [START_REF] Hartley | Multiple View Geometry in Computer Vision[END_REF] .

Non-Planar Object

For a camera pose with respect to a non-planar object, following 6 degreeof-freedom (DoF) transformation matrix M is used;

M = R t 0 1 • • • • • • • • • • • • • • • • • • • • • • • • • • • • (2)
where R ∈ SO(3) (special orthogonal group) and t ∈ R 3 . Therefore, M is a member of SE(3) (special Euclidean group). With 2D-3D point correspondences, M that satisfies following expression is computed:

min M i x i -P A (I|0) M Xi • • • • • • • • • • • • (3)
where X i is a 3D coordinate of a point on a 3D reference, x i is an image coordinate of its corresponding point on an image and A is a camera calibration matrix.

SLAM

Simultaneous localization and mapping (SLAM) enable wide-area tracking in unknown environment [START_REF] Davison | Real-time localisation and mapping with wearable active vision[END_REF] . Especially, Klein and Murray proposed parallel tracking and mapping (PTAM) as a novel SLAM framework specialized for AR applications [START_REF] Klein | Parallel tracking and mapping for small AR workspaces[END_REF] . In PTAM, the processes of tracking a camera pose and updating new maps are performed in different threads on CPU such that a camera pose is tracked in all incoming images on one thread while new map is updated with batch processing on the other thread only when needed.

In SLAM, both 3D map X i and camera motion M j that satisfy following expression are computed: min Xi,Mj i,j

x ij -P A (I|0) M j Xi • • • • • • • • (4)
where x ij is a tracked keypoint of i-th keypoint in j-th image.

The key technology in SLAM is structure from motion (SfM), bundle adjustment and extended kalman filter (EKF) [START_REF] Hartley | Multiple View Geometry in Computer Vision[END_REF] . With SfM, camera motion between two images is estimated by computing a fundamental matrix with keypoint correspondences, and then 3D map is estimated by triangulating the correspondences. Estimated camera motion and 3D map are finally optimized using bundle adjustment described in Equation 4. EKF is used for pose estimation with temporal data.

Robust Estimator

In established keypoint correspondences between two objects, outliers may be included because of noise or other factors and degrade the accuracy of pose estimation. In practice, it is necessary to estimate a precise camera pose even in the presence of outliers. As a solution, a robust estimator is incorporated into pose estimation [START_REF] Stewart | Robust parameter estimation in computer vision[END_REF] .

The simplest method is to minimize the least-meansquare (LMS) of the reprojection error for all correspondences. However, all correspondences including outliers are equally dealt and outliers cannot be removed with this method. Thus, outliers with huge error degrade the accuracy. M-estimator is considered as an alternative to LMS. In M-estimator, a weighting function according to error magnitude is incorporated to reduce the influence of outliers with huge error. Random sample consensus (RANSAC) is a method that iteratively and randomly samples some keypoints and compute a camera pose with LMS [START_REF] Fischler | Random sample consensus: a paradigm for model fitting with applications to image analysis and automated cartography[END_REF] . Random sampling is iteratively performed to find a camera pose that includes least outliers. PROSAC is considered as RANSAC with an efficient sampling strategy. In PROSAC, keypoints are sampled from most reliable correspondence such as a correspondence with minimum distance of descriptors [START_REF] Chum | Matching with PROSAC -progressive sample consensus[END_REF] . Leastmedian-of-squares (LMedS) algorithm is to find a camera pose with the smallest value of the median of squared residuals for all correspondences.

Detection

In this section, we classify the detection approaches as follows: fiducial markers, natural keypoints and natural edges. Especially, we focus on the techniques of recognition and retrieval that can deal with multiple rigid objects.

4.1 Fiducial Marker 2D fiducial markers have been used as a reference object for a long time. Compared with natural feature based approaches, fiducial markers can stably be extracted because its color and shape are defined beforehand.

The world's first square marker system was developed by Rekimoto in 1998 [START_REF] Rekimoto | Matrix: a realtime object identification and registration method for augmented reality[END_REF] . The marker has a black bold frame for camera pose estimation. Inside the frame, there is a coded square black and white pattern for marker identification. This type of ID-embedded markers has been developed with different shapes and identification techniques [START_REF] Fiala | ARTag, a fiducial marker system using digital techniques[END_REF] (51) (80) (84) [START_REF] Wagner | ARToolKitPlus for pose tracking on mobile devices[END_REF] .

ARToolKit is another type of marker system that needs the database of patterns included inside the frame [START_REF] Kato | Marker tracking and HMD calibration for a video-based augmented reality conferencing system[END_REF] . As well as other square markers described above, the marker has a black bold frame. Any texture pattern can be inserted inside the frame and identified with simple template matching.

Even at the present, new types of fiducial markers are still being developed to relax the constraint of the marker shape and improve the recognition stability and scalability. Uchiyama and Saito developed random dot markers that use randomly scattered dots as fiducial [START_REF] Uchiyama | Random dot markers[END_REF] . The detection of the marker is based on keypoint matching with geometrical features described by LLAH [START_REF] Nakai | Use of affine invariants in locally likely arrangement hashing for camera-based document image retrieval[END_REF] . Compared with square markers, the shape of a random dot marker is flexible and the robustness against occlusion is high. RUNE-Tag also uses dots as fiducial such that dots are distributed on a circle with a certain pattern coding [START_REF] Bergamasco | RUNE-Tag: A high accuracy fiducial marker with strong occlusion resilience[END_REF] . This work evaluated the accuracy of pose estimation with four corners in ARToolKit and that with the centers of dots in RUNE-Tag. In the presence of noise and blur, camera pose computed from RUNE-Tag is more accurate than that of ARToolKit because RUNE-Tag can use more points for pose estimation.

Keypoint

Natural keypoint based approaches have been well-investigated for a long time. The basic framework of these approaches is divided into extraction, description and matching.

Extraction

Extraction consists in finding pixels which have different appearance from other pixels. Extraction is also reworded as detection such as keypoint detection [START_REF] Tuytelaars | Local invariant feature detectors: A survey[END_REF] .

Harris corner detector is the most famous detector that is compared with other detectors as a benchmark [START_REF] Harris | A combined corner and edge detector[END_REF] . FAST corner detector select a pixel that has higher or lower value than neighbors with a machine learning technique [START_REF] Rosten | Faster and better: A machine learning approach to corner detection[END_REF] . Mair, et al. improved FAST by building an optimal decision tree [START_REF] Mair | Adaptive and generic corner detection based on the accelerated segment test[END_REF] . In some approaches, a local extrema of scale space is extracted as a keypoint. Scale space is built with differences of Gaussian (DoG) in SIFT [START_REF] Lowe | Distinctive image features from scale-invariant FCV2012 keypoints[END_REF] , approximated Laplacian filters in CenSurE [START_REF] Agrawal | CenSurE: center surround extremas for realtime feature detection and matching[END_REF] and fast Hessian in SURF [START_REF] Bay | Speeded-up robust features (SURF)[END_REF] .

Description

A vector that describes the feature of a keypoint is computed for the comparison between two keypoints. The approaches of local texture based description are widely investigated and divided into two types: histogram of gradient and binary test.

Histogram of gradient is computed from quantizing gradients within a local region and putting into bins. In SIFT [START_REF] Lowe | Distinctive image features from scale-invariant FCV2012 keypoints[END_REF] , a local region is divided into sub-regions and histogram of gradient is computed in each sub-region. This approach is used in several methods (2) (8) [START_REF] Wagner | Pose tracking from natural features on mobile phones[END_REF] that improved sampling strategy of gradient and computational efficiency.

A binary test is a simple comparison of the intensity of two pixels and produces a binary result that represents which pixel is brighter. Hundreds of binary tests are performed to compute a feature vector because a binary test is not enough discriminative. The main research issue of this approach is the efficient sampling of two pixels (12) (42) (56) [START_REF] Rublee | ORB: an efficient alternative to SIFT or SURF[END_REF] .

Instead of using local texture, local geometry of keypoints is used to compute a feature vector [START_REF] Uchiyama | Toward augmenting everything: Detecting and tracking geometrical features on planar objects[END_REF] . In this approach, neighbor keypoints are first extracted and geometrical invariant is computed from neighbor keypoints [START_REF] Nakai | Use of affine invariants in locally likely arrangement hashing for camera-based document image retrieval[END_REF] . Because this approach does not use local texture, this is applicable to keypoint matching for both rich and weak texture.

Matching

To match keypoints between an input and a reference, feature vectors of keypoints in the reference are stored in a feature database. For each keypoint in the input, the most similar feature vector in the database is searched.

If a feature vector has large dimension such as 128 in SIFT [START_REF] Lowe | Distinctive image features from scale-invariant FCV2012 keypoints[END_REF] , full searching is hardly performed in realtime. Instead, tree based searching is used as approximate nearest neighbor searching (4) [START_REF] Muja | Fast approximate nearest neighbors with automatic algorithm configuration[END_REF] . The searching cost of this approach depends on the number of features stored in the database. Another type of searching is hashing that maps a feature vector to an integer index [START_REF] Datar | Locality-sensitive hashing scheme based on p-stable distributions[END_REF] . This approach is theoretically fast with O(1) regardless of the size of the database, but is sensitive to small error. If a feature vector is described with binary string, full searching with a hamming distance is performed (12) . In keypoint matching with randomized trees [START_REF] Lepetit | Keypoint recognition using randomized trees[END_REF] and random ferns [START_REF] Ozuysal | Fast keypoint recognition using random ferns[END_REF] , matching is treated as a classification problem.

Edge

Compared with keypoint based approaches, edge based approaches are not much investigated. In edge based approaches, a geometrical feature is computed from edges.

Hagbi, et al. proposed a method for recognizing planar shapes and estimating a camera pose from the contour of the shapes [START_REF] Hagbi | Shape recognition and pose estimation for mobile augmented reality[END_REF] . In this method, adaptive thresholding based binarization is first applied to an image to extract shape contours. For each contour concavity, projectiveinvariant keypoints are extracted from bitangent lines, and projective invariant features are computed for recognition. Then, initial camera pose is estimated with those projective-invariant keypoints and refined by minimizing the reprojection error.

Donoser, et al. took a similar approach described FCV2012 above [START_REF] Donoser | Robust planar target tracking and pose estimation from a single concavity[END_REF] . To extract contours, they used MSER (maximally stable extremal regions) that extract blob regions [START_REF] Matas | Robust wide baseline stereo from maximally stable extremal regions[END_REF] . Shape recognition is based on classification of contours that is similar with classification of keypoints [START_REF] Ozuysal | Fast keypoint recognition using random ferns[END_REF] . Synthetic views of each template contour are first trained with random ferns. In run-time, each extracted contour is classified into one of the trained classes and recognized. Pose estimation is based on the extraction of projective-invariant keypoints from bitangent lines.

Tracking

Most of the available tracking techniques can be divided into two main classes: feature-based and modelbased tracking. The former approach focuses on tracking 2D features such as geometrical primitives (point, segments, circles, etc.) or object contours (such as active contours) extracted from images. The latter one explicitly uses a 2D/3D model of the tracked objects. In this section, we introduce the details of these approaches.

Overview

In model-based tracking, the model can be a 3D model leading mainly to a pose estimation process corresponding to a registration process between measures in the image and the forward projection of the 3D model [START_REF] Comport | Real-time markerless tracking for augmented reality: The virtual visual servoing framework[END_REF] [START_REF] Drummond | Real-time visual tracking of complex structures[END_REF] . Within 2D model-based approaches, the object to be tracked can be represented by a descriptor. These descriptors can profile object histogram leading to mean shift like approaches [START_REF] Comaniciu | Mean shift: A robust approach toward feature space analysis[END_REF] or point neighborhood leading to keypoint tracking by matching approaches [START_REF] Lepetit | Keypoint recognition using randomized trees[END_REF] [START_REF] Lowe | Distinctive image features from scale-invariant FCV2012 keypoints[END_REF] . Such approaches are usually very robust to illumination variation, occlusions, etc.

As described in Section 5.2, it is also possible to consider that this 2D model is a reference image (or a template). In that case, the goal is to estimate the motion (or warp) between the current image and a reference template. An example of such approaches are differential tracking methods such as the LK [START_REF] Lucas | An iterative image registration technique with an application to stereo vision[END_REF] or others (6) (9) [START_REF] Hager | Efficient region tracking with parametric models of geometry and illumination[END_REF] . Those approaches are not limited to 2D motion estimation, considering, for example, the motion of a plane in the image space, it is indeed possible to estimate its motion back in the 3D real space.

Template Tracking

A widely considered approach in AR is template tracking. In this context, a measure of the alignment between the reference image and the current image and its derivatives with respect to the motion (warp) parameters is used within a nonlinear estimation process to estimate the current object motion.

Formulation

Differential tracking is a class of approaches based on the optimization of an image registration function f . The goal is to estimate the displacement p of an image template I * in a sequence of images I 0 ..I t . In the case of a similarity function, the problem can be written as:

p t = arg min p (f (I * , w(I t , p))) . • • • • • • • • • • • • • • • (5)
where we search the displacement p t that maximizes the similarity between the template I * and the warped current image I t . For the purpose of clarity, the warping function w is here used in an abuse of notation to define the overall transformation of the image I by the parameters p. Indeed, its correct formulation w(x, p) gives the function that moves a point x from the reference image to its coordinates in the current image.

Basic Alignment Function

One essential choice remains the one of the alignment function f . One natural solution is to choose the function f as the standard sum of squared differences (SSD) of the pixel intensities between the reference image and the transformed current image [START_REF] Baker | Equivalence and efficiency of image alignment algorithms[END_REF] [START_REF] Lucas | An iterative image registration technique with an application to stereo vision[END_REF] :

p t = arg min p (SSD(I * , w(I t , p))) • • • • • • • • • • • • (6) = arg min p x∈ROI (I * (x) -I t (w(x, p))) 2 • • • • (7)
where the summation is computed on each point x of the reference template that is the region of interest (ROI) of the reference image.

Optimization

The displacement p t can be computed with the optimization processes. In the Lucas-Kanade (LK) algorithm, the alignment is based on a Gauss-Newton gradient descent non-linear optimization [START_REF] Baker | Lucas-kanade 20 years on: A unifying framework[END_REF] . A non-linear expression is linearized by using a first order Taylor expansion. In ESM, an efficient second-order minimization was proposed [START_REF] Benhimane | Homography-based 2D visual tracking and servoing[END_REF] . ESM-Blur incorporated a blur model into the optimization of ESM [START_REF] Park | Esm-blur: Handling & rendering blur in 3d tracking and augmentation[END_REF] .

Recent Approaches

Template-based tracking approaches have been extended to region tracking (6) (9) (28) . Such approaches are considered as a standard in planar region tracking and localization for augmented reality application. However, some approaches are not effective in the case of illumination changes and occlusions [START_REF] Baker | Equivalence and efficiency of image alignment algorithms[END_REF] [START_REF] Lucas | An iterative image registration technique with an application to stereo vision[END_REF] . Several solutions have been proposed to add robustness toward those variations.

Some include the use of M-estimators to deal with occlusions or an illumination estimation [START_REF] Hager | Efficient region tracking with parametric models of geometry and illumination[END_REF] [START_REF] Silveira | Real-time visual tracking under arbitrary illumination changes[END_REF] . Others can consider local zero-mean normalized cross correlation (ZNCC) [START_REF] Irani | Robust multi-sensor image alignment[END_REF] , or sum of conditional variance [START_REF] Richa | Visual tracking using the sum of conditional variance[END_REF] to replace SSD. Another solution is to maximize the information shared between the reference image and the sequence by maximizing the Mutual Information (MI) function [START_REF] Shannon | A mathematical theory of communication[END_REF] [START_REF] Viola | Alignment by maximization of mutual information[END_REF] . MI has also proved to be robust to occlusions and illumination variations and can therefore be considered as a good alignment measure for tracking [START_REF] Dowson | Mutual information for lucaskanade tracking (MILK): An inverse compositional formulation[END_REF] [START_REF] Panin | Mutual information-based 3d object tracking[END_REF] . Dame and Marchand proposed to use mutual information for measuring similarity [START_REF] Dame | Accurate real-time tracking using mutual information[END_REF] . This approach can deal with multimodality such that a reference is a 2D geographical map and an input image is its satellite image.

3D Model-Based Tracking

Among the various approaches allowing to get the camera pose, model-based methods have shown growing performances in the past years. The information given by the knowledge of a template or 3D CAD model of the object allows to improve the tracking robustness.

Formulation

When considering complex environment, the pose estimation method as defined in Equation 5has to be reformulated. From a general point of view, the problem is defined as the minimization of the error between contour points extracted from the images and the projection of a 3D model. This approach usually uses the distance between a point and projection of 3D lines [START_REF] Comport | Real-time markerless tracking for augmented reality: The virtual visual servoing framework[END_REF] [START_REF] Drummond | Real-time visual tracking of complex structures[END_REF] [START_REF] Lowe | Fitting parameterized three-dimensional models to images[END_REF] [START_REF] Vacchetti | Combining edge and texture information for real-time accurate 3D camera tracking[END_REF] .

Assuming the camera parameters and an estimate of the pose are known, the CAD model is first projected into the image according to that pose. Formally, the projection of an edge L i of the 3D model according to the pose c M w will be denoted by E i = L i ( c M w ). Each projected edge E i is sampled, giving a set of points {e i,j }. From each sample point e i,j , a search is performed along the edge normal to find strong gradients. In the approach of Comport, et al. [START_REF] Comport | Real-time markerless tracking for augmented reality: The virtual visual servoing framework[END_REF] , the point of maximum likelihood with regard to the initial point e i,j is selected from the exploration step. It is denoted by e ′ i,j in the following. A non linear optimisation approach is then used to estimate the camera pose which minimizes the errors between the selected points and the projected edges [START_REF] Comport | Real-time markerless tracking for augmented reality: The virtual visual servoing framework[END_REF] [START_REF] Drummond | Real-time visual tracking of complex structures[END_REF] [START_REF] Lowe | Fitting parameterized three-dimensional models to images[END_REF] , that is:

c M w = arg min c Mw i,j d ⊥ (E i , e ′ i,j ) • • • • • • • • • • • • • • (8) where d ⊥ (E i , e ′ i,j ) = d ⊥ (L i ( c M w ), e ′ i,j
) is the squared distance between the point e ′ i,j and the projection E i of the linear segment L i of the model.

Optimization

The problem of minimizing this equation has been widely investigated in the past years [START_REF] Lepetit | Monocular model-based 3D tracking of rigid objects: A survey[END_REF] and different approaches have been proposed to address it. Most of these approaches can be divided into two categories:

• Non-linear optimization methods use non linear optimization techniques (Newton minimization, virtual-visual servoing,...) to find the pose which minimizes a given reprojection error between the model and the image edges (15) (22) [START_REF] Lowe | Fitting parameterized three-dimensional models to images[END_REF] . The robustness of these methods has been improved by using robust estimation tools (3) (15) [START_REF] Drummond | Real-time visual tracking of complex structures[END_REF] . However, they can fail in case of large displacements or wrong edge matching, especially in cluttered environment. More constraints that uses texture along with contour information have been proposed [START_REF] Pressigout | Real-time hybrid tracking using edge and texture information[END_REF] . It allows to introduce a spatial-temporal constraints in this problem. • Bayesian methods, on the other hand, have been used to perform the same task by estimating the probability density associated to the pose. This can be achieved by Kalman filtering when the probability density function (p.d.f.) can be represented by an uni-modal Gaussian distribution. More recently, the improvement of computational performances has allowed to consider particle filtering approaches (34) (54) (64) [START_REF] Teulière | 3D modelbased tracking for UAV position control[END_REF] . Instead of going from the low level edges to retrieve the camera pose, particle filtering uses a set of hypothesis on the possible camera poses (the particles). The likelihood of each particle is then measured in the image. Since the space of all possible poses is large, the main issue is to keep a fair representation of the different modes of the state probability distribution while using few particles.

Recent Progress

Another challenge is to consider a complete polygonal 3D model, in order to track complex object. The whole information from the geometrical shape of any kind of scene can be used and a heavy phase of a manual redesign of the model is avoided. Methods that rely on the use of the graphics process units (GPU) and of a 3D rendering engine to manage the projection of the model and to determine the visible and prominent edge from the rendered scene have been proposed [START_REF] Petit | Evaluation of model based tracking with trakmark dataset[END_REF] [START_REF] Reitmayr | Going out: Robust model based tracking for outdoor augmented reality[END_REF] [START_REF] Wuest | Adaptable modelbased tracking using analysis-by-synthesis techniques[END_REF] . An advantage of this technique is to implicitly handle auto occlusions.

AR Framework

To develop AR applications, it is necessary to select the methods for detecting and tracking objects. The main frameworks of visual tracking for AR are as follows.

Detection and Tracking

Object detection is first applied to an image and then detected objects are tracked in next incoming images with a tracking by tracking algorithm [START_REF] Pilet | Virtually augmenting hundreds of real pictures: An approach based on learning, retrieval, and tracking[END_REF] [START_REF] Wagner | Pose tracking from natural features on mobile phones[END_REF] . If tracking failed, object detection is again applied to an image for reinitialization.

Tracking by Detection Tracking by detection described in Section 2.2.1 can also be consider as a framework. In this framework, an object is tracked in all incoming images with a detection algorithm [START_REF] Lepetit | Keypoint recognition using randomized trees[END_REF] [START_REF] Ozuysal | Fast keypoint recognition using random ferns[END_REF] . In other words, an object is detected in every frame. Because only detection algorithm is used, a re-initialization problem does not need to be considered.

Unified Approach This approach has recently been proposed [START_REF] Takacs | Unified real-time tracking and recognition with rotation-invariant fast features[END_REF] . The basic idea of this approach is that a keypoint descriptor is used for both matching with a database and tracking between two successive images. First, a descriptor is matched with a descriptor database to detect an object. Once an object is detected, it is tracked by matching keypoints between two successive images with the descriptor. Because the descriptor is compressed into 1 dimensional integer vector, fast keypoint matching between two images is possible.

Additional Sensors

Recently, several sensors have been integrated with a camera to acquire various sensing data. In this section, we introduce the example uses of a accelerometer and a RGB-D camera.

7.1 Accelerometer These days, accelerometers have been integrated into many devices such as mobile phones. From accelerometers, the direction of gravity is estimated and used in several ways. Kotake, et al. proved that pose estimation was simplified using inclination constraint because inclination component of the orientation was known [START_REF] Kotake | A hybrid and linear registration method utilizing inclination constraint[END_REF] [START_REF] Kotake | A fast initialization method for edge-based registration using an inclination constraint[END_REF] . Lee, et al. rectified a captured image into a fronto-parallel FCV2012 view as normalization of a local image patch for keypoint matching [START_REF] Lee | Point-and-shoot for ubiquitous tagging on mobile phones[END_REF] . Kurz and Benhimane rectified feature descriptors to make them more discriminative instead of rectifying a local image patch [START_REF] Kurz | Gravity-aware handheld augmented reality[END_REF] .

7.2 RGB-D Camera Thanks to Kinect from Microsoft, RGB color images and depth images (RGB-D) are captured in real-time. Therefore, a depth camera is incorporated into AR applications.

Park, et al. refined a camera pose with edges extracted from depth images [START_REF] Park | Texture-less object tracking with online training using depth camera[END_REF] . Newcombe, et al. proposed a SLAM framework with a depth camera that can densely mapped and track a camera pose only with depth images [START_REF] Newcombe | Kinectfusion: Real-time dense surface mapping and tracking[END_REF] .

Dataset for Evaluation

To compare a proposed method with existing methods, a benchmarking dataset is necessary for fair comparison. In this section, we introduce some datasets for both detection and tracking.

Detection

This issue is equivalent to widebaseline feature matching because it is important to detect an object under perspective views.

Mikolajczyk Dataset †

This dataset is the most widely used for the evaluation of feature matching between two views [START_REF] Mikolajczyk | A comparison of affine region detectors[END_REF] . In this dataset, several sets of 6 scenes including rich texture or repetitive texture are prepared. They are captured under different conditions such as perspective transformation and blurring.

For each set, ground truth homography matrices are provided. Therefore, the ratio of false positive, false negative and the number of correspondences can be computed for evaluation.

8.1.2 CMU Grocery Dataset † † This dataset is originally designed for evaluating 3D object recognition [START_REF] Hsiao | Making specific features less discriminative to improve point-based 3d object recognition[END_REF] . In this dataset, 620 images of 10 grocery items such as soda cans and boxes in kitchen environments are prepared. The images are captured under perspective views and different lighting conditions with clutter background.

Ground truth 2D segmentations are provided for 500 images. These segmented images can be used as reference objects. For 120 images, 6 DoF camera poses in rodrigues format are provided. Therefore, the accuracy of estimated camera poses can also be evaluated.

Tracking

Tracking is normally evaluated with an image sequences with various camera movement. Recently, several datasets have been developed as follows.

Metaio Dataset † † †

This dataset is designed for the evaluation of planar template based tracking [START_REF] Lieberknecht | Benchmarking template-based tracking algorithms[END_REF] . Four planar textures were captured with five camera motions to generate 40 different image sequences.

The evaluation criterion is the root-mean-square (RMS) distance of four points placed on the diagonal lines of a reference image. The distance is computed † http://www.robots.ox.ac.uk/ ∼ vgg/research/affine/ † † http://www.cs.cmu.edu/ ∼ ehsiao/datasets.html † † † http://www.metaio.com/research/ by projecting points on a test image onto those on a reference image with homography between two images. The ground truth of homography for each image was acquired with fiducial markers and a precisely calibrated robot arm that still computed a camera pose under fast camera motion. In order to avoid the use of fiducial markers for tracking, the markers were interpolated with white. Image borders were also replaced with randomized borders.

In this dataset, the ground truth is not provided because it is necessary to prevent the optimization of parameters in a method for a specific image sequence. Therefore, the users need to submit the result to Metaio. Metaio gives the ratio of successfully tracked images. Note that the ground truth of some images is provided for pose initialization.

8.2.2 UCSB Dataset † † † † This dataset is also dedicated to the evaluation of planar template based tracking (26) . The scope of the dataset is almost similar with Metaio dataset, but more different types of image sequences are included. The dataset includes 6889 frames composed of 96 image sequences with six planar textures.

The ground truth of homography for each image and reconstructed camera poses are provided. Therefore, camera position can also be evaluated in addition to RMS distance as in Metaio dataset.

TrakMark Dataset †5

Compared with the two datasets described above, this dataset focuses on the evaluation of visual tracking for a 3D scene [START_REF] Shibata | An intermediate report of trakmark WG -international voluntary activities on establishing benchmark test schemes for AR/MR geometric registration and tracking methods[END_REF] . Because a 3D model of a scene is provided in some image sequences, model based tracking can be evaluated [START_REF] Petit | Evaluation of model based tracking with trakmark dataset[END_REF] . In addition, SLAM can also be evaluated. This dataset includes image sequences of three different scenes: a small room, an outdoor environment and virtual space.

First scene was captured with a movie camera at the film studio of Japanese period drama. The ground truth provided in this sequence is the position and orientation of a camera measured with several sensors.

As second scene, an outdoor environment was captured with a handheld camera on a sunny day. In this dataset, some image sequences include the ground truth of 2D-3D point correspondences. The 3D coordinates of landmark points are measured with a total station (time-of-flight laser system) and their image coordinates in each image are manually selected.

Last scene is virtual space generated by reconstruction of a real scene. Test images are generated by simulating any camera motion with textured 3D models. Therefore, the ground truth is the transformation matrix from the world coordinate system to the camera coordinate system for each image. Also, textured 3D models are provided.

Conclusion

This paper presented state-of-the-art technologies of object detection and pose tracking for AR applications. † † † † http://ilab.cs.ucsb.edu/tracking dataset ijcv/ †5 http://trakmark.net/

We first explained projection models and pose estimation depending on the shape of objects. Then, we classified and summarized the recent progress of detection and tracking techniques. Also, we introduced some evaluation datasets and evaluation procedures. As described in this paper, the technologies of visual tracking for AR have actively been investigated. However, there is not one perfect method that outperforms others (26) . Because each method has advantages and limitations, it is important to select an appropriate method depending on applications.

Acknowledgements

We would like to thank Francisco Magalhaes and Joao Paulo Silva do Monte Lima from Federal University of Pernambuco for meaningful comments and discussion. A part of this work was supported by a grant-in-aid for the global center of excellence for high level global cooperation for leading edge platform on access spaces from the ministry of education, culture, sport, science, and technology in Japan.