Thierry Poibeau

Mylène Maignant

Frédérique Mélanie-Becquet

Clément Plancq

Matthieu Raffard

Mathilde Roussel

Mathilde Saurat

OuPoCo, the Combinatorial Poetry Workbench

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

OuPoCo, the combinatorial poetry workbench (L'ouvroir de poésie combinatoire)

Thierry Poibeau, Mylène Maignant, Frédérique Mélanie-Becquet, Clément Plancq, Matthieu raffard, Mathilde Roussel, Mathilde Saurat

• Laboratoire Lattice CNRS & École normale supérieure/ PSL & Université Sorbonne nouvelle / USPC 45 rue d'Ulm 75005 Paris {firstname.lastname@ens.fr}

• Atelier Raffard-Roussel, Paris raffard.roussel@gmail.com Oupoco (L'ouvroir de poésie combinatoire) is a project taking inspiration from Raymond Queneau's book Cent mille mille milliards de poèmes, published in 1961. Queneau's book is a collection of ten sonnets which verses can be freely recombined to form new poems. The book can be seen as composed of ten sheets, each separated into fourteen horizontal bands, each band carrying a verse on its front. The reader can choose, for each verse, one of the ten versions proposed by Queneau. The ten versions of each verse have the same scansion and rhyme, which ensures that each sonnet thus assembled is regular in shape [START_REF] Queneau | Cent mille milliards de poèmes[END_REF].

It would be tempting to develop a computer-based version of Queneau's work, but Queneau's book is still under copyright, and it is by definition limited to its ten original sonnets. To overcome this problem, we developed the Oupoco project, aiming at proposing a sonnet generator based on the recombination of a large collection of 19th century French sonnets. The challenge is thus more complex than the one proposed originally by Queneau since our sonnets do not have the same scansion and rhyme. From this point of view, even if the project is intended to generate new sonnets, it is largely based on the development of analysis tools able to identify the scansion, the rhyme and the structure of the original sonnets. It is thus very different from the numerous projects dedicated to the pure generation of poetry, being with symbolic [START_REF] Gervás | Computational Modelling of Poetry Generation[END_REF] or neural methods [START_REF] Ghazvininejad | Hafez: an Interactive Poetry Generation System[END_REF][START_REF] Van De Cruys | La génération automatique de poésie en français[END_REF] (among many others).

Oupoco is currently based on a collection of 788 sonnets from 16 authors from the 19 th century, and this database is regularly expanding. Each sonnet is encoded in a XML format along with related metadata, and a TEI version of the database is available. The project requires to get access to a formal representation of rhymes [START_REF] Beaudouin | Mètre et rythme du vers classique[END_REF]. In order to do this, the first step is to get a phonetic transcription of the last word of each verse, but this is not enough: for example, aimé and aimée have the same phonetic transcription, but do not rhyme, according to French rhyming rules (feminine and masculine do not rhyme according to the classical rules of French poetry); there are also cases where the phonetic transcription diverges but words actually rhyme (for example with sounds like [e] and [e]). A series of rules had thus to be defined to get a proper analysis of rhyme from the phonetic transcription of the last word of each verse. The generator uses this analysis to produce random sonnets, with different possible structures, respecting the rules of French versification (the code and the resources used, especially the sonnet database, are open source and freely available for research, see: https://github.com/clement-plancq/oupocoapi).. A series of "side products" have been produced from the project, including:

• a website (https://oupoco.org/):

• a bot posting on Twitter (https://twitter.com/oupoco_bot):

• and a "poetry box" (la boîte à poésie), a portable version of the original idea that can be demonstrated in public events (based on Raspberry Pi components). Through these devices our goal is to reach a wider audience and engage people to reconnect with poetry.

The main interest of the project is to present French poetry through a new and original setting. With our system, poetry is not any more just a literary genre [Derrida and Ronnel, 1980], but a dynamic object that can be manipulated and experienced. For lots of people, poetry is seen at best as something related to school years, at worse as something boring and uninteresting from the past. Our new setting, in itself, makes it possible to show that playing with poetry can be fun. Our setting puts in perspective the notion of text coherence [START_REF] Reinhart | Conditions for Text Coherence[END_REF], since the result of the generator can be more or less satisfactory from a semantic point of view.

This has two consequences. The first one is related to interpretation: because the machine produces structurally impeccable sonnets, the experiencer is unconsciously encouraged to find coherence in them, simply because we are used to coherence in our everyday life and because incoherence is bewildering. The second consequence is a frequent need for the experiencer to go back to the original poem, to see where from a given verse originates (tooltips always allows the experiencer to go back to the original sonnet where a verse has been extracted). The project is thus not just a sacrilege game over venerated texts, but a way to make people experience and rediscover poetry.

During the presentation, we will detail the technical aspects of the system, and we will examine some examples automatically produced.

Acknowledgement

This work has received support of Translitterae (Ecole universitaire de recherche, program "Investissements d'avenir" ANR-10-IDEX-0001-02 PSL* and ANR-17-EURE-0025) and the "Investissements d'avenir" program, reference ANR-19-P3IA-0001 (PRAIRIE 3IA Institute).


Laurent Warlouzet

THE IMPLEMENTATION OF THE SINGLE MARKET PROGRAMME (1985-92) THE EXAMPLES OF THE CAR EMISSION AND OF COMPETITION POLICY

This contribution will focus on the implementation of the Single Market programme between its definition in the Single Act in 1986, and its "opening" in 1993. I will argue that the Single Market was a compromise between different visions of Europe, and not solely a neoliberal project. In doing so, I will use a typology that differentiates between three types of economic policies: socially-oriented, neomercantilist, and market-oriented, with neoliberal policies being a sub-group of the final category. A few examples, including legislation on mergers and car pollution, will be explored in-depth by way of illustration.

Treaty. 2 Even if it was eventually replaced at the forefront of the European integration dynamic by the project of European Monetary Union, the removal of controls at many border posts in late 1992 remained a major breakthrough. In his inaugural speech before the European Parliament in January 1985, Delors announced that this would become a reality in 1992, with his prediction becoming reality on schedule.

In contrast to the Common Market, which was completed in 1968 after the removal of internal customs duties and the adoption of a common external tariff, the notion of a Single Market included the removal of all non-tariff barriers. There were many of them, ranging from technical barriers to national commercial laws. A large number of national laws had to be harmonized in order to remove such obstacles, hence the need to adopt qualified majority voting for Article 100 EEC, which addressed the convergence of national regulations. The principle of mutual recognition popularized by the Cassis de Dijon ruling of 1979 was not enough to create a Single Market on its own, as it contained four exemptions, which is to say four types of legislation that had to be harmonized ("the effectiveness of fiscal supervision, the protection of public health, the fairness of commercial transactions, and the defence of the consumer"). 3 The Commission recognized the limitations of Cassis de Dijon early on, [START_REF] Warlouzet | Governing Europe in a Globalizing World. Neoliberalism and its Alternatives following the 1973 Oil Crisis[END_REF] with most of its proposals subsequently being stuck in the Council during the early 1980s due to the unanimity rule.

Beyond the harmonization of standards, the notion of a Single Market also includes some form of tax harmonization directly linked to the removal of border controls, such as those dealing with the value added tax and excise duties, which were the primary source of verifications (exemption and then new taxation) during border controls. By extension, it entailed the development of common tools for managing the Single Market, such as competition policy, notably through the Europeanization and liberalization of the air transportation and telecommunication sectors, which began in 1987-88, along with public procurement. More generally, the completion of the Internal Market encompassed the four freedoms of movement for goods, services, capital, and citizens. Article 13 of the Single European Act (SEA) stated that: "The internal market shall comprise an area without internal frontiers in which the free movement of goods, persons, services and capital is ensured in accordance with the provisions of this Treaty."

The adoption of the Single Market Programme in the 1986 Single Act, combined with the adoption of qualified majority voting at the Council for the removal of most non-tariffs barriers, unleashed a sustained momentum. Article 13 SEA specified that "The Community shall adopt measures with the aim of progressively establishing the internal market over a period expiring on 3l December 1992," thus setting in stone the deadline of 31 December 1992 set by Jacques Delors in his keynote speech to the European Parliament on 14 January 1985.

Based on various materials collected in national and European archives, and in keeping with the recent enlargement of the historiography of European integration towards new arenas,5 this article will argue that the implementation of the Single Market Programme was not unequivocal: while it was dominated by a market-oriented approach, it encompassed other dimensions including neoliberal, social, and neomercantilist orientations. The first part of this contribution will define these categories in the context of the Single Market, and the final two sections will focus on two examples of conflict between different visions of economic Europe: the 1989 car-emission directive, and competition policy regarding state aid and mergers.

A multifaceted Single Market Programme

Article 13 SEA gives an extensive definition of the internal market. The push to build it translated not only into directives harmonizing standards, but also into directives touching on public procurement, capital flows, the harmonization of Value Added Tax (VAT) regimes, and the "television without border" directive, all of which were adopted before the 1993 deadline. 6 The broad definition of the Single Market promoted by the European Commission was also present in the "Cecchini Report," named after the former Deputy Director-General for the Internal Market at the European Commission, Paolo Cecchini. This report, which was commissioned and disseminated by the Commission, completed an in-depth evaluation of the estimated benefits of the Single Market, which were estimated at gains of approximately 5% for the gross national product, i.e. approximately ECU 200 billion. He concluded with four points:

-"business must respond to the challenge and seize the new opportunities on offer. Corporate management should also seek to make industrial relations less conflictual, encourage employee involvement in the life of the enterprise, and ensure that workers share in the jointly achieved productivity gains; -competition policy must be effectively enforced; -the distribution of gains must be fair, as must be the distribution of cost; -monetary stability and the necessity to strengthen ... the European Monetary System."

Hence, according to this definition, which was later endorsed by the Commission, the Single Market extended to competition and monetary policy, and contained a dimension of fairness and harmonious industrial relations.

The single market is actually multifaceted, since the Single Act left ample room for divergent interpretations. On the whole, one can argue that the implementation of the Internal Market Programme was dominated by a market-oriented approach, but that this approach nevertheless was multi-faceted, thereby triggering conflicts within the Commission. Since the Single Market program covered many different policies ranging from trade to taxation, a huge number of different facts, concepts, and notions must be covered. In order to facilitate comparison across countries and move beyond the mere juxtaposition of facts, the various conceptions of the internal market program have been grouped into three models for economic policy: social, neo-mercantilist and market-oriented. 7 Supporters of a social Europe seek to protect vulnerable groups such as the poor and minorities, for instance women. More broadly, they are willing to tackle the negative externalities of markets that diminish quality of life. "Social policy" thus includes measures of legislation and redistribution in terms of social insurance, working conditions (including the democratization of companies), health, environmental protection, regional solidarity, and so on. 8 A social Single Market is based on high norms, in accordance with article 100-A-3 of the Single Market: "The Commission, in its proposals envisaged in paragraph 1 concerning health, safety, environmental protection and consumer protection, will take as a base a high level of protection." German Länder were especially attentive to ensuring that future EEC norms do not downgrade earlier DIN standards. 9 Neo-mercantilist policies combine mercantilism's aggressive stimulation of national industrial potential with the insertion into the international free-trade order (hence the prefix "neo"). Blatant protectionism was no longer possible beginning in 1960s, although more discreet measures such as state aid, cartels, or technical norms favouring national producers are still possible. A neomercantilist Single Market would promote norms favourable to European industrialists, and possibly discriminate against non-European producers. This neomercantilist approach was particularly favoured by the French government, and when coupled with a more Europeanized angle, by Delors as well. 10 Lastly, "market-oriented" policies strove to foster free-market dynamics, which according to the neoclassical doctrine are believed to unleash growth. A market-oriented Single Market focuses on removing obstacles rather than erecting new constraints on business. More generally, this translated into a debate as to whether more regulation was needed via harmonization towards higher standards-hence the paradox captured by the expression "freer markets, more rules" 11 -or whether a broad interpretation of mutual recognition would lead to less legislation and constraints for trade. The latter solution ran the risk of a "race to the bottom" in terms of standards. It embodied the "neoliberal" dimension of EEC/EU 7 More information on this typology can be found in Laurent Warlouzet, Governing Europe, op. cit. chapter 1. policies, which fostered a radicalization of market-oriented policies, especially by emphasizing a retreat from the welfare state. 12 This vision was embodied at the time by British Prime Minister Margaret Thatcher's crusade for "deregulation," which was at the heart of the British memorandum from March 1985 entitled "The Creation of Wealth and Employment in the Community." [START_REF]The creation of wealth and employment in the Com-munity[END_REF] It requested a report on "the burden imposed on businesses by existing Community legislation and the way to reduce it [and] take business costs into account in future legislation," and on decreasing some welfare state expenditures. The British prime minister tried to coordinate with the Belgian and Dutch governments (of Martens and Lubbers, respectively), but to no avail, as both of these countries were more supranational. [START_REF] Warlouzet | Governing Europe[END_REF] These models are useful because they overcome the vocabulary differences that often hamper comparison; they also shed light on conflicts within EEC institutions, as exemplified by the debates surrounding the car-emission directive and competition policy.

Environment and Industrial Interests: The Car-emission Directive (1989)

The environment became a new field of public policy in the 1970s in the West, and within the EEC in particular. [START_REF] Schulz-Walden | Between National, Multilateral and Global Politics: European Environmental Policy in the 1970s[END_REF] It therefore represented a sizeable part of the Single Market programme. The European Parliament played an important role in this field thanks to the new cooperation procedure established in the Single Act. This Treaty included environmental policy within the range of EEC competences thanks to a whole new chapter. It inserted certain provisions over environmental protection within the remit of article 100-A-3, as long as they were directly related to the Internal Market Program. This is especially relevant since they could be adopted by qualified majority voting instead of requiring unanimity. The Commission usually supported the European Parliament in its extensive interpretation of article 100 in order to put additional pressure on the Council, although the Commission and the European Parliament were not always in agreement. For example in October 1987, the Commission refused to consider that radioactivity in food (a follow-up to the Chernobyl disaster) fell under article 100 A-as argued by the European Parliament's rapporteur, the German Social Democrat Mrs. Undine-Uta von Blottnitza-and instead preferred article 31 Euratom. 16 The "car-exhaust directive" was singled out by Nicole Fontaine, a former president of the European Parliament and a member of the European Parliament (MEP) in those days, as one of the most important battles in the assertion of the European Parliament. [START_REF] Fontaine | [END_REF] Aimed at diminishing the most harmful car emissions, namely those linked to leaded petrol, it was a major stepping-stone in the assertion of both EEC environmental policy and the European Parliament in implementing the Single Market.

The origins of this debate are twofold. Those supporting a social Europe stressed the causal link between car emissions and acid rain, and thereby the destruction of forests in Central and Northern Europe, while neomercantilist leaders insisted on the need for European cars to follow tighter US standards in order to keep this market open for their exports.

The grassroots movement against "Waldsterben" gained powerful momentum in Germany but not in France, because the former was more affected by acid rain than the latter, and because ecological movements were stronger East of the Rhine. In Germany they were associated with the post-1968 movement, whereas in 1960s and 1970s France they were still taintedaccording to Birgit Metzger and Laurent Schmit-with an anti-modernization spirit reminiscent of the Vichy era. 18 Acid rains were not caused by led in petrol but by the emission of two gases, sulfur dioxide and nitrogen oxide. One of the main emitter of nitrogen oxide were cars, and catalytic converters were the main tool to reduced those emissions. However, catalytic converters requried unleaded petrol. Since acid rain was in particular a problem in Germany, Bonn was one of the main proponents to introduce EEC legislation aimed at promoting unleaded petrol and catalytic converters. In Germany, car manufacturers also became convinced that it was in their interest to follow tighter rules. The mobilization against car emissions also affected the United Kingdom. 19 In France the opposition to tighter emissions was driven by neomercantilist concerns. If legislation on unleaded petrol became law, carmakers would have to add a catalytic converter to their cars. While the price of these catalytic converters and the loss of motor power they entailed were relatively negligible for expensive cars, such as those produced in Germany (with the exception of Volkswagen), they were huge for small cars (such as those produced by French and Italian carmakers). Moreover, German carmakers had invested in this new technology for quite some time, while their French counterparts remained more conservative in this regard. Negotiations at the Council of Ministers were thus stalled by the French government, thereby delaying an agreement in order to protect its car industry. Thereafter, a high-level French-German political rapprochement between Mitterrand and Kohl softened this opposition. A compromise was struck at the Council in March and June 1985, whereby the French government secured less constraining norms for mid-sized and smaller cars (i.e., those massively sold by French carmakers). 20 The adoption of the directive was blocked by a Danish veto (for other reasons) until July 1987. 21 The new procedures of the Single Act entered into force at this time, making it possible to circumvent unanimity. The Council eventually struck an agreement on 21 July 1987 by qualified majority, voting on a new limitation for motors with different standards for large (powered by a motor of more than 2 litres), intermediate (between 1.4 and 2 litres), and small cars (less than 1.4 litres). Some decision-makers considered this agreement imperfect in terms of competitiveness. Several member of the European Parliament "pointed out that the maximum emission levels proposed by the Council were the highest in the world and thus constituted a serious handicap to the competitiveness of the European Industry." 22 From a neomercantilist perspective, adopting low standards would actually make it more difficult to export to non-EEC markets with higher standards, such as the US or Sweden. In the end, a first directive was adopted by the Council on 3 December by qualified majority voting. It established standards close to those in the US, except for the smallest cars, for which only an intermediate standard was adopted in 1989.

The Commission therefore announced a second directive on small engines to complement the first one. 23 A major debate unfolded surrounding this second directive. On 10 February 1988, the Commission issued its draft second directive for cars with motors smaller than 1.4 litres. The EEC Council discussed it and adopted a so-called "Common position," which would serve as the basis for discussions at the European Parliament. This body debated the draft directive on 13 September 1988 as part of a first reading, with the German SPD MEP Kurt Vittinghof authoring the report on the draft directive. 24 He believed that the Council had taken a "half-hearted and industry friendly" stance, chiefly because the proposed standards were still too lenient. He stressed that car emissions played a role not only in "dying forests," but also in damage to public monuments and public health, thereby widening the issue. Other MEPs, such as the British Labourite Carol Tongue, the German Social Democrat Albert Siegbert, and the Belgian Green François Roelants du Vivier, went even further by directly or indirectly challenging the lobbying of French carmakers, in particular Peugeot CEO Jacques Calvet. Calvet became an early and leading voice in the French media for Eurosceptic arguments that the EEC posed a threat to French neomercantilism. The situation was further complicated by many Danish and Dutch MEPs, who called for even more stringent caps.

Copenhagen threatened to take unilateral measures, and the Commission considered accusing the Danish government of hindering the free flow of goods through its stricter national car emission standards! 25 The commissioner in charge of this regulation, the British Labour member Clinton-Davies, nevertheless reinstated the Commission's original position. In accordance with the Council, he rejected the European Parliament's amendment for tighter emission standards. A few months later, in December 1988, the EEC Council logically adopted a Common position that still ignored the European Parliament's call for a stringent cap. After further discussion at the Council, the text returned to the European Parliament on 11 April 1989, but the context had changed in the meantime. The Commission was now represented by a new Commissioner for the Environment, Carlo Ripa di Meana, a former MEP and pioneer of environmental activism in Italy. He proved more willing to act than Clinton-Davies, for he proposed anticipating the adoption of the new standards. 27 The rapporteur Vittinghof actually drew applause when he praised the new commissioner during the debate in plenary session. [START_REF]PE2_AP_DE![END_REF] In his speech during the plenary session, Ripa di Meana underscored what he considered to be a "watershed in the history of Community policy over environmental protection." This was linked to the Single Act, which "built [environmental protection] into the Community's other policies." The ensuing discussion followed a predictable pattern, with constant criticism of the lobbying by the French carmaker Peugeot. MEPs from various political groups stressed the importance of rejecting the Council's common position, should the Commission refuse to accept the amendments. [START_REF] Euha | [END_REF] Interestingly, the debates also led to a broader discussion on environmental policies, including new concepts. Siegbert Alber, a German Social Democrat, referred to the "polluter pays principle," a concept coined by the OECD in 1970, and later taken up by early Green activists in the EEC beginning in 1972. [START_REF] Meyer | Who should pay for pollution? The OECD, the European Communities and the emergence of environmental policy in the early 1970s[END_REF] Another German MEP, Kurt Vittinghof, stressed the issue of "global warming," making reference to a meeting of experts in Turin in January 1989, who considered car emissions to be "one of the main causes of climatic change." [START_REF]PE2_AP_DE![END_REF] MEPs eventually adopted the amendments by a large majority, [START_REF]European Parliament archives[END_REF] which were then included by the Commission in a new draft proposal. The Council ultimately struck a compromise in June 1989, with Directive 89/491/EEC from 17 July 1989. 33 In this case implementation of the Single Market was characterized by an emphasis on Social Europe (in the sense of environmentally-friendly). It could muster support by relying not only on environmental concerns, but on industrial ones as well (the need to follow norms already adopted outside the EEC).

The Neomercantilist Delors vs. the Neoliberals Sutherland and Brittan

The creation of a unified Single Market entailed monitoring private non-tariff barriers: if companies could thwart the removal of trade barriers by market sharing via cartels, or by dominating it via abuse of dominant position, or by receiving excessive state aid, then the benefits of trade liberalization for consumers would be wiped out. This task of monitoring private practice was entrusted to the European Commission, which has implemented EEC competition policy since the Treaty of Rome. This treaty, which created the EEC, established provisions on competition policy including innovative monitoring of state aid, although they were not firmly implemented during the first thirty years. However, beginning in the 1980s competition policy became one of the flagship policies of the EEC/EU. It became more assertive in monitoring state aid, and enlarged its scope to new fields such as the control of concentration, through merger regulations in 1989, [START_REF] Warlouzet | The Centralization of EU Competition Policy: Historical Institutionalist Dynamics from Cartel Monitoring to Merger Control (1956-91)[END_REF] the directive on the liberalization of air transport in 1987, [START_REF] Kassim | Air Transport and the European Union. Europeanization and its Limits[END_REF] and regulations concerning telecommunications in 1988. [START_REF] Thatcher | Internationalisation and Economic Institutions: Comparing the European Experience[END_REF] This evolution was supported by a context favourable to market-oriented ideas. During the 1980s, regulation of the market by competition policy rules replaced direct state management of markets through price and industrial policy, on the European level as well as that of many Western European countries. [START_REF] Warlouzet | Governing Europe in a Globalizing World[END_REF] Jacques Delors had a somewhat ambiguous position towards EEC competition policy. He was broadly supportive, as in his groundbreaking speech of January 1985, where he emphasized the need to get rid of "obstacles to healthy competition." [START_REF]The thrust of Commission policy[END_REF] He stated that "competition can kill competition if the market does not permit fair contest between the different rivals," therefore national laws had to be harmonized to a certain extent. Yet his vision was not purely marketoriented, as he integrated a neomercantilist perspective by calling for the development of a common industrial policy "instead of the costly and ineffective escalation of national aid and incentives." His aim was to improve industrial policies by Europeanizing them, rather than exporting French dirigisme.

While the literature usually links the reinforcement of EEC competition policy to the Single Market Programme, [START_REF]For example John Gillingham, European Integration[END_REF] this domain was actually left largely untouched by the Single Act Treaty. The articles of the 1957 Rome Treaty addressing this domain remained in place. Competition policy was mentioned only in relationship to other policies (such as cohesion policy in article 130f-3). As a result, the rise of EEC/EU competition policy did not derive from automatic interpretation of the Single Act, but instead from the activism of competition policy commissioners, in this case Peter Sutherland (1985-89) and Leon Brittan (1989-1993).

As a French Social Democrat, Delors was sometimes disturbed by the neoliberal tendencies of his two commissioners for competition policy. In their recent accounts, both Delors and Sutherland believed that they got along well, since they both shared an ambitious agenda for European integration, although they also recognized specific conflicts over state aid. [START_REF][END_REF] The archives reveal that one such instance involved Boussac, the largest textile firm in France. Under the insistence of Sutherland, the Commission targeted very substantial French aid to the firm totalling close to FF 1 billion. [START_REF][END_REF] French officials argued that this powerful company was on the verge of bankruptcy, and that the subsidy was justified in order to avoid massive layoffs in regions of Northern and Eastern France already crippled by the industrial crisis in other sectors of traditional manufacturing (coal mining, steelmaking, shipbuilding). But Sutherland stressed that since Boussac was an export firm, the aid would affect intra-European trade. In any event, since the subsidies were granted without a corresponding restructuring plan, they were clearly illegal. 42 The bold Irish commissioner was also motivated by the clumsiness of French officials, who blatantly ignored EEC rules on state aid, and were unwilling to disclose information. 43 Other countries also helped their textile industry, notably Belgium with its Claes plan also targeted by the Commission, although the most high-profile case was the French one.

During internal debates at the Commission, Sutherland proposed requesting a massive repayment of FF 999 million by the company. This triggered a hostile reaction from the Frenchman François Lamoureux, a prominent member of Delors's cabinet, who estimated that there was an "unprecedented disagreement" within the Commission on this question. 44 Lamoureux was a staunch French Socialist who later became deputy head of Edith Cresson's cabinet when she was the French Prime Minister under the Socialist government (1991-2). More precisely, two issues sparked controversy within the Commission. First, many Commission officials contested the Directorate General for Competition's calculations for the illegal aid. The Directorate General in charge of Industrial Affairs, DG III, followed a more neomercantilist line of reasoning, insisting on the importance of taking into account the intensity of Boussac's restructuring, and the problem of international competition. 45 Second, commissioner Sutherland dared to challenge evidence provided by a national government, an accusation that was extremely controversial from a political point of view. Sutherland compromised in the end, securing the Commission's support to sanction the French government, but settling for a repayment of FF 338 million. 46 Interestingly, the neoliberal vision embodied by Sutherland annoyed other Social Democrat commissioners. This demonstrated that this was not just a matter of nationality, with the Frenchman Jacques Delors being concerned by the fate of a large French company. In July 1986, when the College of Commissioners discussed Sutherland's draft directive seeking to impose stricter control of state aid for shipbuilding, he faced opposition from multiple commissioners, all of whom belonged to the centre-left (with the exception of the Christian Democrat Lorenzo Natali, probably because Italy's large nationalized industries were often the target of the European Commission): the Spanish Socialist Manuel Marin (Social Affairs), the Italian Socialist Carlo Ripa di Meana (Institutions and Culture), the Greek Socialist Grigori Varfis (Regional Policy), and the British Labourite Stanley Clinton-Davies (Transport). 47 In December 1986, the Italian Socialist Carlo Ripa di Meana accused Sutherland of being "too repressive towards European industry." 48 All of these commissioners estimated that competition policy should also take into account social and neo-mercantilist considerations.

Later on, the conflict with the neoliberal commissioner for competition intensified under Leon Brittan, the British Thatcherite who held the Commissionership for Competition from 1989 to 1993. [START_REF] Leon Brittan | Les commissaires européens. Technocrates, diplomates ou politiques ?[END_REF] The most famous conflict occurred in 1991, when Brittan decided to ban the merger between two aircraft companies, with French-Italian ATR due to take control of the Canadian De Havilland. [START_REF] Pollack | The Engines of European Integration. Delegation, agency, and agenda setting in the European Union[END_REF] The case was sensitive for a variety of reasons. From the institutional point of view, it was the first time the Commission used its power to ban concentration between companies since the merger regulation was adopted in late 1989. The merger made sense from the economic point of view, since other competitors existed both within Europe (British Aerospace and Fokker in particular) and without. From the political point of view, this operation was hailed as a symbol for an EEC industrial policy in high technology seeking to create European champions that could compete with mightier US firms. Indeed, it was the French-Italian firm ATR, itself an example of European industrial cooperation, that bought its Canadian competitor De Havilland. This operation embodied a new form of Europeanized neomercantilism in high technology, an approach that the British commissioner sought to deter. Brittan opposed it on competition grounds by adopting a narrow definition of the relevant market, in order to demonstrate that the new companies would have a dominant position. [START_REF] Frédéric | Droit européen de la concurrence et efficience économique[END_REF] The decision triggered reservations even within DG Competition. [START_REF]On the reservation of DG Competition[END_REF] During the debate with the College of Commissioners, Delors opposed Brittan, but ultimately abstained when he saw that he would lose the case to a coalition of mostly centre-right commissioners. [START_REF] Ross | Jacques Delors and European Integration[END_REF] Delors's position was logical, for he had long favoured an EEC industrial policy in high technology that combined neomercantilism with international free trade. [START_REF]On Delors's commitment to develop an EEC industrial policy in high technology : Laurent Warlouzet[END_REF] As a result, while Delors was generally supportive of strengthening EEC policies in general, and EEC competition policy in particular, he opposed the neoliberal orientations of Sutherland and Brittan, sometimes with the support of other Social Democrat commissioners, albeit with limited success.

Conclusion

The European Internal Market Programme was implemented as a mostly market-oriented project, but with visible neoliberal, social, and neomercantilist features. This was particularly true for Delors, who combined socially-oriented, neomercantilist, and market-oriented visions of Europe. This compromise can be seen in the adoption of the car-emission directive in 1989 with strong support from the European Parliament, which acquired a higher profile in EEC decision-making thanks to the Single Market Programme. The neoliberal approach nevertheless quickly gained traction, as demonstrated by the ATR/De Havilland example. This triggered internal conflicts within the Commission, particularly between Delors and competition policy commissioners. This neoliberal orientation became even more prominent from the 1990s onwards, and is one explanation for the current crisis in legitimacy faced by the EU. Paradoxically, this was recently exemplified by the Brexit vote, even though the British government was at the vanguard of the neoliberal transformation of Europe.

18

  Birgit Metzger et Laurent Schmit, "Shades of Green: Ökologische Modernisierung im deutsch-französischen Vergleich (1970-1990)", in Martin Bemman, Birgit Metzger, Roderich von Detten (ed.), Ökologische Modernisierung. Zur Geschichte und Gegenwart eines Konzepts in Umweltpolitik und Sozialwissenschaften, Francfort: Campus Verlag, 2014, pp. 257-286. 19 Martin Chick, "The changing role of space and time in British environmental policy since 1945", Revue française d'histoire économique, 1, 2015, pp. 72-89. 20 European Parliament archives, PE2_AP_RP!ENVI.1984_A2-0132!880010EN, Report on the proposal from the Commission of the European Communities for a Council directive amending Directive 70/220/EEC on the approximation of the laws of Member States relating to measures to be taken against air pollution by gases from the engines of motor vehicles (European emission standard for cars below 1.4 litres), Com (87) 706, rapporteur: K. Vittinghof, 29 June 1988, document A 2-0132/88; British archives, PREM 19/1490/1, brief, Environmental Issues, 26 March 1985. 21 European Parliament archives, PE2_AP_RP!ENVI.1984_A2-0132!880010EN, Report on the proposal from the Commission of the European Communities for a Council directive amending Directive 70/220/EEC on the approximation of the laws of Member States relating to measures to be taken against air pollution by gases from the engines of motor vehicles (European emission standard for cars below 1.4 liters), Com (87) 706, rapporteur: K. Vittinghof, 29 June 1988, document A 2-0132/88.

  25 EUHA, European Commission archives, special minutes of the meeting of 14 December 1988. 26 European Parliament archives, PE2_AP_RP!ENVI.1984_A2-0026!890020FR, Recommendation by the Committee on Environment, Public Health and Consumer Protection on the Common Position of the Council with a view to the adoption of a directive amending Directive 70/220/EEC on the approximation of the laws of the Member States relating to measures to be taken against air pollution by gases from the engines of motor vehicles (European emission standards for car below 1,4 litres), 28 March 1989, part A (document A2-26/89/Part A) and part B (document A2-26/89/Part B).

8

  See Aurélie Andry's recent PhD dissertation: Aurélie Andry, Social Europe in the long 1970s. The Story of a Defeat, PhD diss., European University Institute (Florence), 2017.

9 Laurent Warlouzet, Governing Europe, op. cit., p. 183. 10 Laurent Warlouzet, Governing Europe, op. cit., pp. 192-4 and chapter 8. 11 S.K. Vogel, Freer Markets, More Rules : Regulatory Reform in Advanced Industrial Countries, Ithaca: Cornell UP, 1996.

  26 22 EUHA, Florence, GSPE 77/2379, note on the Environmental Committee, session of 30 September 1987-1/2 October 1987.

	23 EUHA, GSPE 77/2524, political report, 16-20 November 1987.
	24 European Parliament archives, PE2_AP_DE!1988_DE19880913-169900FR, debates in plenary session on 13
	September 1988.

The bibliography on the Single Market programme in the 1980s that is not based on an archival approach includes: Michelle Egan, Constructing a European Market, Oxford: Oxford University Press, 2001; Gilles Grin,

Kiran Klaus Patel, "Widening and deepening? Recent advances in European Integration History," in Neue Politische Literatur,

64, 2, 2019, pp. 327-357.6 For further details on this legislation, see Laurent Warlouzet, "The internal market and competition", in Vincent Dujardin, Éric Bussière, Piers Ludlow, Federico Romero, Dieter Schlenker and Antonio Varsori (eds.), The European Commission, 1986-2000. Histories and memories of an Institution, Luxembourg: Publications Office of the European Union, 2019, pp. 257-280; for the TV Without Borders directive, see also Kiran Klaus Patel's contribution in this volume.

This classification is different from the one used in the history of ideas, since the term "neoliberal" as defined after the Lippmann conference was much broader, and therefore not applicable for a cross-country comparison. See, among others, Hagen Schulz-Forberg and François Denord's work on the history of neoliberal ideas.

On commissioner Ripa di Meana's inclination for environmental issue, see interview of François Roelants du Vivier by Laurent Warlouzet in Brussels on 18 October 2017.

EU archives, European Commission, BDT 323/93/210, note on the meeting of commissioner, 4 July 1986, note on the meeting of the chef de cabinet, 11 July 1986.


J Randrianandrasana

P Callet

L Lucas

A SIX-FLUX TRANSFER APPROACH FOR EFFICIENT LAYERED MATERIALS RENDERING

To achieve high fidelity appearances, we propose to isolate light having undergone one or more scattering events in a medium (secondary flux) from light not scattered by any medium in the structure (primary flux). Moreover, as a significant amount of light might be scattered back with scattering media, we propose to split the secondary flux into forward and backward contributions.

Guo et al. 2018

Based on this representation, we compute the shapes of the outgoing primary and secondary flux due to a layer of the stack as weighted sums of HG lobes. Thanks to HG convolution properties, the asymmetry parameters of the resulting lobes can be computed with the same transfer matrix formalism and multiple scattering matrix operators.

Many objects of our everyday life include scattering volume layers (dust deposition, weathering, pigments, ...). While layered materials composed of rough interfaces are well handled by state-of-the-art efficient rendering approaches, participating media layers remain poorly supported. In practice, this incurs severe energy losses yielding inconsistent dark appearances with increasing volume scattering.

PROBLEM

Related Work / Motivation

OVERVIEW

RESULTS

REFERENCES THE SIX-FLUX APPROACH

[1] Wenzel Jakob, Eugene d'Eon, Otto Jakob, and Steve Marschner. A comprehensive framework for rendering layered materials. ACM Transactions on Graphics (ToG), 33(4), 2014.

[2] Yu Guo, Miloš Hašan, and Shuang Zhao. Position-free monte carlo simulation for arbitrary layered BSDFs. ACM Transactions on Graphics (ToG), 37(6), 2018.

[3] Laurent Belcour. Efficient Rendering of Layered Materials Using an Atomic Decomposition with Statistical Operators. ACM Transactions on Graphics (ToG), 37(4), 2018.

We overcome these limitations with an efficient solution based upon a transfer matrix modeling. Under this formalism, each volume and interface is described through a lightweight matrix, layering operations reduce to simple matrix products, and total flux accounting for multiple scattering are obtained thanks to matrix operators.

To be fully compliant with the matrix formalism, we propose to approximate light-matter interactions within the structure with Henyey-Greenstein (HG) phase function convolution products as they reduce to simple asymmetry parameters multiplications.

Accurate solutions: Highly accurate methods have been proposed in recent years. However, these approaches reveal impractical for low-time budget rendering due to expensive per-material precomputations [1] or because of additional variance due to their stochastic nature [2].

Efficient methods: Belcour [3] recently introduced a low computation cost multi-lobe approach. To this end, the author introduces a low-order statistical representation for light-matter interactions and derives new adding equations for the framework. However, scattering volumes are poorly supported as the method does not account for back-scattering and resorts to single scattering approximations to avoid expensive doubling operations. Unfortunately, the framework introduced by the author can not be easily extended to handle both forward and backward propagating flux and scattering volumes of arbitrary depths.

RELATED WORK

Belcour 2018 Ours

In this form, generic matrix operators for primary and secondary reflectances accounting for internal multiple scattering are easily derived based on the BRDF boundary conditions. We obtain the transfer matrix of a homogeneous participating medium by approximating the transport occurring in an infinitesimally thin slab and derive the matrix for any arbitrary depth with the exponential matrix method. In the case of an interface, the transfer matrix further simplifies as no interaction happens between primary and secondary flux.

Accounting for the upward and downward directions of propagations in the structure, we thus describe the light distribution at any depth of the structure as a six-flux vector. The net balance relating the total flux sitting on each side of any stack component of the structure (interface, volume layer, or any combination of them) takes a general order-six matrix form.

To compute the shapes of the outgoing lobes with the transfer matrix formalism, we further approximate each light-matter interaction in the structure as HG phase functions convolution as they simply express as asymmetry parameters products. Thus, we describe each lobe through an (energy, mean, asymmetry) statistical representation. Participating media are naturally handled as they are usually described with this phase function. In the case of interface components, we provide a simple analytical fit for GGX-based rough interfaces.

Starting from the incident medium, we approximate the BRDF of the stack as a mixture of forward and backward GGX lobes sharing the same mean directions following the same iterative approach than previous work [3].

We implemented our approach in the Mitsuba renderer. All the results shown in this section use the path integrator. Our approach handles stacks of rough interfaces with visual results comparable to state-of-the-art efficient methods [3]. While the latter suffers from drastic energy losses, our approach provides results close to the ground truth, even with strongly backscattering media. Additional computational costs are mainly due to the order-six matrix products Ours Guo et al. and additional lobes calculus. While stochastic approaches [2] introduce significant variance and computation cost with increasing volume scattering, the six-flux approach provides high fidelity results with a low sample budget. As the main limitation, only isotropic interfaces are currently supported due to the underlying HG representation. Future work will investigate if the approach is suitable for interactive rendering on the GPU.

Ours


N Courilleau

Y Remion

L Lucas

SIMULATING DEPTH PERCEPTION IN VIRTUAL MICROSCOPY

Keywords: Virtual microscopy, 3D display, GPU rendering

3D datasets production capacity in bioimaging has widely evolved in recent years. This trend also results in a growing demand of more suitable display procedures. In this paper, we propose a new virtual microscopy approach aiming at recovering the third dimension, in order to get closer to analogue microscopes. For this purpose, we rely on multi-view autosteroscopic display with off-centered parallel virtual cameras to ensure 3D perception for a more realistic user experience. Also, this approach handles very large volume data size thanks to an out-of-core data management structure which offers interactive navigation by using complete GPU algorithms.

INTRODUCTION

Nowadays, the volume of 3D datasets tends to increase in nearly all application fields. Such an observation is especially true with the current image acquisition technologies used in biology [START_REF] Amunts | BigBrain: An ultrahigh-resolution 3d human brain model[END_REF]. Despite the large amount of generated data, efficient visualization tools are needed to improve three-dimensional structures understanding. Among the possible methods available to overcome this problem, virtual microscope is a tool of choice in the biological field.

A virtual microscope could be defined as a system simulating the observation of microscopic samples on a computer. It aims to mimic a conventional microscope, enabling observation, navigation [START_REF]Deep zoom[END_REF][START_REF]Openseadragon[END_REF], and annotation of virtual slides [START_REF] Corredor | Flexible architecture for streaming and visualization of large virtual microscopy images[END_REF]. The latest virtual microscopy developments [START_REF] Catalyurek | The virtual microscope[END_REF][START_REF] Wang | Vir-tualMicroscopy: Ultra-fast interactive microscopy of gigapixel/terapixel images over internet[END_REF][START_REF] Molin | Scale Stain: Multi-resolution feature enhancement in pathology visualization[END_REF] have addressed the issue of huge data size. However, as of today, another crucial issue has not been considered: users were frustrated by the availability of only one single plain focus, and the induced loss of three dimensional perception [START_REF] Hortsch | From microscopes to virtual reality -How our teaching of histology is changing[END_REF]. To improve the user experience quality and to recover the depth perception, we propose to use autostereoscopic display [START_REF] Holliman | Three-dimensional displays: A review and applications analysis[END_REF] for the 3D visualization [START_REF] Jones | Controlling perceived depth in stereoscopic images[END_REF][START_REF] Lucas | 3D Video: From Capture to Diffusion[END_REF]. To complete the system, we allow the users to freely navigate and zoom in or zoom out in the whole volume rather than in a single slide.

To address this problem, we rely on an out-of-core data management architecture to handle the large volume of data. In most cases, a resolution level pyramid is created where each level is subdivided into data blocks (bricks). Conversely to tree based structures (like Gigavoxels [START_REF] Crassin | Gigavoxels: Ray-guided streaming for efficient and detailed voxel rendering[END_REF]) that can lead to deep tree traversal to access data, we focus our work on the method proposed by Hadwiger et al. [START_REF] Hadwiger | Interactive volume exploration of petascale microscopy data streams using a visualization-driven virtual memory approach[END_REF]. They provide a virtual memory approach with a multi-level, multiresolution page table mechanism. Validated with a concrete application with interactive exploration of petascale volumes by Beyer et al.

This work is supported by the French national funds (PIA2' program) under contract No. P112331-3422142 (3DNS project). We would like to thank the three clusters (Cap Digital and Systematic for ICT and Medicen for Health) that support this project. [START_REF] Beyer | Exploring the connectome: Petascale volume visualization of microscopy data streams[END_REF], this structure offers constant access time between all resolution levels.

Inspired by this out-of-core method, we propose a visualizationdriven approach which generates stereoscopic multi-view frames on GPU in interactive time. The aim is to recover the depth perception in a most realistic way with the use of off-centered parallel virtual cameras focused on a shared point of interest.

A brief overview of the system and data access is provided in section 2. After a detailed description of our virtual microscope approach in section 3), experimental results are presented and discussed in section 4. Finally, section 5 provides concluding remarks and perspective works.

SYSTEM OVERVIEW

The proposed system fully runs on GPUs [START_REF] Sarton | Virtual review of large scale image stack on 3d display[END_REF] and is composed of the virtual microscope and the out-of-core data management. The whole pipeline is called visualization-driven. According to the camera position given by the virtual microscope, data is accessed using the out-of-core data manager. We base our approach on the one proposed by Hadwiger et al. [START_REF] Hadwiger | Interactive volume exploration of petascale microscopy data streams using a visualization-driven virtual memory approach[END_REF]. The data is represented with a multi-resolution bricked pyramid and addressed using a virtualized page table hierarchy. When a chunck of data is missing in the hierarchy, a brick request is raised and handled by the CPU. Bricks are then loaded from its own cache or a mass storage to the GPU. This method allows to get the data on-demand and to address very large volume of data. The whole process is triggered by the virtual microscope depending on the required data.

Data addressing. The voxel access is performed using a virtual volume representation. A pair [l, p] is composed to get through the virtualization hierarchy. The level of detail is determined by l while p ∈ [0, 1) 3 is the 3D normalized coordinate vector of the requested voxel position. Using normalized coordinate vector allows the use of the hardware trilinear interpolation. Finally, the pair [l, p] is sent to the GPU out-of-core memory manager which sends back three possible answers: the requested voxel itself, an empty status if the brick contains no values, or unmapped, warning the system that the brick is not in cache and needs to be fetched.

VIRTUAL MICROSCOPY

The notion of depth perception is usually lost in conventional 2D virtual microscopy. In this work, we provide an approach to recover this perception somehow available with genuine microscopy of thick slices. To achieve this goal, we use multi-view autostereoscopic displays. Such displays rely on N multi-view images shot according to a specific geometry implying off-centered parallel cameras. The number of views N is directly dependent on the display. In our application, the multi-view image generation follows three steps: i) projecting the volume slices on the N views according to the specific multi-camera geometry, ii) applying an alpha blending algorithm in the associated view for each slice projection, and iii) compositing the N views, i.e. creation of the final multi-view image.

The specific geometry implies that N aligned cameras with parallel optical axes and camera line of view converge in a single 3D point (I in Fig. 1). We chose to align the N cameras along the volume x-axis for two reasons: to get volume slices parallel to the sensors and the views, and to get the view lines parallel to the camera baseline, therefore parallel to the volume x-axis. The convergence point I must be displayed at the center of the display. The views are captured in a rectangular region of interest (ROI) of the sensor which is centered on the line of view intersecting each point I i (Fig. 1). This implies that slices are projected on views according to a ROI which is also centered on the camera line of view. Thus, projecting a given volume slice on a view relies on identifying the involved slice ROI projection on the view ROI.

Views generation

The first step of the pipeline begins with the determination of all the parameters required to project the volume slices on the views. In order to meet autostereoscopic multi-view requirements, each virtual camera must aim at a shared point of interest I whose projections are centered in each of the N view (Fig. 1), numbered i ∈ [0, N -1]. I i is I projection (Fig. 2). As shown on figure 2

[Usi, Vsi] = W 2 + βi -αi(x) H 2 + δi -γi(y) (3)
Equations ( 3) express the M si pixel coordinates from Ms space coordinates. Reverting those equations will result in expressing the space coordinates [x, y, zs] in slice s of any pixel of the view i:

[x, y] = Fix -( W 2 + βi -Usi) × d+zs f Fiy -( H 2 + δi -Vsi) × d+zs f (4)
The focal point Fi and [βi, δi] are known and have been calculated previously. The sizes W and H are related to the display definition. Note that zs is the z-axis coordinate of the slice s projected on the view i. Once [x, y] are calculated, their values must be normalized to be used in the addressing structure (see Sec. Multi-camera geometry. A shooting geometry is required to fit the display geometry and to ensure non-distorted 3D perception. This is the reason why off-centered parallel geometry is needed. Moreover, non-distorted 3D perception implies homothetic connection display and camera geometry. The display geometry implies N off-centered (or favorite) user eyes positions Oi lying in front of the screen. They are aligned with the display lines at a distance D from the screen. Those eyes positions are spread by the average human binocular distance (b = 65 mm). The display and camera geometries are compared according to the eyes Oi -centre of display C, and the focal points Fi -convergence point I relative positions. Non-distorted 3D perception requires OiC FiI with i ∈ [0, N ). Knowing the display geometry (Fig. 3): Slice selection. The most important slice is the one containing the point of interest. Consequently, the slice Iz is always projected on the first view. However, the slices projected on the other views need to be determined. In order to recover the depth perception, we use the slice behind Iz. Determining which slice to consider can be done using a parameter ∆z. For a view i, the associated slice will be s = Iz + i × ∆z. The choice of ∆z value is at user's discretion. Nevertheless, the data characteristics need to be studied to select the best value for ∆z (see Sec. 4).

Oi =   (i -N 2

Alpha generation

The alpha generation is performed using a two-step process. First, the pixels of each view are assigned an alpha value. This step can be compared to a standard classification where, for instance, four classes could be used: background, interest tissues, non-interest tissues, and artefacts. The user defines an alpha value for each class, and each pixel will be assigned the apha value corresponding to its closest class alpha value. What is noteworthy is that the choice of the classification algorithm to use will have an impact on the result quality, as well as on the computational time needed to classify all pixels

Once the alpha values are set, an alpha blending process is performed, consisting in applying a back-to-front alpha blending following the painter's algorithm. This process determines the contribution of the back views, according to a certain amount, in the front views. The depth perception is therefore recreated.

Compositing

The compositing is the final step of the pipeline, providing a final multi-view frame F. This frame is generated using the N pre-build views V i , and is composed by using filtering masks M on the views (Fig. 4). These masks are binary filters (M i = {0, 1} 3 [Z 2 ]), and determine, for all views, which color components will contribute to the final frame composition. This step can be expressed as Fc = i V i c M i c where c ∈ {R, G, B}. The filtering masks mechanism is dependent of the display. This process may differ, and take more or less computing time, depending on the used hardware.

RESULTS AND DISCUSSION

The experiments were made using three different datasets: The dataset (a) is the proof of concept of our system (Fig. 5). The dataset (b) demonstrates that our system can be applied to different modalities. Finally, the dataset (c) is used to compare the result with the dataset (a), acknowledging the former has a strongest anisotropy than the latter. The display used was a HD (16:10) autosteroscopic 8-views display with a 1920 × 1200 viewport and requiring a distance -display of 2 m. The same test scenario was applied on the three datasets, and consists of a zoom-in, a pan navigation, then a navigation in the stacks. Multi-view frame generation. The first noticeable fact is the independence between the frame rendering time and the volume data or the acquisition modality. Considering the time allowed to other required processes (out-of-core data management) the method offers a real-time navigation with an average of 30 fps. In the presented test, the rendering pipeline was performed at each frame to simulate the worst case scenario in which this needs to be done every time. Nevertheless, in concrete situation, the whole pipeline should be triggered only when a change is detected in the camera position. The first step recorded is the volume projection on the views only. The average time to generate the views was around 11-12 ms. The dataset (c) took less time to project because of its size, as the volume did not fill entirely the views. In fact, on pixels in the outside borders of the views, we try to project information that is outside the volume. In that case, we are outside the bound of normalized volume sizes and there is no need to continue to process the projection; therefore the frame are generated faster.

• (a) A
The set alpha step consists in computing the Euclidean distance between the voxels and different clusters. In the tests, we used five clusters computed beforehand using a k-means algorithm. The choice in the classification algorithm is of importance: the computation runtime can affect the time to render a view, therefore the navigation fluidity. The difference noticed in the results is related to the data type differences between the volumes. While the dataset (b) uses grayscale pixels, the others use RGBA pixels. Therefore, the pixels assignment is performed faster on (b) than (a) and (c).

Depth perception. As stated in section 3.1, the value ∆z is of importance in the proposed method, as a non optimal value may induce an uncomfortable visualization. During the tests, we noticed that the differences between two slices were small in the dataset (b). The depth perception was recovered by using ∆z = 3. However, this also underlines that visualizing a grayscale works better with highcontrast or color data. An extra step may be required to colorize the data via LUTs. The extreme case happened with the dataset (a). As expected, the volume anisotropy was significant and required to use a ∆z < 1. Depending on ∆z value, the number of slices the user can see in a multi-view frame may be drastically reduced, however the final result is softened. Having ∆ < 1 is possible because we are addressing the data using normalized coordinates. The used outof-core data structure relies on the GPU texture memory and allows trilinear interpolations. However, misusing this value may reduce the depth effect and in turn make the approach irrelevant. Yet, the data anisotropy is an important factor to consider when using this approach.

Camera positioning. In the given approach, the views are positioned on the same plane as the slices. This could be improved using an orbital camera. One could be able to analyse the volumes in a different view angle. However, the data anisotropy would be a major concern and would require a better alternative than simply using a ∆z parameter.

To test our method, an autostereoscopic display was used, where the user has to move in front of the display to move inside the multiview frame. With current technologies, it could be interesting to use the same approach on tablet devices, as it may be more convenient for the user to move the device left and right than to move in front of a screen. Finally, all tests were performed and assessed by the authors. The method is ready for statistical studies with the endusers, using lightsheet or histological datasets and using different parameters.

CONCLUSION

We introduced a proof of concept to virtualize a microscope using off-centered parallel cameras and an autostereoscopic display. With the help of current GPUs, this approach allows the user to interactively navigate through multi-resolution images. This allows data visualization similar to an analogue microscope visualization by recovering the depth perception. Taking advantage of the out-of-core data management, the proposed approach works independently of the data size, from MB to several TB. In addition, the concept offers a similar user experience accross different volume modalities, without significant differences in rendering time. In the future, the development of an approach offering the ability to use an orbital cameras would be of great benefits to this method.

Fig. 1 .

 1 Fig. 1. Representation of the top and side views of the virtual scene and camera geometry. (a) top view, (b) left side view (with the top view as reference). For both views, the volume is represented on the top and the camera focal points Fi and sensors are at the bottom. Off-centered parallel cameras are used with a common point of interest I. I i is the projection of I on the view i given the focal point Fi. The line Fi, I is the line of view i implying I i ∈ (I i I).

  , a view i has a W × H size, implying that the screen space coordinates of I i are always [ H 2 , W 2 ]. Considering that a slice s is projected on a view i, each pixel coordinates of this view are [Usi, Vsi]. Identification of the slice s ROI projected on the view i relies on the geometric

Fig. 2 . 2 )

 22 Fig. 2. Screen space representation. A view is considered as a rectangular ROI in the camera sensor. On this figure, the view has a W × H size (display size), and is centered at I i around the camera line of view. M si is the projection of the point Ms on the view at coordinates [Usi, Vsi] where i refers to the i-th view and s the slice in which Ms lies.

  2). Thanks to GPU threading, and texture handling, equations (4) are used to compute each pixel [Usi, Vsi] ∈ [0, W ) × [0, H) in a dedicated thread by alpha blending (see Sec. 3.2) of its previous value and the 3D interpolation of slice s at [x, y].

Fig. 3 .Fig. 4 .

 34 Fig. 3. User favorite position in front of the display. The Oi are the focal points of the user favorite eyes positions. These points are aligned on the x-axis, shifted by the average binocular distance b (65 mm). The display is positioned at a distance D from the user. x x x + + = filter 0 filter 1 filter 2 image 0 image 1 image 2

Fig. 5 .

 5 Fig. 5. Multi-view frame generated. Example resulting from the histological volume.

  114 histological slices stack of a mouse brain with a resolution of 64000 × 50000 RGBA pixels (1.459 TB); • (b) A 2160 × 2560 × 1072 volume with grayscale 16 bits voxels (11 GB) of a primate hippocampus from a light sheet microscope; • (c) A 645 blockface slices stack of the mouse brain (a) with a resolution of 823 × 202 RGBA pixels (428 MB).

Table 1

 1

				shows the average
	time recorded to generate a complete multi-view frame.
		(a) (b) (c)
	Generate frame 11	12	7
	Set alpha	8	5	8
	Alpha blending	5	5	6
	Compositing	5	5	5
	Sum	29	27	26

Table 1 .

 1 Average rendering time in milliseconds of a frame for three different datasets.