Browsing by Author "Barla, Pascal"

Now showing 1 - 5 of 5
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    Comparative Study of Layered Material Models
    (The Eurographics Association, 2019) Bati, Mégane; Pacanowski, Romain; Barla, Pascal; Klein, Reinhard and Rushmeier, Holly
    The accurate reproduction of layered materials is an important part of physically-based rendering applications. Since no exact analytical model exists for any configuration of layer stacks, available models make approximations. In this paper, we propose to evaluate them with a numerical approach: we simulate BRDFs and BTDFs for layered materials in order to compare existing models against a common reference. We show that: (1) no single model always outperforms the others and (2) significant differences remain between simulated and modeled materials. We analyse the reasons for these discrepancies and introduce immediate corrections.
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    Efficient Interpolation of Rough Line Drawings
    (The Eurographics Association and John Wiley & Sons Ltd., 2023) Chen, Jiazhou; Zhu, Xinding; Even, Melvin; Basset, Jean; Bénard, Pierre; Barla, Pascal; Chaine, Raphaëlle; Deng, Zhigang; Kim, Min H.
    In traditional 2D animation, sketches drawn at distant keyframes are used to design motion, yet it would be far too laborintensive to draw all the inbetween frames to fully visualize that motion. We propose a novel efficient interpolation algorithm that generates these intermediate frames in the artist's drawing style. Starting from a set of registered rough vector drawings, we first generate a large number of candidate strokes during a pre-process, and then, at each intermediate frame, we select the subset of those that appropriately conveys the underlying interpolated motion, interpolates the stroke distributions of the key drawings, and introduces a minimum amount of temporal artifacts. In addition, we propose quantitative error metrics to objectively evaluate different stroke selection strategies. We demonstrate the potential of our method on various animations and drawing styles, and show its superiority over competing raster- and vector-based methods.
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    Non-linear Rough 2D Animation using Transient Embeddings
    (The Eurographics Association and John Wiley & Sons Ltd., 2023) Even, Melvin; Bénard, Pierre; Barla, Pascal; Myszkowski, Karol; Niessner, Matthias
    Traditional 2D animation requires time and dedication since tens of thousands of frames need to be drawn by hand for a typical production. Many computer-assisted methods have been proposed to automatize the generation of inbetween frames from a set of clean line drawings, but they are all limited by a rigid workflow and a lack of artistic controls, which is in the most part due to the one-to-one stroke matching and interpolation problems they attempt to solve. In this work, we take a novel view on those problems by focusing on an earlier phase of the animation process that uses rough drawings (i.e., sketches). Our key idea is to recast the matching and interpolation problems so that they apply to transient embeddings, which are groups of strokes that only exist for a few keyframes. A transient embedding carries strokes between keyframes both forward and backward in time through a sequence of transformed lattices. Forward and backward strokes are then cross-faded using their thickness to yield rough inbetweens. With our approach, complex topological changes may be introduced while preserving visual motion continuity. As demonstrated on state-of-the-art 2D animation exercises, our system provides unprecedented artistic control through the non-linear exploration of movements and dynamics in real-time.
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    One-to-Many Spectral Upsampling of Reflectances and Transmittances
    (The Eurographics Association and John Wiley & Sons Ltd., 2023) Belcour, Laurent; Barla, Pascal; Guennebaud, Gaël; Ritschel, Tobias; Weidlich, Andrea
    Spectral rendering is essential for the production of physically-plausible synthetic images, but requires to introduce several changes in the content generation pipeline. In particular, the authoring of spectral material properties (e.g., albedo maps, indices of refraction, transmittance coefficients) raises new problems. While a large panel of computer graphics methods exists to upsample a RGB color to a spectrum, they all provide a one-to-one mapping. This limits the ability to control interesting color changes such as the Usambara effect or metameric spectra. In this work, we introduce a one-to-many mapping in which we show how we can explore the set of all spectra reproducing a given input color. We apply this method to different colour changing effects such as vathochromism - the change of color with depth, and metamerism.
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    Stroke Synthesis for Inbetweening of Rough Line Animations
    (The Eurographics Association, 2020) Chen, Jiazhou; Zhu, Xinding; Bénard, Pierre; Barla, Pascal; Lee, Sung-hee and Zollmann, Stefanie and Okabe, Makoto and Wuensche, Burkhard
    In this paper, we present a stroke synthesis approach for the inbetweening of rough line animations. In pre-process, keyframe strokes are transformed by local perturbation and sliding to generate a number of candidate strokes, and adjacent keyframes are registered together. During inbetweening, candidate strokes are transferred to the intermediate frames and selected based on the desired spatial distribution and length constraints.