36-Issue 7

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https://diglib.eg.org/handle/10.2312/2631805

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Browsing 36-Issue 7 by Subject "Display algorithms"

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    Efficient Gradient-Domain Compositing Using an Approximate Curl-free Wavelet Projection
    (The Eurographics Association and John Wiley & Sons Ltd., 2016) Ren, Xiaohua; Luan, Lyu; He, Xiaowei; Zhang, Yanci; Wu, Enhua; Jernej Barbic and Wen-Chieh Lin and Olga Sorkine-Hornung
    Gradient-domain compositing has been widely used to create a seamless composite with gradient close to a composite gradient field generated from one or more registered images. The key to this problem is to solve a Poisson equation, whose unknown variables can reach the size of the composite if no region of interest is drawn explicitly, thus making both the time and memory cost expensive in processing multi-megapixel images. In this paper, we propose an approximate projection method based on biorthogonal Multiresolution Analyses (MRA) to solve the Poisson equation. Unlike previous Poisson equation solvers which try to converge to the accurate solution with iterative algorithms, we use biorthogonal compactly supported curl-free wavelets as the fundamental bases to approximately project the composite gradient field onto a curl-free vector space. Then, the composite can be efficiently recovered by applying a fast inverse wavelet transform. Considering an n-pixel composite, our method only requires 2n of memory for all vector fields and is more efficient than state-of-the-art methods while achieving almost identical results. Specifically, experiments show that our method gains a 5x speedup over the streaming multigrid in certain cases.
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    Photometric Stabilization for Fast-forward Videos
    (The Eurographics Association and John Wiley & Sons Ltd., 2016) Zhang, Xuaner; Lee, Joon-Young; Sunkavalli, Kalyan; Wang, Zhaowen; Jernej Barbic and Wen-Chieh Lin and Olga Sorkine-Hornung
    Videos captured by consumer cameras often exhibit temporal variations in color and tone that are caused by camera autoadjustments like white-balance and exposure. When such videos are sub-sampled to play fast-forward, as in the increasingly popular forms of timelapse and hyperlapse videos, these temporal variations are exacerbated and appear as visually disturbing high frequency flickering. Previous techniques to photometrically stabilize videos typically rely on computing dense correspondences between video frames, and use these correspondences to remove all color changes in the video sequences. However, this approach is limited in fast-forward videos that often have large content changes and also might exhibit changes in scene illumination that should be preserved. In this work, we propose a novel photometric stabilization algorithm for fast-forward videos that is robust to large content-variation across frames. We compute pairwise color and tone transformations between neighboring frames and smooth these pair-wise transformations while taking in account the possibility of scene/content variations. This allows us to eliminate high-frequency fluctuations, while still adapting to real variations in scene characteristics. We evaluate our technique on a new dataset consisting of controlled synthetic and real videos, and demonstrate that our techniques outperforms the state-of-the-art.