提出一种支持4:2:0格式的无损屏幕内容编码方法，提升压缩效率。
Lossless 4:2:0 Screen Content Coding Using Luma-Guided Soft Context Formation
- 基于亮度图指导色度上下文生成，分步编码亮度和色度平面。
- 在大型屏幕图像数据集上，比特率比HEVC-SCC低5.66%。
- 适合需要高效无损压缩屏幕内容的应用场景。
软上下文生成编码器是一种像素级的先进无损屏幕内容编码方法，结合模式匹配、颜色调色板编码与算术编码，在RGB 4:4:4格式且颜色种类少的图像上表现优异。该方法一次性编码一个像素的所有颜色分量，不原生支持色度下采样的格式如YCbCr 4:2:0。本文通过分析图像平面间的归一化互信息，依次编码亮度（Y）和色度（CbCr）平面，并提出基于亮度平面的色度预测改进方案。此外，引入关于亮度-色度组合出现情况的辅助信息，以优化色度概率建模。在大规模屏幕内容图像数据集上的平均测试结果表明，本方法比特率比HEVC-SCC低5.66%。
原文摘要 · Abstract (English)
The soft context formation coder is a pixel-wise state-of-the-art lossless screen content coder using pattern matching and color palette coding in combination with arithmetic coding. It achieves excellent compression performance on screen content images in RGB 4:4:4 format with few distinct colors. In contrast to many other lossless compression methods, it codes entire color pixels at once, i.e., all color components of one pixel are coded together. Consequently, it does not natively support image formats with downsampled chroma, such as YCbCr 4:2:0, which is an often used chroma format in video compression. In this paper, we extend the soft context formation coding capabilities to 4:2:0 image compression, by successively coding Y and CbCr planes based on an analysis of normalized mutual information between image planes. Additionally, we propose an enhancement to the chroma prediction based on the luminance plane. Furthermore, we propose to transmit side-information about occurring luma-chroma combinations to improve chroma probability distribution modelling. Averaged over a large screen content image dataset, our proposed method outperforms HEVC-SCC, with HEVC-SCC needing 5.66% more bitrate compared to our method.
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