About the methodology of using identical colorspace conversion for all formats, the study asserts > and manual visual spot checking did not suggest the conversion > had a large effect on perceptual quality
I think this claim should be examined more carefully. Take this image, for example: https://i.imgur.com/3pgvjFl.png WebP quality 100, decoded to PNG: https://i.imgur.com/O6KKOZy.png JPEG q99, 4:2:0 subsampling: https://i.imgur.com/jqdMv0d.jpg WebP (in lossy mode) can't code it without visible banding. Even if you set the quality to 100, the 256 -> 220 range crush destroys enough information that even if nothing was lost in the later stages it'd still show significant problems. How visible this is depends on the particular screen or viewing environment. I notice it immediately on the three devices I have at hand, but I guess on some screens it might not be so obvious. Here are the same 3 files with their contrast enhanced for easy differentiation: Original: https://i.imgur.com/zXQ4Z5D.png WebP: https://i.imgur.com/NBm9abp.png JPEG: https://i.imgur.com/ASU94A7.png Then there's the issue of only supporting 4:2:0, which is terrible for synthetic images (screen captures, renders, diagrams) and shows in natural images too. 4:4:4 subsampling is used a lot in practice, for example Photoshop uses it automatically for the upper half of its quality scale when saving JPEGs. At high qualities it's often better to turn chroma subsampling off even at the expense of slightly higher quantization. I suspect these two issues are the reason WebP hits a quality wall in some JPEG/JXR/J2K comparisons done in RGB space. _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
