4 ms·
From what I can tell, for Y-SSIM and IW-SSIM they appear to be encoding color images but only measuring the luma component, which is invalid and renders the res
by brigade 13y ago
From what I can tell, for Y-SSIM and IW-SSIM they appear to be encoding color images but only measuring the luma component, which is invalid and renders the results meaningless. Unless they're actually encoding greyscale images for those sections without mentioning it?
BTW HEVC-MSP is limited to 4:2:0 only as well.
- joshmoz 13y agoStudy author here. For Y-SSIM and IW-SSIM we convert the images to grayscale (MATLAB 'rgb2gray') before running the scoring algorithms. We aren't running the algorithms on luma planes. See published code and methodology.
- brigade 13y agoHow are you measuring filesize? Looking at compression_test.py, it looks like you encode a color image and use that filesize. But chroma takes bits to encode, and if you're only measuring greyscale (which is basically luma depending on what formula rgb2gray uses) then you're penalizing better chroma quality. If you use a greyscale/luma-only metric, you have to encode greyscale from the start, not convert a color image after encoding. Otherwise you're measuring chroma bit cost, but not chroma distortion. Thus, invalid. Actually, is PSNR-HVS-M greyscale-only as well? In that case, only the RGB-SSIM results would be valid... And actually, thinking about it even more, converting to greyscale at the tail end just for Y-SSIM and IW-SSIM is fundamentally flawed (if it doesn't result in exactly the same bits as the luma plane), as now you're measuring distortion from an image that the codec was never asked to encode!