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False, or misleading. The AV1 spec [1] does not allow RGB color spaces, therefore AV1 cannot preserve RGB animations in a bit-identical fashion. [1] https://a

False, or misleading. The AV1 spec [1] does not allow RGB color spaces, therefore AV1 cannot preserve RGB animations in a bit-identical fashion. [1] https://aomediacodec.github.io/av1-spec/av1-spec.pdf https://aomediacodec.github.io/av1-spec/av1-spec.pdf

pornel 1y ago
AV1 supports YCoCg, which encodes RGB losslessly. It is a bit-reversible rotation of the RGB cube. It makes the channels look more like luma and chroma that the codec expects.
- meindnoch 1y ago
  False. 8-bit YCoCg (even when using the reversible YCoCg-R [1] scheme) cannot represent 8-bit RGB losslessly. The chroma channels would need 9 bits of precision to losslessly recover the original 8-bit RGB values. [1] https://www.microsoft.com/en-us/research/wp-content/uploads/2016/06/Malvar_Sullivan_YCoCg-R_JVT-I014r3-2.pdf https://www.microsoft.com/en-us/research/wp-content/uploads/...
  - pornel 1y ago
    AVIF supports 10 and 12 bit encoding, which losslessly fits the 9-bit rotation of 8-bit data. It's also possible to directly encode RGB (channels ordered as GBR) when you set identity matrix coefficients, it's just less efficient. I've implemented this in my AVIF encoder, so I know what I'm saying.
    - meindnoch 1y ago
      Show me any of the popular image conversion tools (avifenc, imagemagick, photoshop, ffmpeg, whatever...) that does the identity matrix hack when asking for lossless AVIF. None of them do it. Many people have been burned by "lossless" AVIF, where they converted their images in the mistaken belief that the result will be bit-identical to the original, only to find out that this wasn't the case, after they've deleted the original files.
      - fc417fc802 1y ago
        That's shifting the goalposts from what the standard supports to the current state of the ecosystem. It's certainly an interesting point though. If common implementations all have bugs regarding lossless encoding that's a pretty bad situation.

pornel 1y ago

AV1 supports YCoCg, which encodes RGB losslessly. It is a bit-reversible rotation of the RGB cube. It makes the channels look more like luma and chroma that the codec expects.

meindnoch 1y ago
False. 8-bit YCoCg (even when using the reversible YCoCg-R [1] scheme) cannot represent 8-bit RGB losslessly. The chroma channels would need 9 bits of precision to losslessly recover the original 8-bit RGB values. [1] https://www.microsoft.com/en-us/research/wp-content/uploads/2016/06/Malvar_Sullivan_YCoCg-R_JVT-I014r3-2.pdf https://www.microsoft.com/en-us/research/wp-content/uploads/...
- pornel 1y ago
  AVIF supports 10 and 12 bit encoding, which losslessly fits the 9-bit rotation of 8-bit data. It's also possible to directly encode RGB (channels ordered as GBR) when you set identity matrix coefficients, it's just less efficient. I've implemented this in my AVIF encoder, so I know what I'm saying.
  - meindnoch 1y ago
    Show me any of the popular image conversion tools (avifenc, imagemagick, photoshop, ffmpeg, whatever...) that does the identity matrix hack when asking for lossless AVIF. None of them do it. Many people have been burned by "lossless" AVIF, where they converted their images in the mistaken belief that the result will be bit-identical to the original, only to find out that this wasn't the case, after they've deleted the original files.
    - fc417fc802 1y ago
      That's shifting the goalposts from what the standard supports to the current state of the ecosystem. It's certainly an interesting point though. If common implementations all have bugs regarding lossless encoding that's a pretty bad situation.