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Jpeg encoder writes zeroed chrominance quantization table for grayscale images and RGB encoding #1713
Description
Activity
One little nuance: it can break existing quality estimation if grayscale image have zeroed chroma table and you put some random values or simply a single
1in the DQT binary for chroma table. While image with such 'corrupted' binary is technically correct - it's grayscale and parser shouldn't even care about chroma quant table even if exists. Current implementation does care and thus destroys quality at re-encoding. Not a very usual thing to encounter in real life and it'll be fixed as part of #1705 anyway.Edit: fixed.
- changed the title
[-]Jpeg encoder writes zeroed chrominance quantization table for grayscale images[/-][+]Jpeg encoder writes zeroed chrominance quantization table for grayscale images and RGB encoding[/+]on Sep 18, 2021 Fixed via #2120
Prerequisites
DEBUGandRELEASEmodeDescription
Current implementation of the
JpegEncoderCorewritesBlock8x8F chroma = default(i.e. zeroed) table to the DQT marker for grayscale images. While ITU spec doesn't forbid it - encoder writes proper marker length so everything works fine but it would be extra nice if there's no01+ x6400bytes in the binary.This is super unimportant so it can be marked as 'Future' without a doubt.