randy408
commented
4 years ago Changes made for libpng compatibility so far:
- Handle invalid palette indices as black, opaque pixels - https://github.com/randy408/libspng/commit/4955d6449b8fd62083b924c973461687888857dc
- Ignore tRNS chunks for grayscale alpha / truecolor alpha images - #118
- Do not check the text field of tEXt, zTXt chunks - #123
- Ignore sBIT chunk length for color type 6 (RGBA) - #131
- Discard ancillary chunks with an invalid CRC by default - #138
- Discard chunks with zlib errors by default - #151
This is a meta-issue is for all libpng compatibility issues caused by strict conformance checks.
libspng is very strict with parsing PNG's, almost any deviation from the standard results in an error. This can cause issues because libpng's implementation is the de facto PNG standard which is a lot more loose with checks, it will issue warnings/skip invalid chunks as long as the image can be decoded.
libspng should be able to decode PNG's that aren't standard conformant but are decoded by libpng in most cases, this should be the default behavior with an option to reenable these checks if there is demand for it.