On Mon Nov 17 20:39:34 2025 +0000, Esme Povirk wrote:
I guess that's this part of [the spec](https://www.w3.org/Graphics/GIF/spec-gif89a.txt):
ESTABLISH CODE SIZE
The first byte of the Compressed Data stream is a value indicating the minimum number of bits required to represent the set of actual pixel values. Normally this will be the same as the number of color bits. Because of some algorithmic constraints however, black & white images which have one color bit must be indicated as having a code size of 2. This code size value also implies that the compression codes must start out one bit longer. Not sure how we would go about testing this. The initial code size is encoded in the stream, so (unless the decoder assumes this value) the file should decode properly regardless. I wouldn't expect it to be visible through WIC. I think the test would have to parse the image data itself. On the other hand IWICBitmapFrameEncode::SetPixelFormat() sets the format to GUID_WICPixelFormat8bppIndexed, so it's unclear how the LZW compressor would get an image with bpp different from 8.
-- https://gitlab.winehq.org/wine/wine/-/merge_requests/9486#note_122608