JPEG support for RGB with transparency/alpha channel is pretty spotty. https://stackoverflow.com/a/57626892/676877
On Fri, May 20, 2022 at 8:12 AM Michal Karm <michal.baba...@gmail.com> wrote: > I stepped the flow in a debugger and I narrowed > down the reproducer to a more focused, simpler > description and test data: > > https://github.com/Karm/dev-null/blob/main/jpegtiff/README.md > > TL;DR: > > JPEG compressed RGB image in TIFF with transparency makes > the TIFF decoder to push 4 components data to the JPEG reader. > > The JPEG reader wrongly guesses that the data is CMYK now (based on the > number > of components). > > If the image is GRAYSCALE though, it ends up in Unsupported Image Type > because JPEG reader doesn't try to guess it's CMYK. > > > Solution...I don't know. > > Would it make sense if I transform the data to the number of > components the JPEG reader expects? > All the necessary information is there in the TIFF metadata, > e.g. it knows the space is RGB and not CMYK, it knows that there > is a transparency saved with the tile. > > THX for hints > > Karm > > > On 5/17/22 21:52, Philip Race wrote: > > This could be a bug in the TIFF plugin. > > Hard to say without debugging it. > > > > -phil. > > > > > > On 5/17/22 7:04 AM, Michal Karm wrote: > >> Hello, > >> > >> There used to be an Unsupported Image Type exception thrown > >> when one wanted to decode a TIFF container with JPEG compressed image. > >> > >> That behavior has changed, there is no exception now, although the > >> resulting image is incorrect. > >> > >> I outlined the details in this doc [1], including a small reproducer. > >> > >> The test image is not anything from a fuzzer, it's just me > >> clicking Export As in GIMP. > >> > >> Thanks for feedback > >> > >> Cheers > >> Karm > >> > >> > >> [1] > >> > https://urldefense.com/v3/__https://github.com/Karm/dev-null/blob/main/jpegtiff/README.md__;!!ACWV5N9M2RV99hQ!Kw41ShsuTSfpVPMZFrXmdQ7ZETNdkLTk9Xd1NDWELvCXV0fyIqg4sXi5Z1aYfjMoG-5fS0gki8dnN8bQjSYM0g$ > >> > >> > >> Karm Michal Babacek > >> > > > > > Michal Karm Babacek > > -- > Sent from my Hosaka Ono-Sendai Cyberspace 7 >
