JDK-8274735, JPEG compression in a TIFF container, openjdk/jdk/pull/7849

[Brett Okken]

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.babacek at 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
>