[Gimp-developer] JPEG encoding question

[Michael Cherkasov <michael cherkasov gmail com>]

Hi all,

the jpeg spec http://www.w3.org/Graphics/JPEG/itu-t81.pdf said that
colour space designation is not specified and it's application specific.

So I have a problem with decoding of attached image,
the image has 4 channels, I need to save the alpha channel too.
So the attached image uses YCbCr plus alpha channel.

But if you open image you will see... I don't know how to describe the
color, but originally it was red color 255,0,0 in RGB.

Can you advise how to fix encoding, is it possible to provide a hints to
gimp that image uses YCbCr with Alpha?

And could you clarify how gimp treat 4 channels image? because it doesn't
just
ignore 4th channel, why it choose that color not other?

Thanks,
Michael.