RSS/Atom feed Twitter
Site is read-only, email is disabled

JPEG encoding question

This discussion is connected to the gimp-developer-list.gnome.org mailing list which is provided by the GIMP developers and not related to gimpusers.com.

This is a read-only list on gimpusers.com so this discussion thread is read-only, too.

3 of 3 messages available
Toggle history

Please log in to manage your subscriptions.

JPEG encoding question Michael Cherkasov 03 Jun 17:41
  JPEG encoding question Nicolas Robidoux 03 Jun 20:06
   JPEG encoding question Michael Cherkasov 03 Jun 22:50
Michael Cherkasov
2014-06-03 17:41:41 UTC (almost 10 years ago)

JPEG encoding question

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.

Nicolas Robidoux
2014-06-03 20:06:59 UTC (almost 10 years ago)

JPEG encoding question

Nothing to do with GIMP: JPEG does not support transparency. Search for "jpeg transparency". You'll get links like: http://corner.squareup.com/2013/01/transparent-jpegs.html.

Michael Cherkasov
2014-06-03 22:50:44 UTC (almost 10 years ago)

JPEG encoding question

Hi Nicolas,
thank you for answer.
But GIMP opens this file, so the question is how it treats 4 channels? why it shows this color not other?

Thanks, Michael.

2014-06-04 0:06 GMT+04:00 Nicolas Robidoux :

Nothing to do with GIMP: JPEG does not support transparency. Search for "jpeg transparency". You'll get links like: http://corner.squareup.com/2013/01/transparent-jpegs.html.