Re: [gimp-devel] Re: JPEG correction (was Re: Gimp Wishes)
On Sat, Apr 08, 2000 at 01:24:53AM +0300, Tor Lillqvist <[EMAIL PROTECTED]> wrote: > I have no idea what would be a good way to implement this, or how the > user interface could look. Probably one would need to keep a bitmap of > dirty pixel blocks (or whetever they are called), and when saving, if I'd say for such a really jpeg-only thing, the best way would be to enhance the jpeg save mechanism to first parse the existing file. Seems doable as well. > the more important a pixel block is. Hmm, is this doable in the JPEG > format at all? Yes. But I doubt it would be "legal" (that is, even if legal I doubt decoders would survive reading it ;) > Of course, one could achieve something similar by > simply blurring the unimportant parts before saving. Probably with some kind of "jpeg-blur" that aims at reducing frequency components suited for jpeg... -- -==- | ==-- _ | ---==---(_)__ __ __ Marc Lehmann +-- --==---/ / _ \/ // /\ \/ / [EMAIL PROTECTED] |e| -=/_/_//_/\_,_/ /_/\_\ XX11-RIPE --+ The choice of a GNU generation | |
Re: [gimp-devel] Re: JPEG correction (was Re: Gimp Wishes)
I think it would be a very useful feature to be able to open a JPEG in the GIMP, do some editing that touches just a small minority of the pixels like correcting red-eyes, and save just the edited parts, keeping the rest of the JPEG unchanged. (Not talking about individual pixels, of course, but those 8x8 (?) pixel blocks.) I have no idea what would be a good way to implement this, or how the user interface could look. Probably one would need to keep a bitmap of dirty pixel blocks (or whetever they are called), and when saving, if only a reasonably small minority of the pixel blocks are dirty, the plug-in could offer the user to keep the untouched pixel blocks intact and save just the changed ones. There is a patch to jpegtran that enables it do to lossless cropping. The same patch also enable you to "insert" a smaller jpeg in a larger one without loss. See http://www.reporter.de/digifoto/jpegcrop/ . Another possibly useful JPEG feature would be to be able to use variable quality when saving an image as a JPEG. For instance the selection mask could be used to indicate the relative importance of various parts of an image, and the plug-in would use higher quality the more important a pixel block is. Hmm, is this doable in the JPEG format at all? Of course, one could achieve something similar by simply blurring the unimportant parts before saving. --tml
Re: [gimp-devel] Re: JPEG correction (was Re: Gimp Wishes)
Jon Winters ([EMAIL PROTECTED]) wrote: > The only manipulation I can think of that would benefit from "lossless" > jpeg would be rotating the image. (if I were shooting low-rez) I > remember seeing some tools at the JPEG F.A.Q. site that would rotate a > JPEG without damage. http://www.faqs.org/faqs/jpeg-faq/ This lossless operations depend heavily on knowledge about JPEG internals. They operate without de- and recompressing the image data. You can use them with tools like jpegtran . However, this is nothing to embed into Gimp. Gimp has a totally different approach on storing image data and it is virtually impossible to preserve the JPEG-internal data (parasites for all JPEG-Coefficients - Urgh... ;-) Bye, Simon -- [EMAIL PROTECTED] http://www.home.unix-ag.org/simon/
