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
