>On Mon, Feb 02, 2009 at 01:37:24PM +0100, Claus Cyrny wrote: >> >> I have to admit that, after following this thread, I still >> have no idea what Zhang Wei Wu means by 'lossless 'cropping'. >> I understand' lossless compression', but cropping is by definition >> lossy (you remove part of the original image), so I don't >> know what 'lossless' means in this context. > >I'm going to take a wild guess on this (not having read the rest of >the thread). If you were to take a lossy format (say, mp3 or jpeg), >and cut out portions of the data and then recompresses the remaining >data, the data that remains gets refiltered and suffers more loss >than that just due to the data cropped out. On the other hand, both >mp3 and jpeg support something that could be termed lossless cropping >as long as you cut on the data boundaries (packet in mp3, 8x8 block on >jpeg) where the data you crop out obviously gets thrown out, but the >remaining data does not get refiltered with its resulting additional >informational loss. > >Jeff > >
Yes, that's it. When people talk about lossless jpeg modifications, in 99% they are referring to "elimination of cumulative losses introduced by repeated compression and decompression". (And the other 1% ... there is a kind of JPG-based format that is lossless, but there is almost not support for it in common applications and it has poor compression ratio and hence negates the advantage of classic JPG). -- Vlasta _______________________________________________ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
