People,
On 2010-01-16 00:11, yahvuu wrote: > Philip Rhoades wrote: >> What still doesn't make sense is that if the original file is JPG and >> one simply opens it and then saves it as another JPG file with 100% >> quality - you are saying that introduced artifacts are adding about 150% >> to the file size? (681 KB to 1.618 MB) How could the compression >> algorithms be so different as to cause this sort of result? - At worst >> I would have expected maybe a 10% increase in size . . > > well firstly, 1.6MB are not that bad in comparison to 9MB of raw RGB data, > right? > (just try saving to uncompressed BMP as Greg suggested). > > Btw, 100% quality for JPG gives very little visible advantage over the > default 90% setting. > > The relationship between quality value, file size and perceived image quality > is very delicate. Any assertion has to be made with a lot of weasel words. > So yes, compression artifacts have a tendency to hinder compression, > resulting in larger file sizes after re-compression to comparable quality. > A similar effect is caused by noise. So to get optimal JPG files, it's > best to use a RAW->XCF->JPG workflow where the JPG is created only once. > > Just have a look at the advanced settings in the JPG save dialog to get > a first impression of what machinery is at work here. There also was a > very long thread on gimp.developer on that very quality setting... > > How does image quality compare if you adjust the quality slider > such that the resulting file size is about 680KB? To my eye, it doesn't look much different - I guess I see the pixellation more quickly when the image is enlarged . . I guess what is confusing is this: - there was a loss of information when the first JPG was saved in the digital camera memory from the CCD - when the JPG is uncompressed by GIMP into RAM, there is no loss of information (?) - when GIMP then saves the same image as a new JPG at 100% quality (I would have thought that this meant not losing any more information), that the second JPG would be compressed/created in much the same way as the first and therefore would be about the same size . . Good to know that this happens anyhow . . of course I have no control over the file format that the camera uses and cropping a camera image and actually getting a result that is 2.5 times the size of the original is a bit annoying . . Thanks, Phil -- Philip Rhoades GPO Box 3411 Sydney NSW 2001 Australia E-mail: p...@pricom.com.au _______________________________________________ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
