JPG is a lossy compression format. Each time you decompress and recompress you are doing so likely at different qualities and different algorithms. So naturally you will get different numbers of colors. I don't think there is a good way to do this with IM and use JPEG format. You can use trial and error with -quality to see if you can get nearly the same number of colors, but the colors may not be exactly the same, only similar. IM uses a default -quality of 85, if it has not estimate from the input jpg.
see http://www.imagemagick.org/Usage/formats/#jpg http://www.imagemagick.org/script/command-line-options.php#quality >Hi there, > >I've got a big problem. I'm using convert to store a JPG as JPG and even >if I do not use any parameters, the amount of colors, reported by >Identify, varies. > >Example: >A JPG picture, RGB Colorspace (with 8bit depth per channel), round about >700.000 Colors. After using convert without any parameters, the amount >of colors in the result file is about 1.500.000. > >But what we want, even if JPG probably doesn't support that, is to keep >the amount of colors and the colors itselfs as close to the original >amount respectivly as true, as possible. > >I'd be very lucky if anyone would have a suggestion for me/us. > >Thanks a lot in advance an greetings from >B. Bartels _______________________________________________ Magick-users mailing list [email protected] http://studio.imagemagick.org/mailman/listinfo/magick-users
