* Anne Wilson <[EMAIL PROTECTED]> [030224 07:00]: > I thought that png was a lossless compression - am I wrong?
No, you are right. > If I start from a jpg file from my camera, 397 KB, why does saving it as a png > come out at 2.4MB? Because .png IS a lossless compression. Your camera is using a lossy format, .jpg, to reduce your images to 397 KB. If you then save it as a .png, you are saving the already lossy image in a lossless format, resulting in a much larger file. The .png you make does not contain any additional information than what was in the original .jpg, so it is questionable how useful that is. So why use .png at all? Well, I use it a lot for screenshots for training. One thing .jpg does NOT do well is represent typical application program screenshots. Areas that should appear all the same color often have "artifacts" (distortions) when saved in .jpg format. Actually, photos do too, but usually they are less obvious. Another good use for a lossless compression like .png is when you will be using a photo editor to edit the file. If you edit a .jpg, you take an already lossy image, edit it ... all photo editors I know use a lossless compression technique internally, at least while they are editing the image ... and then save it. If you save it as a .jpg, the image is compressed in a lossy manner, and these losses can accumulate. The GIMP's native format, .xcf, is lossless, and can get HUGE, but that's the expense of using lossless but better quality compression. -- Jan Wilson, SysAdmin _/*]; [EMAIL PROTECTED] Corozal Junior College | |:' corozal.com corozal.bz Corozal Town, Belize | /' chetumal.com & linux.bz Reg. Linux user #151611 |_/ Network, PHP, Perl, HTML
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