https://bugs.kde.org/show_bug.cgi?id=294594
--- Comment #20 from DrSlony <b...@londonlight.org> --- Gwenview should let the user decide on the compression quality and in the case of JPEG files on the chroma subsampling. 1. Hard-coding any compression level is wrong. 2. Hard-coding any chroma subsampling method is wrong. 3. Forcing images to save using a guesstimate of their original compression quality and chroma-subsampling is wrong. Regarding compression quality. What happens when you open an image saved at compression quality 80, crop it, and save it at compression quality 98? The result looks worse than it did at 80%. 1a. This image was saved from lossless to JPEG using compression quality 80 and 4:2:0 chroma subsampling: https://filebin.net/f6ynfe1acaqtxc68/img_80x1_4_2_0.jpg 1b. This image was saved from lossless to JPEG using compression quality 80 and 4:2:0 chroma subsampling, then the output was used as input and re-saved using quality+1, and so looped all the way up until it reached quality 100: https://filebin.net/f6ynfe1acaqtxc68/img_80-100_4_2_0.jpg 1c. This image was saved from lossless to JPEG using compression quality 80 and 4:2:0 chroma subsampling, then the output was used as input and re-saved using the exact same quality 80, this was done 21 times: https://filebin.net/f6ynfe1acaqtxc68/img_80x20_4_2_0.jpg In order of quality they are 1a, 1c, 1b. Using a low quality is bad enough, but re-saving using a different quality than the original can be worse. Regarding chroma subsampling, again the user should be able to choose. When saving a screenshot as JPG, even a high quality won't help you if you're not using 4:4:4 chroma subsampling, because screenshots typically have 1 pixel-wide lines and their color will be destroyed unless using 4:4:4. Then again, saving a 24 megapixel photo at its full size using 4:4:4 is just a waste of space as your lens is unlikely to be sharp enough to capture pixel-wide detail, however if you downsize this 24 megapixel image to say 900x900, now the situation is different. Now your small photo can have pixel-wide detail, just as a screenshot. Save a downscaled photo of distant street lights or christmas tree lights without using 4:4:4 and you get garbage Assuming that the desired output quality and chroma subsampling should be the same as the input is to misunderstand how the whole thing works. Let the user choose. -- You are receiving this mail because: You are watching all bug changes.
