11/10/2023 0 Comments Imagemagic jp compression![]() ![]() So if I understand this correctly (which I freely admit I may not), this would have the greatest effect on small files, where for example one ~100 KB file could include several tens of KB of metadata while another might have almost none. In the "Ordered Graph" near the end of the article this is shown clearly, particularly near the low end of the scale where luminance quality begins to fall off sharply beginning around the 20 setting, about the same as in canetti2's screenshot. Even so, neither scale is a percent indicator because they are not linear. the 1-12 one for Save As, so if I had been reading more carefully I would not have been confused by that. According to the Photoshop Save As vs Save For Web article, Save for Web automatically removes EXIF metadata & optional JPEG "markers," described as "special markers used to indicate additional information or provide resiliency in the case of errors / corruption." That same article also mentions the 1-100 quality scale for Save for Web vs. This is why I was asking if the CS2 export was done using the "Save for Web" interface or the "Save as" one. That is because since metadata contributes to file size but not image quality, if one file includes significantly more metadata that another of similar file size, it must have compressed the image with a lower effective quality setting to allow for the metadata 'overhead.' One of the articles I mentioned earlier cautions that this kind of comparison can be deceptive unless both files contain the same kind & amount of metadata. I'm so used to using the mozjpeg command line together with ImageMagick that the quality of built-in jpeg export is non-issue for me, but clearly for a lot of people this can be a make-or-break it kinda situation.Īpparently, it is not quite that simple. Otherwise a resampler would really be a silly option for exporting to tiff or exr :). So the option shouldn't be there in that case.īut I believe it's there to do on-the-fly scaling if you wish, and to round-to-nearest-pixel if you got fractions in your dimensions. Although this would be weird as 'too sharp' for chroma downsampling really gives artifacts, and lanczos (both options) is really not the best for chroma downsampling as I read it. It could also be the case if for a format (like jpeg) it's possible to do chroma subsampling, and the resampler is used to downsample the chroma. And if you export, those boundaries need to be rounded to the nearest full pixel, thus you get a fractional resize (and thus the option to choose your resampler). Isn't it also the case that you can have documents scaled to (for example) 4523.8 by 793.3 pixels in Affinity. If the 100kb is clearly better looking then there is quality difference :P.Ībout the resample options in the export dialog (they are there for all filetypes, not just jpeg): Like the OP, he tweaked the values so that they both give or take got the same filesizes (104kb and 100kb apparently). The results posted by canetti2 show that for an approximate file size of 100Kb the visual quality of the image exported by Photoshop is still superior to the one exported by Affinity no matter the mismatch between the scales (except for Save for Web where both go up to 100) assuming both are using the same settings.Ĭomparisons need to be done at (roughly) the same filesize. With the same image data Photoshop will eventually get a superior result again due to a better export/compression engine. The pre-optimisations you are suggesting are not important because for a fair comparison you have to perform them to the same image on both programs which leads to similar image data before exporting. If you are not resizing the images there's no differences in the results no matter the resample method you pick When you are simply exporting an image without resizing the resampling method is irrelevant (assuming you are not working with a composition where layers where scaled down). They are there because you may want to resize the image and in that case the Resample algorithm does matter. Depending on the document's contents the differences may be small but they are not zero. ![]() Then why are there resample options in the JPEG export dialogs? I did some experimentation exporting at a constant original image size & extreme compression (Quality =10) using Nearest Neighbor & Lanczos settings. ![]()
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