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10.4: Add Spotlight keywords to images with Preview
Authored by: network23 on Jun 17, '05 12:08:01PM

Something is definitely going on with the image when you add the keywords via Preview, but from what I can tell, the image is not being recompressed. I took a file, copied it, and added keywords to the copy multiple times, resulting in six additional saves. I then loaded them up in Photoshop and looked at them at 1600%. No pixels shifted or looked recompressed (the "layout" of pixels from the original compression looked identical), but I did notice some slight color shifting in some of the pixels. At 1200-1600%, the copied image looked more "rainbow-y" than the original, but when viewed at normal size, little, if any, change could be discerned.

So the image is being altered, but I do not think it is being recompressed.

I've posted my test image comparison.

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10.4: Add Spotlight keywords to images with Preview
Authored by: SeanAhern on Oct 07, '05 02:17:10PM

I think it's likely that it's being recompressed. Recall that JPEG compression involves color manipulation so as to remove colors that the eye "cannot see".

I took your two images that were side by side, brought them into Photoshop, and differenced them. The resultant image was almost black, but not quite. Once I adjusted the contrast to highlight the differences, you can easily see a variation. See here.

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