New answers tagged image-compression
I did some more tests and I think the issue is color space conversion. Here's the testing procedure I used with Photoshop CC 2014: Create a new file with 8-bit, Adobe RGB 1998 color space. Create a rainbow gradient. Save for Web as PNG; don't convert to sRGB. Place embedded the PNG file just saved. Change PNG layer blend mode to difference. There is a very ...
PNGs can be compressed either using either lossless or lossy compression.
If a jpeg has been resaved as another jpeg, the file size will always change because the image will undergo lossy compression. I.e. when you lose some information, the size of the file will change because the image is now a tiny bit different. Did you apply any curves or levels to the image difference to exaggerate the difference between the two images?
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