Re:PNG and Hidden Pixels
by yodelshady on Tuesday September 01, 2020 @08:07AM
(#24340880)
If it's compressed (it is!) how would you know? You can't simply do width x height x depth.
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PNG's IDAT chunk, which contains actual image data, is simply all lines of data compressed with the deflate algorithm. Once you inflate (uncompress) it, you have all data and can compare if width and height match. This way it is quite easy to detect if additional data was added.