View Full Version : PNG files re compress?
Wondered when you open a png in Photoshop CS 1, and alter it then save it, does the png file get re-compressed further, each time you change and save it or does it remain the same?
09-13-2006, 12:01 AM
It shouldn't. And if it does there's something wrong, because it saves by the file's width/height/detail etc.
So it should remain the same.
That's good news thanks...
It would be nice if it did, but no :)
PNG is a lossless algorithm; its compression does not affect the image's quality.
09-13-2006, 09:08 AM
Actually, there can be some truth in "recompressing", as newer algorithms (never versions of libbz2) have improved strenght due being more optimised- you can get PNG recompressed to lesser filesize with newer software (but of coure there's sometimes an absolute limit- usually 92-94 bytes in my test cases for files that had more than one pixel)
pngcrush (http://www.google.com/search?q=pngcrush&btnI=true) is always worth looking into. It doesn't have much of an effect on GIMP-created PNGs (I guess they're already optimised to the limit), but I hear it has quite an effect on Photoshop-engineered ones.
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