On Oct 8, 2006, at 5:21 PM, Jozef Legeny wrote:

PNG supports indexed and grayscale color modes which aren't lossless,
however by default the PNG is entirely lossless

That is a bit of a weird definition of lossless. If you save an RGB32 image as an indexed or grayscale PNG then yes, you've lost information. But that is inherent to grayscale and indexed images. You should have saved that as an RGB32 image, which PNG fully supports. In this case it isn't PNG throwing data away (like JPEG does), but the image editor (GIMP) converting to indexed/grayscale and then saving that. Indexed and grayscale modes in PNG are just as lossless as its non-indexed modes.

However like I said there are methods of tuning the PNG's compression to be lossy, and yet still be PNG-compatible. No image editors that I know of implement these methods, however. (http://membled.com/work/ apps/lossy_png/).

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