From: Greg R. <ne...@po...> - 2008-05-15 16:54:32
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Thomas Kopp wrote: > Technical note concerning the "reference image": > Existing alpha channel values should have to be processed for > transforming the image to an RGB representation (cf. 13.16 in the PNG > specification). The alpha channel should be processed with respect to a > bKGD chunk using color #999999 if none is available (cf. section 13.15). I'm not following--why does it matter how one might transform it to RGB? A PNG image with any amount of transparency (or even with a fully opaque alpha channel) has an RGBA reference image of the corresponding sample depth, and that's what would be signed. Also, sections 13.15 and 13.16 are about chunk types and pixel dimensions, respectively. I don't see anything about reference images or bKGD in there. http://www.libpng.org/pub/png/spec/iso/index-object.html#13Chunking Greg |