2003.02.04 16:02 "Re: Pre-multiplied alpha", by Dante Allegria
Sorry, but nothing changed in that regard.
TIFF specifies that images with transparency (at least one associated alpha channel) must be premultiplied (black for RGB/Grayscale, white for CMYK), and Photoshop has always and will continue to treat it that way until the TIFF specification changes.
Perhaps I misstated what I had meant. I have a test image file that has its colour data pre-multiplied with its alpha already, while also supplying the alpha plane. In the ExtraSamples tag, it is set to a value of 1 (Associated alpha data with pre-multiplied color). For more info, see Section 18 of the TIFF6 standard. In Photoshop 6, it seems to think that this tag is set to 2 and not 1. Attached is a sample tiff demonstrating the problem.