AWARE SYSTEMS
TIFF and LibTiff Mail List Archive

Thread

2003.02.03 18:11 "Pre-multiplied alpha", by Dante Allegria
2003.02.04 04:04 "Re: Pre-multiplied alpha", by Chris Cox
2003.02.04 16:02 "Re: Pre-multiplied alpha", by Dante Allegria
2003.02.04 17:23 "Re: Pre-multiplied alpha", by Daniel McCoy
2003.02.04 22:37 "Re: Pre-multiplied alpha", by Chris Cox
2003.02.05 00:49 "Re: Pre-multiplied alpha", by Chris Cox
2003.02.05 13:29 "Re: Pre-multiplied alpha", by Jan Edmundson

2003.02.04 16:02 "Re: Pre-multiplied alpha", by Dante Allegria

 --- Chris Cox <ccox@adobe.com> wrote: >

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.

Hi Chris,

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.

Thanks.

dante

=====
------------------------------------------------------------

______________________________________________________________________
Post your free ad now! http://personals.yahoo.ca