2004.01.21 12:10 "Re: [Tiff] Alpha channel worries", by Andrey Kiselev
I have observed some weird effects when trying to save images with alpha channel and loading them later. The loading routine of the OpenBeOS TIFFTranslator just uses TIFFReadRGBAImage(). Images previously saved with that same translator, seem to have been modified to have the color channels associated with the alpha channel. This happens although I specify EXTRASAMPLE_UNASSALPHA for the alpha channel when saving. Is TIFFReadRGBAImage() specifically converting the RGB channels to be associated with the alpha channel (because libtiff assumes that's what the application wants)?
If alpha channel specified in the input image then it will be used by the TIFFReadRGBAImage, because that function intended for displaying purposes only. If you want more control of your data you should avoid TIFFReadRGBAImage interface.
Andrey V. Kiselev
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