AWARE SYSTEMS
TIFF and LibTiff Mail List Archive

Thread

2005.06.07 18:43 "[Tiff] Group4 compression & alpha channel", by Bob Friesenhahn
2005.06.07 19:15 "Re: [Tiff] Group4 compression & alpha channel", by Andrey Kiselev
2005.06.07 19:29 "Re: [Tiff] Group4 compression & alpha channel", by Bob Friesenhahn

2005.06.07 19:29 "Re: [Tiff] Group4 compression & alpha channel", by Bob Friesenhahn

It has been observed that when GraphicsMagick writes a min-is-black TIFF image with Group4 compression and an alpha channel (as an extra sample) that the right half of the image is lost. The image description is:

Are there any known issues in libtiff with this scenario?

I do not remember any reports of such a bug. I think it is a matter for our Bugzilla.

Will do once I have spent more time on the issue. Before anyone should mention it, I certainly agree that storing the alpha channel as an extra 1-bit sample does not make much sense for FAX and group4 compression. It makes much more sense to save the alpha channel as a separate plane so it is easier to compress.

Bob
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Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/