2006.09.26 04:55 "Re: [Tiff] Tiffcrop beta available for testing", by Bob Friesenhahn

Your program sounds pretty neat.

On Mon, 25 Sep 2006, Richard Nolde wrote:

palette, 8 bit RGB, 8 bit RGBA images successfully. The only image that I can't seem to handle is an 8 bit YCbCr with 3 samples per pixel from the libtiff test pics set, dscf0013.tif.

Does anyone have any information on how YCbCr images are handled by the read[Separate/Contig][Strips/Tiles]IntoBuffer routines in tiffcp that would be different for YCbCr data rather than RGBA data?

I don't know the details as pertain to TIFF, but YCbCr is often subsampled, which could mean (e.g. for 4:2:2) there are two Y samples for every pair of CbCr samples. For example Cb,Y,Cr,Y,Cb,Y,Cr,Y so each pixel position is represented by two samples rather than three and at least two pixel positions need to be decoded in order to know (approximately) the color of a pixel.

There are many forms of YCbCr subsampling and each one uses different rules for how the image is represented.

There is a utility program in the libtiff source tree for creating many variants of YCbCr TIFF files. I don't know if it works or not.

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