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September 2006

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2006.09.26 04:45 "Tiffcrop beta available for testing", by Richard Nolde
2006.09.26 04:55 "Re: Tiffcrop beta available for testing", by Bob Friesenhahn
2006.09.26 05:17 "Re: Tiffcrop beta available for testing", by Joris Van Damme
2006.09.26 05:43 "Re: Tiffcrop beta available for testing", by Joris Van Damme
2006.09.27 04:21 "YCbCr data in tiffcrop", by Richard Nolde
2006.09.27 12:50 "Re: YCbCr data in tiffcrop", by Joris Van Damme

2006.09.26 04:55 "Re: 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/