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November 2009

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2009.11.20 17:01 "tiff 4.0 beta5 and YCbCr w jpeg compression question", by John Evans

I've a question about the code in tif_jpeg.c in beta-5.  The 
function "TIFFInitJPEG" has changed from 3.9.2 to beta-5 in that 3.9.2 has  
its last line reading 

        /*
         * Mark the TIFFTAG_YCBCRSAMPLES as present even if it is not
         * see: JPEGFixupTestSubsampling().
         */
        TIFFSetFieldBit( tif, FIELD_YCBCRSUBSAMPLING );

This is not present in beta-5, meaning that running tiffinfo in beta-5 
against, say, "quad-jpeg.tif" will not print the YCbCr subsampling 
coefficients.  The coefficients will print out, however, on "ycbcr-cat.tif" 
as that one has LZW compression instead of JPEG.  

If that line of code is added back in, tiffinfo will again print out the 
subsampling coefficients for quad-jpeg.tif, so I'm wondering if leaving that 
last line out was intentional or accidental?  If accidental, I'll be happy to 
file the bug report with patch.