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2005.05.02 16:12 "Re: Color TIFF/JPEG compression questions", by Jason Frank
Interesting, since my vendor is having trouble producing conforming
images, I took one of the images out of the libtiff image test pack,
v3.4pics.tar.gz. I converted it to what I need to test with by doing
the follwing:
tiff2rgba -c jpeg -r 16 quad-jpeg.tif quad-jpeg-rgb.tif
This gave me a file with the following tags:
tiffinfo quad-jpeg-rgb.tif
TIFF Directory at offset 0xdb28
Image Width: 512 Image Length: 384
Bits/Sample: 8
Compression Scheme: JPEG
Photometric Interpretation: RGB color
Extra Samples: 1<assoc-alpha>
YCbCr Subsampling: 2, 2
Orientation: row 0 top, col 0 lhs
Samples/Pixel: 4
Rows/Strip: 16
Planar Configuration: single image plane
Software: LIBTIFF, Version 3.7.2
Copyright (c) 1988-1996 Sam Leffler
Copyright (c) 1991-1996 Silicon Graphics, Inc.
JPEG Tables: (289 bytes)
My source image has these tags:
TIFF Directory at offset 0x5b6e
Image Width: 512 Image Length: 384
Position: 0, 0
Bits/Sample: 8
Compression Scheme: JPEG
Photometric Interpretation: YCbCr
YCbCr Subsampling: 2, 2
Samples/Pixel: 3
Rows/Strip: 16
Planar Configuration: single image plane
Reference Black/White:
0: 0 255
1: 128 255
2: 128 255
JPEG Tables: (574 bytes)
It looks like tiff2rgba retained the YCbCr field. And, for some reason
the source file has JPEG Tables, which I thought were used under Type 6
compressions. I don't know if that's expected, but I thought I'd pass
it on.
I was able to convert it to PDF using pdflib3, and view it in Acrobat
Reader. I can also view the converted TIF successfully in irfanView,
but not in MS' current viewer (whatever they're using now...) I also
dropped the alpha channel, but that didn't appear to make any
difference. I'm betting that MS might be having trouble with either the
YCbCr subampling or the JPEG tables. Don't know much for sure anymore
though.
Jason