2005.05.02 16:12 "RE: [Tiff] 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