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2005.06.07 18:43 "Group4 compression & alpha channel", by Bob Friesenhahn
2005.06.07 19:15 "Re: Group4 compression & alpha channel", by Andrey Kiselev
2005.06.07 19:29 "Re: Group4 compression & alpha channel", by Bob Friesenhahn

2005.06.07 18:43 "Group4 compression & alpha channel", by Bob Friesenhahn

It has been observed that when GraphicsMagick writes a min-is-black 
TIFF image with Group4 compression and an alpha channel (as an extra 
sample) that the right half of the image is lost.  The image 
description is:

TIFF Directory at offset 0x0
   Image Width: 207 Image Length: 167
   Bits/Sample: 1
   Sample Format: unsigned integer
   Compression Scheme: CCITT Group 4
   Photometric Interpretation: min-is-white
   Extra Samples: 1<unspecified>
   FillOrder: msb-to-lsb
   Orientation: row 0 top, col 0 lhs
   Samples/Pixel: 2
   Rows/Strip: 167
   Planar Configuration: single image plane
   DocumentName: muki.tif
   Software: GraphicsMagick 1.2 unreleased Q16 http://www.GraphicsMagick.org/

I strongly suspect that this loss of data is due to libtiff but have 
not done a thorough investigation yet to make absolutely sure.  The 
same occurs when using FAX compression.

By simply not requesting Group4 or FAX compression, the file is saved 
and read ok.  This works:

TIFF Directory at offset 0x0
   Image Width: 207 Image Length: 167
   Bits/Sample: 1
   Sample Format: unsigned integer
   Compression Scheme: None
   Photometric Interpretation: min-is-black
   Extra Samples: 1<unspecified>
   FillOrder: msb-to-lsb
   Orientation: row 0 top, col 0 lhs
   Samples/Pixel: 2
   Rows/Strip: 157
   Planar Configuration: single image plane
   DocumentName: muki.tif
   Software: GraphicsMagick 1.2 unreleased Q16 http://www.GraphicsMagick.org/

Are there any known issues in libtiff with this scenario?

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