Re: Bug with B&W conversion

On Thu, 6 Jan 2011, Andrew Stonewall wrote:

> I'm getting lots of weird conversion corruptions with GraphicsMagick when I convert to B&W.
> 
> For example if I do the following conversion:
> 
> "c:\Program Files\GraphicsMagick-1.3.12-Q16\gm.exe" convert -monochrome -format tif -compress group4 original.tif
> error.tif
> 
> with the files found here:
> 
> error.tif = http://www.mediafire.com/?9g6g74m3t5eg4f5
> 
> original.tif = http://www.mediafire.com/?f65syy6gzdah45h
> 
> You will notice that error.tif comes out chopped in half.  Other images sometimes come out all white - but large
> (expanded - bloated) i.e. the Group4 TIF is larger than an uncompressed MONO BMP should be.

This is facinating.  The issue seems to be related to storing the 
unassociated alpha channel in the image (original.tif has an 
unassociated alpha channel).  The problem goes away if you add +matte 
like this:

   gm convert -monochrome -compress group4 +matte original.tif crap.tif

It is not clear if this is due to a bug in GM, or a bug in libtiff. 
I am tending to suspect an issue in libtiff since there is no problem 
without the compression.  It is not normal to store an alpha channel 
in group3 or group4 compressed images (but should be possible).

Bob
-- 
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

------------------------------------------------------------------------------
Learn how Oracle Real Application Clusters (RAC) One Node allows customers
to consolidate database storage, standardize their database environment, and, 
should the need arise, upgrade to a full multi-node Oracle RAC database 
without downtime or disruption
http://p.sf.net/sfu/oracle-sfdevnl

_______________________________________________
Graphicsmagick-bugs mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/graphicsmagick-bugs