Re: TIFF compression support list

On Thu, 28 Sep 2023, frechefuchs via Graphicsmagick-help wrote:
>
> Hm, either I did something stupid or that doesn't work.  With the
> attached patch, the build indicates LZW support, and I am able to create
> an LZW compressed image.  At least tiffdump shows a compression tag 5
> and file size is between RLE and Zip compression.
>
> What is the expected result of requesting a non-existent compression type?

I seem to be continually providing bad advice. ;-(

So now that I am editing files, and actually testing, I see a better 
way, and you should like it quite a lot more, except that it won't 
remove LZW from the claimed compression algorithms.

Around line 419, you should find a function called 
CompressionSupported().  For "case LZWCompression" do this:

     case LZWCompression:
       {
#if 0
         strlcpy(compression_name,"LZW",MaxTextExtent);
#if defined(COMPRESSION_LZW)
         compress_tag=COMPRESSION_LZW;
         status=MagickTrue;
#endif
#endif
         break;

It seems that I assumed that many compressors (especially those 
provided directly by libtiff) are always available.

Test the result like this:

   ./rungm.sh ./utilities/gm convert logo: -compress lzw -debug coder crap.tiff

The above will also show traces describing what it is doing.

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