Re: TIFF compression support list

Am 28.09.23 um 20:23 schrieb Bob Friesenhahn:
> On Thu, 28 Sep 2023, frechefuchs via Graphicsmagick-help wrote:
> 
> except that it won't remove LZW from the claimed compression
> algorithms.

If that list mirrors libtiff capabilities as compiled from source I
think that is OK.  At least much better than a static list that I was
assuming.


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

That works.


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

That seems to be the case.  In a WEBP-disabled build, I can create WEBP
compressed TIFF images with a compression value of 50001 (0xc351).  (A
value that I have not been able to find any specification for, so far.)
Which is counter-intuitive, but libtiff seems to provide its own
compression routines.


> 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.

That's an interesting tool!

Thanks!
fux