Re: tiff:photometric and CCITT compression

On Wed, 11 Oct 2023, frechefuchs via Graphicsmagick-help wrote:

> Am 11.10.23 um 00:05 schrieb frechefuchs via Graphicsmagick-help:
>
>> When creating images with IM and option -define
>> quantum:polarity=min-is-black, I get the expected output of tiffinfo
>> and with the image viewers I've tried I couldn't observe an inverted
>> image (ristretto, geeqie, gthumb, eog, eom).
> I see an inverted image created by IM requesting min-is-white explicitly:
>
>> $ convert logo: -monochrome -define quantum:polarity=min-is-white miw.tif
>
>
> But I think this is a bug in IM.  Byte-wise comparing two images with
> min-is-white and min-is-black photometric interpretation (switching
> compression off), the two files seem to only differ in the
> PhotometricInterpretation tag.  That is, image data is actually
> min-is-black encoded in both cases.

Have you tested if GM is able to successfully write min-is-white via 
libtiff by modifying GM code (as you had suggested)?  It is useful to 
verify that libtiff does not reject it as an illegal case.

The utilities/tests/gen-tiff-images/genimages script which is included 
in the GM source tree could be updated to also include compressed 
variants.  It already generates 5568 files without even including 
compression.

Bob
-- 
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
Public Key,     http://www.simplesystems.org/users/bfriesen/public-key.txt