Bug #68508 for Imager: error diffusion dither confusing with grey maps

Fri May 27 08:44:38 2011 TONYC [...] cpan.org - Ticket created

Subject:	error diffusion dither broken
Date:	Fri, 27 May 2011 22:44:27 +1000
To:	bug-Imager [...] rt.cpan.org
From:	tonyc [...] cpan.org

Translating an image with the error diffusion dither doesn't appear to be handled correctly. perl -MImager -MImager::Test=test_image -e '$im = test_image(); $im->write(file => "mono.gif", make_colors => "mono", translate => "errdiff") or die $im->errstr' produces a mostly black image, but there should be some shading over the green/red/blue filled areas.

Mon May 30 04:07:16 2011 TONYC [...] cpan.org - Subject changed from 'error diffusion dither broken' to 'error diffusion dither confusing with grey maps'

Mon May 30 04:07:16 2011 TONYC [...] cpan.org - Severity Normal added

Mon May 30 04:07:16 2011 TONYC [...] cpan.org - Broken in 0.83 added

Mon May 30 04:21:09 2011 TONYC [...] cpan.org - Correspondence added

The problem is the error only accumulates on the red channel, and since the channel is capped at 255, the black entry continues to match for the entire image. As a partial solution we can process the image as grayscale when the supplied palette is grayscale. This isn't a perfect solution, since the caller can still provide a palette that doesn't cover the gamut used in the image, but it does handle a common case.

Mon May 30 04:21:10 2011 TONYC [...] cpan.org - Status changed from 'new' to 'open'

Mon May 30 04:26:56 2011 TONYC [...] cpan.org - Correspondence added

Note: the conversion to greyscale isn't done for the other colour translators since they do no error propagation, so the current algorithm is enough.

Fri Jun 03 02:22:45 2011 TONYC [...] cpan.org - Status changed from 'open' to 'patched'

Tue Jun 21 09:44:13 2011 TONYC [...] cpan.org - Correspondence added

Fixed about as well as it can be in 0.84.

Tue Jun 21 09:44:13 2011 The RT System itself - Status changed from 'patched' to 'open'

Tue Jun 21 09:44:13 2011 TONYC [...] cpan.org - Status changed from 'open' to 'resolved'

Tue Jun 21 09:44:27 2011 TONYC [...] cpan.org - Fixed in 0.84 added