[Magick-bugs] Bug in convert: modulate is broken - introduces colour artefacts

[Richard Neill]

> Just to let you know, this bug is still present in the current release,
> which I downloaded and compiled today, namely:
>    Version: ImageMagick 6.4.4 2008-10-23 Q16 http://www.imagemagick.org
> 
> I also downloaded the latest beta, ImageMagick-6.4.5-0.tar.gz, and this 
> is also affected.
> 
> Is there anything else I can do to help fix it?

I've narrowed this down to a change that was made in between the 
following releases.

ImageMagick-6.3.9-10  - works correctly

ImageMagick-6.4.0-11  - is broken.

I can't be any more specific than that, since these are the two 
closest-spaced releases I find on this page: 
ftp://ftp.imagemagick.org/pub/ImageMagick/legacy/

Could someone who understands the ImageMagick internals take a look at 
this, please?

Thanks,

Richard



> 
> Thanks,
> 
> Richard
> 
> 
> On Fri, 17 Oct 2008, Richard Neill wrote:
> 
>> Dear developers,
>>
>> I've just upgraded from Mandriva 2008.1 to 2009.0, and now have a new
>> version of convert installed,
>>
>> -modulate now does something horrible to colours around areas of high
>> contrast, although it used to work just fine.
>>
>> Here is a sample image:
>>  http://richardneill.org/tmp/example.png
>>
>> And here is an invocation to show the bug:
>>  convert example.png -modulate 25 error.png
>>
>> Here is what I see as a result:
>>  http://richardneill.org/tmp/error.png
>>
>> Version: ImageMagick 6.4.2 2008-09-15 Q16 http://www.imagemagick.org
>> Copyright: Copyright (C) 1999-2008 ImageMagick Studio LL
>>
>> The application, btw, is a rather complicated script to generate
>> opening/closing titles for a video, and to provide a fade in from black
>> at the start. The expected output should be much darker than the input,
>> but should not have the ugly colour-errors.
>>
>> Thanks very much for your help,
>>
>> Richard
>>
>>
>>
>> P.S. Please consider adding a bugzilla for ImageMagick.
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>> Magick-bugs at imagemagick.org
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>>
> 
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