-evaluate-sequence mean creates transparent image

[wheany]

I have this base image:

Using this command:

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convert base.png ( -size 100x100 xc: +noise Random ) -evaluate-sequence mean base-noise.png

Creates this image:(It's transparent)
After I remove the alpha channel, I see that the image was exactly what I wanted:

If I instead use this command:

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convert base.png ( -size 100x100 xc: +noise Random ) -append base-noise-appended.png

I get this image: (again, exaclty what I expected)

Is this a bug or have I misunderstood something in how evaluate-sequence works?

[wheany]

Version info:

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>convert -version
Version: ImageMagick 6.7.6-5 2012-04-04 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2012 ImageMagick Studio LLC
Features: OpenMP

[fmw42]

I can confirm your result on IM 6.7.6.5 Q16 Mac OSX Snow Leopard.

Your base image has an alpha channel that is totally opaque, and thus not relevant, but is confusing the -evualuate-sequence.

Workaround is:

convert 1base.png \( -size 100x100 xc: +noise Random \) -alpha off -evaluate-sequence mean 1base-noise2.png

It won't hurt for any image that has no alpha channel or has a fully opaque alpha channel.

Nevertheless, it is a bug in my opinion.

[anthony]

Note: insteed of using -size 100x100 xc: you could have used +clone instead

To make it easier for testing here I use a bulti-in image to show the problem...

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convert rose: -alpha set \( +clone +noise Random \) \
                -evaluate-sequence mean   show:

More than likely it is a bug in handling of an images ALPHA, like Noise is assuming only RGB channels.
That I thought may have been a bug in -channel handling, something I experienced when I created -sparse-colors operator.

To me it seems like -evaluate-sequence needs to be expaned beyond just an assumed RGB channels but to all active channels. I have other notes in that Subtract, Multiply and Divide is also rather usless in its current implementation.
See IM Examples, Layering Images, evaluate-seqence
http://www.imagemagick.org/Usage/layers ... e-sequence

ASIDE: to Cristy. in IMv7 you also get a transparent image but not perfectly transparent, I see some minor garbage as well, indicating uncleared alpha channel memory!

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magick rose: -alpha set \( +clone +noise Random \) \
         -evaluate-sequence mean -background black -alpha remove show:

Which indicates memory clearing failure as well.

I have made a note of these problems. But I am not planning making option changes until I finished IMv7 scripting development (alpha).