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adding transparency to grayscale images?

https://imagemagick.com/discourse-server/viewtopic.php?t=9315

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Re: adding transparency to grayscale images?

Posted: 2007-07-27T04:43:22-07:00
by glennrp

Code: Select all

convert input.png -negate alpha.png
composite -compose copyopacity alpha.png input.png -depth 8 output.png
This results in an RGBA png file. I can't figure how to force Gray-alpha output,
so I use

Code: Select all

    pngcrush -c 4 output.png gray-alpha.png
afterwards if I need gray-alpha.
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