adding transparency to grayscale images?

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glennrp
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Joined: 2006-04-01T08:16:32-07:00
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Re: adding transparency to grayscale images?

Post 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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