[SOLVED] Replace existing colour with a transparent colour

[gubi]

Hi all,
I have a transparent png file and I want to replace an existing opaque colour (eg. #000) with a transparent rgba colour (eg. rgba(255, 0, 0, 50.0)). Is it possible?
I spent days without result.
Here the command I use:

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convert -fuzz 100% img_black.png -alpha on -fill 'rgba(255, 0, 0, 50.0)' -opaque '#000' image_red.png

Please, anyone can help me?
Thanks in advance

[fmw42]

try reading the input first, then use opaque black. Also alpha is specified in the range of 0 to 1, not 0 to 100 or 0 to 255. So if you want 50% transparent use 0.5

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convert img_black.png -fuzz 100% -alpha on -fill 'rgba(255, 0, 0, 0.5)' -opaque '#000' image_red.png

or if that does not work, then

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convert img_black.png -fuzz 100% -alpha on -fill 'rgba(255,0,0,0.5)' -opaque '#000000FF' image_red.png

Please always provide your IM version and platform when asking questions on this forum.

[gubi]

Hi,
thanks for your reply.
First of all, sorry for my forgetfulness.

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$ convert -version
Version: ImageMagick 6.8.9-9 Q16 x86_64 2017-07-31 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2014 ImageMagick Studio LLC
Features: DPC Modules OpenMP
Delegates: bzlib cairo djvu fftw fontconfig freetype jbig jng jpeg lcms lqr ltdl lzma openexr pangocairo png rsvg tiff wmf x xml zlib

My OS is Ubuntu Linux 16.04

I tried your commands simply by copy-paste but without success.
This is the black image:


This is the output of the fist command:

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convert img_black.png -fuzz 100% -alpha on -fill 'rgba(255, 0, 0, 0.5)' -opaque '#000' image_red.png

And this is the output of the second command:

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convert img_black.png -fuzz 100% -alpha on -fill 'rgba(255,0,0,0.5)' -opaque '#000000FF' image_red.png

I expecting something like this:


Important: I opened the output image with Gimp and the color profile is "indexed...". Is it possible to assign an RGB color profile to the output?

Thanks

[fmw42]

Your image is totally black with a binary alpha channel. So one way is to make it totally red with an alpha channel reduced by 50%. This works for me on IM 6.9.9.8 Q16 Mac OSX. Change my path to your path to your sRGB.icc profile

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convert img_black.png -alpha off -fill red -opaque black -alpha on -channel a -evaluate multiply 0.5 +channel -profile /Users/fred/images/profiles/sRGB.icc image_red_half_alpha.png

This also works. Add -channel rgba from my earlier suggested command.

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convert img_black.png -alpha on -channel rgba -fill 'rgba(255,0,0,0.5)' -opaque '#000000FF' -profile /Users/fred/images/profiles/sRGB.icc image_red_half_alpha.png

[gubi]

Thanks!
The first command works as well.
The colour profile is downloadable from here: http://archive.ubuntu.com/ubuntu/pool/m ... ig.tar.bz2

Thanks a lot.
Gubi