Questions and postings pertaining to the usage of ImageMagick regardless of the interface. This includes the command-line utilities, as well as the C and C++ APIs. Usage questions are like "How do I use ImageMagick to create drop shadows?".
fmw42
Posts: 25562 Joined: 2007-07-02T17:14:51-07:00Authentication code: 1152Location: Sunnyvale, California, USA
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by fmw42 2012-08-07T10:10:22-07:00
Your IM syntax is not correct for IM 6. try putting the image before the options.
convert "rgba.png" -alpha extract "alpha.png"
The quotes are not really needed unless you have a space in the file names, though it should not hurt to leave them.
see
http://www.imagemagick.org/Usage/basics/#why
fmw42
Posts: 25562 Joined: 2007-07-02T17:14:51-07:00Authentication code: 1152Location: Sunnyvale, California, USA
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by fmw42 2012-08-07T12:39:19-07:00
The image you posted has no alpha channel. Perhaps it got removed when uploading or I am not downloading correctly.
fmw42
Posts: 25562 Joined: 2007-07-02T17:14:51-07:00Authentication code: 1152Location: Sunnyvale, California, USA
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by fmw42 2012-08-07T16:17:33-07:00
You do not say what version of IM and platform you are using (or I missed it). But since IM 6.7.8.3 grayscale images have been linear rather than non-linear sRGB. So to get back what you expect you need to add -set colorspace RGB to your command as
lilith
Posts: 8 Joined: 2010-10-06T23:37:50-07:00Authentication code: 8675308
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by lilith 2012-08-07T22:12:26-07:00
Hello,
I'm using 6.7.8.8.
And thanks, it works perfectly
Greetings.
anthony
Posts: 8883 Joined: 2004-05-31T19:27:03-07:00Authentication code: 8675308Location: Brisbane, Australia
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by anthony 2012-08-07T22:43:12-07:00
Alpha channel is always linear, so I don't know why you need such a convoluted colorspace!
