[magick-users] "-channel A -fx intensity" using -evaluate?

[Anthony Thyssen]

David Vanderson on  wrote...
| Hello,
| 
| A few weeks ago we were doing cloud composition, which is close to 
| something that I've been doing - setting the alpha channel of each pixel 
| to the intensity of each pixel.  Anthony asked why we were using -fx, 
| which is slow, instead of -evaluate.
| 
| I confess that I've tried and failed a few times to figure out how to do 
| this with -evaluate.  Can anyone enlighten me?
| 
| Thanks,
| Dave

Note   -channel A  -fx  intensity
was being used to mapp a greyscale to the alpha channel.


Try this instead.

 convert  image.png  -colorspace gray \
          -background white -channel A -combine   ouptut.png

This command makes the input image greyscale.
It then makes that greyscale image a 'transpaency' channel setting
all other color channels to pure white.   That is it is now a white
image with various shades of transparency.

If this is NOT what you want, then me more specific.


  Anthony Thyssen ( System Programmer )    <A.Thyssen at griffith.edu.au>
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