Hi,
I would like to write a script for an advanced 'Unsharp Mask'
technique, which I need very frequently. This technique requires
the image to be available in HSL color space (which is no problem),
but then only the 'L' channel shall be modified. How does one go
about there using ImageMagick?
TIA,
Claus
Hello Claus,
I have done similar kinds of things with only the L channel from HSL.
See my scripts: omnistretch, redist, bcimage at:
http://www.fmwconcepts.com/imagemagick/index.html
Here is what I have done:
Separate channels:
convert $infile -colorspace HSL -channel R -separate $tmp0
convert $infile -colorspace HSL -channel G -separate $tmp1
convert $infile -colorspace HSL -channel B -separate $tmp2
Do your unsharp masking processing on $tmp2
The recombine channels
convert $tmp0 -colorspace $colormodel $tmp0 -compose CopyRed -composite \
$tmp1p -compose CopyGreen -composite \
$tmp2p -compose CopyBlue -composite \
-colorspace RGB $outfile
$tmp0, $tmp1, $tmp2 are predefined temporaries that the script will
automatically delete when the script finishes.
I learned all this from Anthony Thyssen. Anthony has explained this
conversion on his page at
http://www.imagemagick.org/Usage/channels/
see especially the section on Combining non-RGB Channel Images
When you finish your script, I would like to see what you are doing,
if it is not a private thing. I assume you are doing unsharp masking
on just the L channel, but I would like to understand what more you
might be doing in addition.
Fred
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