Fred Weinhaus on wrote...
|
| >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.
|
You can also do the modifications in one command, but joining these
operations together. I did this recently in the IM forums.
Here is a copy of the final... modify just the 'L' channel
command...
It splits up the image, clones the 'L' image into a separate
parenthesis, then swaps your changes for the original and
recombines them back together again.
convert $infile -colorspace HSL -channel RGB -separate +channel \
\( +clone ...L CHANNEL MODIFICATIONS HERE.... \
\) +swap +delete \
\( -clone 0 -colorspace HSL \
-clone 0 -compose CopyRed -composite \
-clone 1 -compose CopyGreen -composite \
-clone 2 -compose CopyBlue -composite \
\) -delete 0-2 -colorspace RGB $outfile
Unfortunately as you see above the IM -combine can NOT handle
combining non-RGB greyscale channel images. This is a known bug
that has been reported, but one not simple to fix, as IM needs
some way to determine what colorspace the greyscale channel images
need to produce.
I shall add the above to the IM Examples section...
Combining non-RGB Channel Images
http://www.imagemagick.org/Usage/channels/#combine_other
It should appear in a day or so.
Anthony Thyssen ( System Programmer ) <[EMAIL PROTECTED]>
-----------------------------------------------------------------------------
The Butterfly Effect :-
When a butterfly creating turbulence in England,
can cause a typhoon in Hong Kong! - "Chaos"
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Anthony's Home is his Castle http://www.cit.gu.edu.au/~anthony/
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