[magick-users] RE: Need help covering up misalignment of RGB channels

[Fred Weinhaus]

I stand corrected by Anthony. The proper usage is:



convert example_rgb_gap.jpg \
           \( +clone -separate \
             -background white -compose darken -flatten \
             -threshold 0 \) \
           -compose multiply -composite example_rgb_gap_proc.jpg

Anthony's comments on my suggestion below - corrected above:

So not specifying      -background white
is NOT a good idea. Other wise it will default to the first images
background meta-data setting, or if not present, the IM default of
white.   In other words   DO NOT OMIT IT.

And yes while  -threshold 1  will generally work, especially for Q16,
where a value of '1' is even smaller than for a Q8 IM, but it is not
correct.  It was only correct for a VERY small version release, until IM
Examples picked up on the change.




>Actually there is a simpler way, thanks to Anthony Thyssen:
>
>convert example_rgb_gap.jpg \
>	\( +clone -separate -compose darken -flatten -threshold 1 \) \
>	-compose multiply -composite example_rgb_gap_proc3.jpg
>
>
>
>
>
>>try
>>
>>convert example_rgb_gap.jpg -separate example_rgb_gap_%d.png
>>convert example_rgb_gap_0.png example_rgb_gap_1.png \
>>	-compose darken -composite example_rgb_gap_01.png
>>convert example_rgb_gap_2.png example_rgb_gap_01.png \
>>	-compose darken -composite -threshold 1 example_rgb_gap_mask.png
>>convert example_rgb_gap.jpg example_rgb_gap_mask.png \
>>	-compose multiply -composite example_rgb_gap_proc.jpg
>>
>>
>>
>>
>>>The attachment on my last post didn't go through.  An example of what
>>>I am describing can be found here:
>>>
>>>http://www.magicpancakes.com/example_rgb_gap.jpg
>>>
>>>Hello all,
>>>I'm writing with what should be a relatively simple task.  I've never
>>>tried to do anything beyond simple conversions, resizing, composites,
>>>etc. using IM, so I'm sort of a newbie.
>>>I am starting with three individual images, representing R G and B
>>>bands that I combine into a single RGB image.  In the resulting
>>>image, the individual bands do not line up properly (an issue
>>>inherent in the individual bands, not anything that I can control).
>>>I've attached a small section as an example.
>>>I want to set the entire region to 0 while preserving the surrounding
>>>areas where the RGB pixel value is correct.  In other words, if the
>>>value is 0 on an individual band, it should be 0 in the final image.
>>>I have been playing with fx statements, but I'm having trouble with
>>>syntax, and it is SLOW.
>>>I know there must be a simple and FAST solution.  Perhaps creating a
>>>mask from the individual bands and then applying it over the RGB
>>>image?  I need to run this as a step in a script to process many of
>>>these images (~11 mb each).
>>>Thanks for any suggestions.