I have a directory with 1350 PNG images with an indexed palette and a white background and I want to turn white into a transparent background like Gimp does: a light blue turns into a semi-transparent blue. That’s the idea.
So I read up on scripting a bit, I used the *Help* → *Procedure Browser*, and I wrote a little scheme function based on what I found online.
This is `~/.config/GIMP/2.10/scripts/white-to-transparent.scm`:
(define (batch-white-to-transparent pattern)
(let* ((filelist (cadr (file-glob pattern 1))))
(while (not (null? filelist))
(let* ((filename (car filelist))
(image (car (gimp-file-load RUN-NONINTERACTIVE
filename filename)))
(drawable (car (gimp-image-get-active-layer image))))
(gimp-layer-add-alpha drawable)
(plug-in-colortoalpha RUN-NONINTERACTIVE
image drawable "white")
(gimp-file-save RUN-NONINTERACTIVE
image drawable filename filename)
(gimp-image-delete image))
(set! filelist (cdr filelist)))))
And I invoke Gimp as follows in the directory where all the PNG files are:
gimp -i -b '(batch-white-to-transparent "*.png")' -b '(gimp-quit 0)'
It’s taking quite a while: about 1min/30 images, so I’m expecting 45min for all of them. Time for bed while this runs!
#Gimp
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⁂
I am sure ImageMagick would be the faster (and much easier to script) solution here:
convert image.png -transparent white result.png
– Andreas Gohr 2019-09-24 04:44 UTC
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In this case that isn’t true because I don’t just want to make white pixels transparent. I also want to make light blue pixels semi-transparent (these arise due to anti-aliasing of the original scan). The answer given on StackOverflow doesn’t look simple at all:
convert \
original.png \
\( \
-clone 0 \
-fill "#a0132e" \
-colorize 100 \
\) \
\( \
-clone 0,1 \
-compose difference \
-composite \
-separate \
+channel \
-evaluate-sequence max \
-auto-level \
\) \
-delete 1 \
-alpha off \
-compose over \
-compose copy_opacity \
-composite \
output.png
I don’t know whether it’d be faster, of course... 🙂
– Alex Schroeder 2019-09-24 20:27 UTC
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@Miredly said:
Wow, that is a hairy answer.
Generally, `convert <imagefile> -fuzz XX% -transparent <color> <resultfile>` works for me
When I said the same thing regarding partial transparency, Miredly said:
that’s what `-fuzz XX%` is for, the higher percentage, the larger the gradient of that color is effected
Maybe next time!
– Alex Schroeder 2019-09-25 05:13 UTC
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Gimp’s (tag(changethename) btw) color to alpha works much better for this particular purpose than Image Magick’s
– Sandra 2020-12-04 18:48 UTC
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@estebanm wrote GIMP Scripting.
– 2020-12-04 18:51 UTC
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Hello, I tried to execute your script but nothing happens and I just get 2 times the output “batch command executed successfully” in another window. Do you have any clue on this ? Sincerly
– Theo 2022-03-21 14:50 UTC
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Sadly, I have never used this again, so I do t know.
– Alex 2022-03-21 15:07 UTC