Is there an open-source program that'll extract the color from an image?

Question

I'm looking for something like what Windows 8+ uses for "Automatic" coloring, or the new YouTube Android app uses for its userpage nav bars, where the app automatically looks at the picture and return a palette of main and compliment colors.

Does any such program or API exist that is also open-source?

Answer 1

I am not aware what Windows 8 or new YouTube app does, since I do not use either, but if you want to get an N-colours palette sorted by frequency, i. e. you seeking how to get from image.png:

a palette.png:

or palette.txt:

#D2615E
#B24953
#DE8D75
#5D133B
#65214C
#D36F6D
#EECAAA
#DCA295
#C78E79
#8F283D
#CEB3B6
#99364B
#A36A90
#A95D6B
#7B4886
#75416E

then it’s quite a basic task for any image processing tool.

That how it could be done with ImageMagick (plus a bit of GNU Bash, Coreutils and AWK):

$ convert "image.png" -colors 16 -depth 8 -format '%c' histogram:info:- \
    | sort --reverse --numeric-sort \
    | gawk 'match ($0, /^ *[0-9]+: \([^)]+\) (#[0-9A-F]+) .+$/, a) { print a[1] }' \
    | tee "palette.txt" \
    | while read colour; do convert -size 20x20 "xc:$colour" +depth miff:-; done \
    | montage - -geometry +0+0 "palette.png"

That’s an example, of course; you have not to exec convert and monage via system(3) call from your program – interfaces for ImageMagick are available for all popular languages: C, C++, Perl, Python, Ruby, Java, etc. And it is a free/libre software (covered by Apache v2 license, to be precise).

Answer 2

There are a lot - probably one of the easiest is ImageMagik convert, e.g.:

  convert rose: \
          -define histogram:unique-colors=false \
          histogram:histogram.gif

Which gives, in this case for the rose image:

You can do similar things in a number of FOSS image processing programs such as GIMP, G'IMIC, Darktable...

You can also do this sort of things with python tools, etc.