How to count the number of black and white pixels (linux, imagemagik, etc)

Question

I have black and white images (see below). How count white and black pixels (as example 30% black and 70% white, or 123456 black pixels and 39393 white pixels)?

p.s. I work in linux, what i must use? imagemagick? i prefer a command line interface program.

Answer 1

If all your pixels are either black or white, you can calculate the mean pixel brightness using ImageMagick and then multiply it by the number of pixels in the image (width x height):

convert bw.gif -format "%[nint(fx:mean*w*h)]" info:
182138

If you want the number of white and number of black pixels in two shell variables, you can do this:

read white black < <(convert bw.gif -format "%[fx:mean*w*h] %[fx:(1-mean)*w*h]" info:)

echo $white,$black
182138,153985

Answer 2

You can use ImageMagick's histogram function to get a pixel count for each color in the image. Using your image as an example:

$ convert XPH7c.gif -define histogram:unique-colors=true \
> -format %c histogram:info:-
    153985: (  0,  0,  0,255) #000000 black
    182138: (255,255,255,255) #FFFFFF white

So, your image has 153985 black pixels, and 182138 white pixels.