CODEWITHSUNDEEP
linuximagegraphicsimagemagick
Anton Shevtsov
Anton Shevtsov

Reputation: 1299

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

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.

sample

Upvotes: 10

Views: 5697

Answers (4)

aw2014
aw2014

Reputation: 11

A less smart, but more intuitive option:

$ convert XPH7c.gif XPH7c.txt

$ grep "white" XPH7c.txt | nl | tail -1

182138 514,632: (255,255,255,255) #FFFFFF white

$ grep "black" XPH7c.txt | nl | tail -1

153985 530,632: ( 0, 0, 0,255) #000000 black

Explanation:

1) Convert gif file to txt file (human readable list providing each pixel coordinate and respective color)

0,0: ( 0, 0, 0,255) #000000 black

1,0: ( 0, 0, 0,255) #000000 black

2,0: (255,255,255,255) #FFFFFF white

(...)

530,632: ( 0, 0, 0,255) #000000 black

2) List all "black" and "white" pixels using grep (display only last line info with tail -1)

3) Additional step -- Display only the desired data using awk or other similar tool

$ grep "black" XPH7c.txt | nl | tail -1 | awk '{print $8 ": " $1}'

black: 153985

Upvotes: 1

Mark Setchell
Mark Setchell

Reputation: 208003

Another way to do this is to clone the image and set all the pixels in the cloned image to black, then calculate the Absolute Error with respect to the original image like this:

convert XPH7c.gif \( +clone -evaluate set 0 \) -metric AE -compare -format "%[distortion]" info:
182138

That tells you that there are 182,138 pixels in the original image that differ from the totally black cloned image, i.e. 182,138 non-black (white) pixels.

Upvotes: 1

Mark Setchell
Mark Setchell

Reputation: 208003

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

Upvotes: 6

Markus Iturriaga
Markus Iturriaga

Reputation: 176

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.

Upvotes: 10

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