Please can you tell me Algorithm to count the number of white pixel ?

i want algorithm to count the number of white pixels, please .

[Walter Roberson]

Greyscale image or black and white or color image?

[Malak s]

color image, RGB

Answer 1

[Image Analyst]

How do you define "white". Have you checked out my color segmentation demos in my File Exchange? http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862

In the special specific case where you have a gray scale image (not color) and want to just count the number of pixels at exactly 255, you can do this:

whitePixels = grayImage == 255; % Produces a binary (logical) image.
count = sum(whitePixels(:))

[Malak s]

i want for color image

[Image Analyst]

I covered both cases in my answer - gray scale and color. Did you see the link for color segmentation? I can't give a specific answer because you did not define white. What is YOUR definition of white? Is (255,255,255) white? Sure, but what about (255,255,254)? Is that white? What about (231,233,232)? Is that white? What about the onion in the MATLAB peppers.png demo image which has a big variety of RGB levels. Is that white? Or just part of it white? You have to have a numerical definition of white. You can't just simply say "I want white" - it's not precise enough. Does that explain it better?

[Malak s]

oh sorry , yes that is , white (255,255,255)

[Image Analyst]

Same basic concept that I showed you for grayscale, you just need to AND them together:

% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
% Find out where all three channels are 255, not just 1 or 2 of them.
whitePixels = redChannel    == 255 & ...
              greenChannel  == 255 & ...
              blueChannel   == 255; % Produces a binary (logical) image.
count = sum(whitePixels(:))

[Malak s]

thank you ..

[Jotheeshwar V]

When I am using this code, there is an error showing

Index exceeds matrix dimensions.

Error in Try_03_07_2018 (line 17) greenChannel = color(:, :, 2);

Please Help me out of this.

[Image Analyst]

Your image is not a color image. So just do

greenChannel = color;

[Jotheeshwar V]

 %
imread color.jpg
load color.jpg
redChannel = color(:, :, 1);
greenChannel = color(:, :, 2);
blueChannel = color(:, :, 3);
whitePixels = redChannel    == 255 & ...
              greenChannel  == 255 & ...
              blueChannel   == 255; 
count = sum(whitePixels(:));
Red1Pixels = redChannel    == 255 & ...
              greenChannel  == 166 & ...
              blueChannel   == 166;
count = sum(Red1Pixels(:));
Red2Pixels = redChannel    == 254 & ...
              greenChannel  == 85 & ...
              blueChannel   == 82; 
count = sum(Red2Pixels(:))
Blue1Pixels = redChannel    == 179 & ...
              greenChannel  == 169 & ...
              blueChannel   == 250; 
count = sum(Blue1Pixels(:))
Blue2Pixels = redChannel    == 255 & ...
              greenChannel  == 255 & ...
              blueChannel   == 255; 
count = sum(Blue2Pixels(:))

This my complete code.

This might be useful for you people to help me.

-Jotheeshwar

[Jan]

See Jotheeshwar V's thread: https://www.mathworks.com/matlabcentral/answers/408785-how-to-count-the-number-of-pixels-from-an-image-for-specifies-colors

Answer 2

[Walter Roberson]

In a greyscale image, every pixel that is not absolute black is arguably white of some brightness or other. Therefore you can count the number of non-zero pixels to get the answer. Fortunately, MATLAB has a call nnz() that does that for you.

[Walter Roberson]

sum(all(reshape(YourImage,[],3) == 255, 2))

[Malak s]

thank you ..