How to count number of red, blue and green pixels in image.

Hi,

I woud like to know, how can I count number of red, blue and green pixels in image.

Thanks in advance

[DGM]

In order to do that, you must first define what "red", "green" and "blue" mean in your context. That depends on the images and the intent.

[John D'Errico]

Pixels are almost never fully red, green, or blue. And what you might call red, green, or blue might not be what I would call those colors. So a slightly orangish red, is it still a red pixel? How far does it need to deviate into orange, before it stops being red? Maybe you use the supreme court definition of such a thing: that is, you know what red is when you see it.

You probably need to think about these questions before proceeding.

[Walter Roberson]

If RGB components are integers 0 to 255, then is [1 0 0] red? That is, the smallest change towards red away from black: does that count as red, or does it count as black? It has red component but not green or blue... under some definitions that would have to count as red.

rng(12345);
Z = zeros(48, 64, 3, 'uint8');
r = randi(size(Z,1),1,1);
c = randi(size(Z,2),1,1);
Z(r, c, 1) = 1;
image(Z)
title('which is the Red pixel?')

fprintf('Red pixel is at x = %d y = %d\n', c, r);

Red pixel is at x = 21 y = 45

Personally I cannot detect the red pixel until you get up to around 40 instead of 1