Calculating black pixels in colour image

Hi, does anyone know how do I calculate black pixels in a colour image using Matlab? Thank you.

Answer 1

[Image Analyst]

Find pixels that are black in all three color channels. One way to do it is:

% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1) == 0;
greenChannel = rgbImage(:, :, 2) == 0;
blueChannel = rgbImage(:, :, 3) == 0;

blackPixelImage = redChannel & greenChannel & blueChannel;
numBlackPixels = sum(blackPixelImage(:));
message = sprintf('The number of pure black pixels = %d', numBlackPixels);
uiwait(helpdlg(message));

[Hui Shi Lim]

Thank you. But where is the line to add in my own picture in order to calculate it?

[Image Analyst]

I called your image rgbImage. What did you call it? In the line below:

rgbImage = imread(yourFileName);

what is the variable name you used instead of "rgbImage"? Whatever it is, that's what you'd use in my code.

By the way, you can also use the sum() function

blackPixelImage = sum(rgbImage, 3) == 0;
numBlackPixels = sum(blackPixelImage(:));
message = sprintf('The number of pure black pixels = %d', numBlackPixels);
uiwait(helpdlg(message));

[Hui Shi Lim]

Thank you:)

[Image Analyst]

You're welcome. If we're done here, can you mark the Answer as Accepted. Thanks in advance.