Counting the number of black pixels in an image

Question

Jonathan Maness 2020-4-3

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https://ww2.mathworks.cn/matlabcentral/answers/515225-counting-the-number-of-black-pixels-in-an-image

评论： Jonathan Maness 2020-4-4

Hello, I need help counting the number of black pixels in an image that was just taken through a camera. My current program is able to take an image and then convert the image into a black and white image based on the colors in the first image. I need to count the amount of black pixels in the processed image that was just taken that only contains black and white pixels. If it helps, here is my code so far (P.S. This includes some code that I have commented out to get the program working to this point):

clc
clear
clear all
images= []
webcamlist()
cam= webcam(1)
preview(cam)
pause(2);
images= snapshot(cam)
imshow(images)
r_channel= images(:,:,1);
g_channel= images(:,:,2);
b_channel= images(:,:,3);
images(:,:,1) =0;
images(:,:,3) = 0;
image(images);
mask= g_channel > 100, b_channel > 800, r_channel < 800, b_channel < 0, r_channel < 0;
imshow(mask)
 gr_ratio = double(g_channel)./double(r_channel);
 gb_ratio = double(g_channel)./double(b_channel);
 rb_ratio = double(r_channel)./double(b_channel);
 
% gr_ratio(isnan(g_ratio))=0;
% grayImage = rgb2gray(image);
% binaryImage = grayImage > 20;
% binaryImage = bwareaopen(binaryImage, 50);
% binaryImage = imfill(binaryImage, 'holes');
% grayImage(~binaryImage) = 0;
falseMatrix= zeros(7,7);
targetMatrix= ones(7,7);
checkMatrix= ones(7,7);
if targetMatrix == checkMatrix
%     cam = camStop;
    return
end

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Answer 1

Image Analyst 2020-4-4

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https://ww2.mathworks.cn/matlabcentral/answers/515225-counting-the-number-of-black-pixels-in-an-image#answer_423882

在 MATLAB Online 中打开

If "mask" is the image you want to count black pixels in, you can either do it like this:

numBlackPixels = numel(mask) - nnz(mask)

or like this:

numBlackPixels = sum(~mask(:))

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Image Analyst 2020-4-4

在 MATLAB Online 中打开

For others, he probably did:

fprintf('mask has %d black pixels.\n', numBlackPixels);
[rows, columns, numberOfColorChannels] = size(mask);
fprintf('mask has %d rows and %d columns.\n', rows, columns);

Jonathan Maness 2020-4-4

The If statement at the end of my original code was messing it up, so all I had to do was get rid of the entire if statement and then add in the line of code that you have me.

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