How to count white pixels in Watershed segmented image?

Question

Tawsif Mostafiz 2021-8-4

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https://ww2.mathworks.cn/matlabcentral/answers/892247-how-to-count-white-pixels-in-watershed-segmented-image

评论： Image Analyst 2021-8-5

采纳的回答： Image Analyst

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I am using watershed method to this image:

And got the output:

Now I want to convert the segmented part within the yellow boundary to black and white, and calculate its white and black pixels within the boundary. How can I do it?

The part of the code is as follows:

[B,L]=bwboundaries(tumor,'noholes'); %draw boundaries around the tumor
imshow(image);
hold on
for i=1:length(B)
 plot(B{i}(:,2),B{i}(:,1), 'y' ,'linewidth',1.45);
 end
title('Segmented Tumor');
hold off;

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Answer 1

Image Analyst 2021-8-5

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https://ww2.mathworks.cn/matlabcentral/answers/892247-how-to-count-white-pixels-in-watershed-segmented-image#answer_761162

在 MATLAB Online 中打开

What is the intensity that distinguishes between your "black" and "white"? 128? Don't use image as the name of your variable -- it's already the name of a built-in function.

Anyway to get the pixel values for blob in L:

pixelValues = grayScaleImage(L == 1); % A 1-D vector of all the pixel values in the region.
% Then sum up black and white
threshold = 128; % Whatever you want.
numBlackPixels = sum(pixelValues < threshold)
numWhitePixels = sum(pixelValues >= threshold)

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Tawsif Mostafiz 2021-8-5

编辑：Tawsif Mostafiz 2021-8-5

在 MATLAB Online 中打开

@Image Analyst I have changed the code a little bit for better understanding. I have converted it to black and white using following:

bw=im2bw(grayScaleImage,0.15); %0.15 is the threshold value
[B,L]=bwboundaries(tumor,'noholes'); %draw boundaries around the tumor
imshow(bw);
hold on
for i=1:length(B)
 plot(B{i}(:,2),B{i}(:,1), 'r' ,'linewidth',1.45);
 end
title('Segmented Tumor');
hold off;

Now, the output is following:

Now, I want to count the white pixels and black pixels within the red border. Extremely sorry for being vague previously. How do I do that?

Image Analyst 2021-8-5

在 MATLAB Online 中打开

Try this:

thisBoundary = B{1}; % Whatever boundary you want.
x = thisBoundary(:, 2);
y = thisBoundary(:, 1);
redMask = poly2mask(x, y, rows, columns);
pixelsInRedMask = binaryImage(redMask);
numBlack = sum(pixelsInRedMask == 0);
numWhite = sum(pixelsInRedMask == 1);