How to count the number of white pixels

filename = 'untitled.jpg';

I = imread(filename);

figure, imshow(I);

sum(I(:) == 255)

ans = 592185

and

filename = 'untitled2.jpg';

I = imread(filename);

figure, imshow(I);

sum(I(:) == 255)

ans = 626229

....

This is strange that figure1 has much lower white pixels, because i'm agricultural student, so i do not know well about matlab, coding,,,

What is wrong about my script??

Answer 1

[Chunru]

First, you should use gray scale image.

Second you have a large white margin in your data (which is not seen from imshow). You can see the margin if you use imagesc instead.

If you need to count the white pixels inside. You can clip the image to remove the white margin first.

filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/996375/image.jpeg';
I = imread(filename);
I = rgb2gray(I);
figure, imagesc(I); colorbar; %imshow(I);

sum(I(:) >= 250)

ans = 199547

sum(I(200:600, 200:600)>250, 'all')

ans = 583

figure; histogram(I(:))

%whos
filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/996380/image.jpeg';
I = imread(filename);
I = rgb2gray(I);
figure, imagesc(I); colorbar; %imshow(I);

figure; histogram(I(:))

sum(I(:) >= 250)

ans = 211979

sum(I(200:600, 200:600)>250, 'all')

ans = 12900

[윤주 황]

Thank you for your answer, and i will try this script.

I'v got one more question.

I have to calculate <stained(fig1) pixels /flesh pixels(fig2)>.

According to your answers, <stained(fig1) pixels /flesh pixels(fig2) = 583/12900 >,, is that right??

[Chunru]

You are right.