# How to count the number of white pixels

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윤주 황 on 13 May 2022
Commented: Chunru on 13 May 2022
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??
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### Accepted Answer

Chunru on 13 May 2022
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
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Chunru on 13 May 2022
You are right.

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