how to compute number of pixels in images

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Medical Imaging
Medical Imaging 2017-7-28
评论： Image Analyst 2017-7-28
Dear sir I have one ground truth image(image 1) and other segmented image(image 2). I want to compute the number of pixel for white area for image 1 and number of pixel for red area in image 2. and then want to compute the difference of pixels.
  2 个评论
Adam
Adam 2017-7-28
If the black pixels are all 0s then just use
doc nnz
If they aren't you can still just easily count, for example
nnz( myImage == 7 )
Gianfrancesco Angelini
Gianfrancesco Angelini 2017-7-28
There are many ways to do it. I will suggest you a basic one, hoping to be clearer and helpful
% Define your images
img1 = x1;
img2 = x2;
% Convert them in grayscale, easier approach
img1g = rgb2gray(img1);
img2g = rgb2gray(img2);
figure(); imshow(img1g); %if you want to see the result
figure(); imshow(img2g); %if you want to see the result
% Calculate
img1g_totpx = numel( img1g ); %total number of pixel of img1
img1g_NB = length( img1g(img1g~=0) ); %number of pixel not black of img1
img2g_totpx = numel( img2g ); %total number of pixel of img2
img2g_NB = length( img2g(img2g~=0) ); %number of pixel not black of img2
diffPx = abs( img1g_NB - img2g_NB ); %difference of pixels between the 2 imgs
Cheers

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Image Analyst
Image Analyst 2017-7-28
Because a different person asked this very same question with the very same image, and Walter answered it here I'm thinking it's homework. I've tagged it as such.
http://www.mathworks.com/matlabcentral/answers/8626-how-do-i-get-help-on-homework-questions-on-matlab-answers
  2 个评论
Image Analyst
Image Analyst 2017-7-28
Oh, you're right. He posted it in someone else's discussion. I just saw the original poster's name.

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