How to count the number of occurrences of pixel intensities in an image without using for loop?

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Mohana Singh
Mohana Singh 2018-9-7
编辑： Stephen23 2018-9-7
I am to write a script for histogram equalisation and I need to work on each RGB plane separately. In the first step I count the number of occurrences of each intensity value in the range 0-255. As far as I know, using for loops makes MATLAB code super slow.
org_image = imread('image.jpg')
tot_pixel = size(org_image,1) * size(org_image,2)
R = org_image(:,:,1);
G = org_image(:,:,2);
B = org_image(:,:,3);
[R_val_ocurr,R_unique_val] = histcounts(R);
[G_val_ocurr,G_unique_val] = histcounts(G);
[B_val_ocurr,B_unique_val] = histcounts(B);
Now to have an array of size 256,with each index holding number of pixels corresponding to it what should my next step be? I'm trying to write down my logic :
for i = 0 to 255
if i is in R_unique_val
hist[i] = R_val_ocurr[i]
else
hist[i] = 0
Please tell me how to correctly and efficiently write this.
  1 个评论
Stephen23
Stephen23 2018-9-7
This is confusing, because the first part of your code gets a histogram, in fact your even write this "In the first step I count the number of occurrences of each intensity value in the range 0-255". So each of R_val_ocurr, etc. is a histogram. Then what else do you have to do?

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Stephen23
Stephen23 2018-9-7
编辑：Stephen23 2018-9-7
im = imread('image.jpg');
Rhist = imhist(im(:,:,1));
Ghist = imhist(im(:,:,2));
Bhist = imhist(im(:,:,3));
Or using histcounts:
Rhist = histcounts(im(:,:,1),0:256);
Ghist = histcounts(im(:,:,2),0:256);
Bhist = histcounts(im(:,:,3),0:256);

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