problem in the code,getting following error

for i=1:256
  img_hist(i)=sum(sum(im==(i)));
end

In an assignment A(:) = B, the number of elements in A and B must be the same.

Error in ==> kmeansclustering at 7 img_hist(i)=sum(sum(im==(i)));

Answer 1

[Image Analyst]

Why not just use imhist():

[counts, grayLevels] = imhist(im);

If you have to do it your way, try this and see how the times compare:

im=randi(256, [1000,1000]) - 1;
% Horribly inefficient way of getting histogram:
img_hist = zeros(1,256);
tic;
for i=0:255
  img_hist(i+1)=sum(sum(im==i));
end
toc;

% Less inefficient way (more than 10 times faster)
img_hist = zeros(1,256); % Reset
tic
[rows, columns] = size(im);
for col = 1 : columns
  for row = 1 : rows
    img_hist(im(row,col)+1) = img_hist(im(row,col)+1) + 1;
  end
end
toc

% Best way is to use imhist()
  tic
  img_hist = imhist(im);
  toc;

Elapsed time is 0.479380 seconds.
Elapsed time is 0.047586 seconds.
Elapsed time is 0.008468 seconds.

Now, which way do you think is best? That is, simplest and fastest?

Answer 2

[Azzi Abdelmalek]

clear img_hist 
for i=1:256
  img_hist{i}=sum(sum(im==(i)));
end