i have written code for histogram am getting this error ?? Input argument "I" is undefined.

% takes a 2D array (or image) I as input and returns
% an image of the same type that has undergone histogram
% equalization using n bins and has a range of outputs 
% that spans the range between min and max.

% O - output histogram equalized image
function [O] = histoeq(I, n, min, max)

[h,bins] = histogram(I, n, min, max);

O = zeros(size(I));
imcdf = 0;
for i=1:n-1
  index = ((I>=bins(i)) .* (I<bins(i+1))) == 1;
  imcdf = imcdf + h(i);
  O(index) = max*imcdf;
end
% handle the last bin:
index = ((I>=bins(n)) .* (I<=max)) == 1;
imcdf = imcdf + h(n);
O(index) = max*imcdf;

O = uint8(O); % for imshow...

Answer 1

[Walter Roberson]

Exactly how are you starting the function executing? When you have a function with parameters, you cannot start it by pressing an F* key or clicking on a menu item: instead you need to go down to the command line and type in the command indicating the parameters you are passing in.

Answer 2

[Image Analyst]

The Image Processing Toolbox already has this useless function. It's called histeq(). Why don't you just use that? Like I said, it's pretty much useless for a number of reasons but it's there. For educational purposes I guess. Kind of like Otsu thresholding done by graythresh() - usually useless but it's simple and easy and taught about in schools so they put it in. I never use it. There's a locally adaptive histogram equalization version that isn't useless and sometimes finds use for background correction. It's called adapthisteq().