How to implement gray level probability density function?

the gray-level probability density function given as P(g) = h(g)/M, where h(g) is the number of pixels with gray level g and M is the total number of pixels in the image.

I want to implement this on a gray scale image, my question is what is h(g) in my case and what are gray level g... i know M is (row*colum) please answer

Answer 1

[Image Analyst]

% Get histogram:
[pixelCounts, grayLevels] = imhist(grayImage);
% Computer probability density function:
pdf = pixelCounts / numel(grayImage);

Answer 2

[Dishant Arora]

you can use built in function imhist.