Hoe to find histogram count

I'm working on CBIR using entropy, where entropy of an image can be calculated using formula -sum(p.*log2(p)). where 'p' defines histogram count of an image. MATLAB has an inbuilt command _histc_to find histogram count, and the syntax is histc(x,edge,dim) and I'm not getting what edge is, I've a bitmap image x for which i need to find histogram count. what is 'p' ? is it a vector or a matrix?

Answer 1

[Image Analyst]

Then why not use imhist():

[pixelCount, grayLevel] = imhist(grayImage, 256);

With histc(), you have to define the edges and it bins everything in between the edges. The equivalent to imhist() might be

edges = -0.5 : 1.0 : 255.5; % Edges for a grayscale image.
[pixelCount, grayLevel] = histc(grayImage, edges);