Histogram for a 3D grayscale image

I need to find out the normalized histogram ( or histogram) for a 3D graylevel image.

I tried using the following (imHistogram) function

http://www.mathworks.in/matlabcentral/fileexchange/28681-imhistogram/content/imHistogram.m

But it gives the result in the form of a 1x256 array, but being a 3D image, I want the result in the form of a 256x256 array.

Anyway, anyone could help with this.