local histograms - recomputing histograms for all parts of the image - Matlab - image

Question

i already have this:
function [h] = histImage (img)
nPix = numel(img);
h = accumarray( img (:)+1 , ones(nPix,1)/nPix, [256 1] , #sum,0)
this function will return a grayscale histogram for a given img into a 1X256 vector
now i want to build this function:
input: img - grayscale image matrix in rage [0..255]
windowSize - a 1x2 array [r c] rows and cols.
output: histArray 3d matrix for every i,j the 1D array histArray(i,j,:) is the histogram of img of the size WindowSize whose top left corner is (i,j)
function [histArray] = localHistograms (img,windowSize)
histArray = zeros(windowSize(1),WindowSize(2),256);
for i = 1:windowSize(1)
for j = 1:windowSize(2)
histArray(i,j,:) = histImage(img( i:windowSize(1), j:windowSize(2) ))
end
end
end
this is what i have so far can u please tell me my mistake?
how can i check my mistakes ? just enter some random images?

Answer 1

ok so my friend help me figuring out my mistake here is the working and tested code:
function [ histArray ] = localHistograms ( img,windowSize )
% Given an image returns a 3D array of histograms –
% one histogram per window in image.
% Input:
% img - a grayscale image in the range [0..255]
% windowSize – a 1x2 array [r c] defining the num rows and num cols
% of image windows.
% Output:
% histArray – an NxMx256 array.
%
% For every (i,j) the 1D array histArray(i,j,:) is the histogram
% of an image window of size windowSize whose top left corner
% pixel is (i,j). Histograms of windows that exceed the boundary
% of the of img are not included in histArray (thus N = number of
% rows of img less the number of rows of window +1.
% Similarly M=size(img,2)-windowSize(2)+1 ).
%
% Method: Scans the img pixel by pixel. For each scanned pixel,
% determines the histogram of the image window starting at the
% pixel and extending windowSize(1) rows and windowSize(2).
N = size(img,1) - windowSize(1) + 1;
M = size(img,2) - windowSize(2) + 1;
histArray = zeros(N ,M,256);
for i = 1:N
for j = 1:M
histArray(i,j,:) = histImage(img(i:i+windowSize(1)-1,j:j+windowSize(2)-1));
end
end
end