You need to create a histogram for each channel seperatetly
function hst = im2hsvHist( img )
%
% computes three channels histogram in HSV color space
%
n = 256; % number of bins per hist (per channel)
hsvImg = rgb2hsv( img );
hst = zeros(n,3);
for ci = 1:3
hst(:,ci) = imhist( hsvImg(:,:,ci ) , n );
end
hst = hst(:) ./ n; % to 3*n vector, normalize by n and not 3n
Using this function you can compute the image to image distance in hsv space
Im1 = imread(filename1);
hst1 = im2hsvHist(Im1);
Im2 = imread(filename2);
hst2 = im2hsvDist(Im2);
f = norm( hst1 - hst2 );
Sneak a peek for a vectorized version of im2hsvHist
:
n = 256;
hsvImg = rgb2hsv( img );
hst = hist( reshape(hsvImg, [], 3), 255 ); % instead of loop!
hst = hst(:) / n;