% imagehist1D
% usage: imagehist1D(pic) 
% read a jpeg image and split into three RGB components
% and show the histograms
% pic is the name of a jpg file given in 'filename.jpg' format
% typically the component images will be returned as matrices of byte-sized unsigned integers 
% allowing 256 levels for each colour, i.e., 24 bit colour
% Rmap, Gmap and Bmap are colormaps for showing the R,G,B components

function  imagehist1D(pic,numbins);

% load picture
[R,G,B,Rmap,Gmap,Bmap] = jpg2rgb(pic,'nopic');
Z = zeros(size(R));
mc = double(max([R(:);G(:);B(:)]));
[hR,xR] = hist(double(R(:)),numbins);
[hG,xG] = hist(double(G(:)),numbins);
[hB,xB] = hist(double(B(:)),numbins);
mh = max([hR(:);hG(:);hB(:)]);

% show images
figure(1)
clf
imshow(cat(3,R,G,B));
pause
figure(2)
clf
pause
subplot(2,3,1)
imshow(cat(3,R,Z,Z));
subplot(2,3,4)
bar(xR,hR,1.0,'r');
axis([0,mc,0,mh+10]);
pause
subplot(2,3,2)
imshow(cat(3,Z,G,Z));
subplot(2,3,5)
bar(xG,hG,1.0,'g');
axis([0,mc,0,mh+10]);
pause
subplot(2,3,3)
imshow(cat(3,Z,Z,B));
subplot(2,3,6)
bar(xB,hB,1.0,'b');
axis([0,mc,0,mh+10]);