Attached Link: http://www.cambridgeincolour.com/tutorials/histograms1.htm

Hi Melem may be worth starting a thread of your own as it is not easy to answer it here as it depends on what colour space you are using But here is a good link:

Danny O'Byrne  http://www.digitalartzone.co.uk/

"All the technique in the world doesn't compensate for the inability to notice" Eliott Erwitt