http://docs.opencv.org/3.1.0/d1/db7/tutorial_py_histogram_begins.html https://schneide.wordpress.com/2012/06/18/basic-image-processing-tasks-with-opencv/ http://www.pyimagesearch.com/2014/01/27/hobbits-and-histograms-a-how-to-guide-to-building-your-first-image-search-engine-in-python/ http://www.pyimagesearch.com/2014/01/22/clever-girl-a-guide-to-utilizing-color-histograms-for-computer-vision-and-image-search-engines/ http://www.weheartcv.com/pixel-counting-color-statistics-part-1/ https://github.com/rossgoodwin/hmap (convers one image histrogram to another one)
https://luminous-landscape.com/wp-content/uploads/2004/08/dark-light.jpg http://answers.opencv.org/question/62479/determining-if-a-color-image-is-overexposed-or-underexposed/
http://dx.doi.org/10.1016/j.jcp.2005.06.012 ..... https://engineering.ucsb.edu/~cse/Files/distributiondistance042.pdf
http://www.itl.nist.gov/div898/handbook/eda/section3/eda35f.htm