The parameters for contrast were taken out of two images: a person in front of water(1) and a waterfall in the forest(2):

pool.map seems to have problems calculating pool.map(lambda x:f(x,a,b,c),list) for fixed a,b,c. The following Error occurs: cPickle.PicklingError: Can't pickle <type 'function'>: attribute lookup builtin.function failed In this case the function partial should be used [1]

Also working with a Queue an Processes got stuck sometimes (larger images)

Times for Calculating in parallel or not (as comments in code):

parallel single load time: 0.0821390151978 find heal time: 5.16196799278 heal time: 4.91810297966

single load time: 0.167742013931 find heal time: 1.17766499519 heal time: 5.1039288044

parallel batch load time: 0.0962250232697 find heal time: 1.56606888771 heal time: 5.10925316811

batch load time: 0.0910410881042 find heal time: 1.09560799599 heal time: 5.1529481411 total 877 circles

[1] https://stackoverflow.com/questions/5442910/python-multiprocessing-pool-map-for-multiple-arguments