Mega pixel exceptions needed

[ideamonk]

from @meshaabi

nah i have 2.5 gigs ram free.. source is 500 images.. worked with -z 2

btw was checking out the src.. you are checking every pixel on the image.. the index builder died when i tried to use the 7.1 megpix pics from my camera..

maybe could check pixel blocks or first generate a thumbnail itself before getting to average pixel counting