lesto:
if you want a suggestion, use a more powerful MCU if you need something serious.
Thank your for such a quick answer 
! I'm actually thinking about reading all pixels, this is the huge problem..
I'll probably be adding a 23K256 32k SRAM chip to store pixel values and an external 14-bit ADC in order to get a good read, I chose Arduino because of its simplicity + built-in USB interface, I can't find a similar product for such a cheap price..