main block: [0,0] -> [160x120], pixel sum is 352458

split into:
0: [0,0] -> [80x60], pixel sum is 98391
1: [80,0] -> [80x60], pixel sum is 76070
2: [0,60] -> [80x60], pixel sum is 100715
3: [80,60] -> [80x60], pixel sum is 77282