change image load from 3ch to 1ch

[dhpollack]

This addresses issue #55. One expects a 1 channel mask (resize based only on height and width) but you force this to become a 3 channel mask upon loading (mode="RGB"). Now we correctly get a 1 channel 8 bit mask.

[wesleyw72]

Good work but I think this is a duplicate of #33.

[dhpollack]

Kind of. But he assumes the image is a 32 bit encoding and I'm assuming it's 8 bit (which is more typical in ML).

[dhpollack]

pillow mode docs

[dhpollack]

gonna close, reopen if you want to add it.