digits: 1797 images of 8x8 = 64 pixels
k =  2: variance kept  28.5%, mean squared pixel error  13.42
k =  5: variance kept  54.5%, mean squared pixel error   8.54
k = 10: variance kept  73.8%, mean squared pixel error   4.91
k = 20: variance kept  89.4%, mean squared pixel error   1.98
k = 30: variance kept  95.9%, mean squared pixel error   0.77
k = 64: variance kept 100.0%, mean squared pixel error   0.00
3-NN on all 64 pixels: accuracy 0.985,  19.8 ms per 540 images
3-NN on 20 components: accuracy 0.981,  14.5 ms per 540 images
