Why does my image break apart into all sorts of shapes?

i take an image and change to cmyk

then split channels

then I want to change each to a bitmap

from bitmap halftone screen/ set the angle ( ie cyan: 85.  Screen to 15) ( like for silk screen)

then change bitmap to grayscale------at this point the image barracks up into all sorts of shapes.

also so when I simply want enlarge an image using the keyboard shortcuts of command + the image breaks up as well.