input: Image data stored in Portable Gray Map (PGM) format. Applicable to Mat only. Saving int, float or double matrices is a lossy operation, as each element is copied and converted to an 8 bit representation. As such the matrix should have values in the [0,255] interval, otherwise the resulting image may not display correctly. [auto_detect] 
output: pgm_binary
options: r a w _ a s c i i
options: r a w _ b i n a r y
options: a r m a _ a s c i i
options: a r m a _ b i n a r y
options: c s v _ a s c i i
options: h d f 5 _ b i n a r y
options: p g m _ b i n a r y
options: p p m _ b i n a r y