“png” saves a PNG format image file of the current display.

png filename [, width [, height [, dpi [, ray]]]]

filename = string: file path to be written

width = integer: width in pixels {default: 0 (current)}

height = integer: height in pixels {default: 0 (current)}

dpi = float: dots-per-inch {default -1.0 (unspecified)}

ray = 0 or 1: should ray be run first {default: 0 (no)}

png image.png 
png image.png, dpi=300 

PNG is the only image format supported by PyMOL.

mpng | save | cmd.png | commands