Convert a PNG image to a Netpbm image. See also:
pamtopng
. More information: https://netpbm.sourceforge.net/doc/pngtopam.html.
pngtopam path/to/image.png > path/to/output.pam
pngtopam -alphapam path/to/image.png > path/to/output.pam
pngtopam -mix -background color path/to/image.png > path/to/output.pam
pngtopam -text path/to/file.txt path/to/image.png > path/to/output.pam