png-bw — convert a Portable Networks Graphics (PNG) format file to a BW format


png-bw [-ntsc ] [-crt ] [ -R [num]] [ -G [num]] [ -B [num]] [in.png] >


png-bw will convert a PNG format file from its standard input and produce a black and white bw(5) file on its standard output, If the PNG file contains a B/W image the conversion is direct, however, if the PNG file contains a color image, then by default all three colors are weighted equally. The -ntsc uses weighting based on the NTSC primaries and the D6500 alignment white. The -crt flag applies weights for "typical" CRT phosphor chromaticities and the D6500 white.

Individual color plane(s) can be selected via the -R -G and -B flags. If one or more of these flags is followed by a value, the value will be treated as a weight to be applied to that color This value is implicitly 1.0 divided by the number of colors selected for the flags which are not followed by a value.


png-bw -R -B < file.png >

will equally blend the red and blue color planes.

png-bw bw_file.png <

will convert a b/w PNG file to bw(5) format.

png-bw -R0.30 -G0.59 -B0.11 < file.png >

has the same effect as the -ntsc flag.

[The -crt weights are: 0.26, 0.66, 0.08]


brlcad(1), png-pix(1), bw-png(1), pix-png(1), pix(5), bw(5)


John R. Anderson


This software is Copyright (c) 1998-2016 by the United States Government as represented by U.S. Army Research Laboratory.


Reports of bugs or problems should be submitted via electronic mail to <>.