png-bw — convert a Portable Networks Graphics (PNG) format file to a BW format
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 > file.bw
will equally blend the red and blue color planes.
png-bw bw_file.png < file.bw
will convert a b/w PNG file to bw(5) format.
png-bw -R0.30 -G0.59 -B0.11 < file.png > file.bw
has the same effect as the -ntsc flag.
[The
-crt
weights are: 0.26, 0.66, 0.08]