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PNG-BW(1)

NAME

png-bw - convert a PNG (Portable Network Graphics) file to a BW (black and white) file

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SYNOPSIS

png-bw [-v] [-ntsc] [-crt] [-R[#]] [-G[#]] [-B[#]] [in.png] > out.bw

DESCRIPTION

png-bw reads a PNG image from the named file (or from standard input if no file is given) and writes a single-channel bw(5) image to standard output. If the input is already grayscale the data is passed through directly; if the input is a color image it is reduced to black and white.

By default all three color planes are weighted equally. The -ntsc flag applies the standard NTSC luminance weights based on the NTSC primaries and the D6500 white. The -crt flag applies weights for typical CRT phosphor chromaticities and the D6500 white.

Individual color planes can be selected with the -R, -G, and -B flags. If a flag is immediately followed by a value, that value is used as the weight applied to that plane. A selected plane with no explicit weight is implicitly given a weight of 1.0 divided by the number of selected planes.

OPTIONS

-v

Verbose. Report the color type, bit depth, image dimensions, gamma, background color, interlacing, and any text or timestamp metadata to standard error.

-ntsc

Use NTSC luminance weights (red 0.30, green 0.59, blue 0.11).

-crt

Use typical CRT phosphor weights (red 0.26, green 0.66, blue 0.08).

*-R*[#]

Select the red plane, optionally with an explicit weight (e.g. -R0.30).

*-G*[#]

Select the green plane, optionally with an explicit weight (e.g. -G0.59).

*-B*[#]

Select the blue plane, optionally with an explicit weight (e.g. -B0.11).

EXAMPLES

Example 1. Convert a color rendering to grayscale and view it
png-bw -ntsc render.png > render.bw
bw-pix render.bw | pix-fb -w 512 -n 512

Reduces a color PNG to a perceptually weighted grayscale bw(5) image using NTSC luminance weights, then converts it back to pix(5) and displays it on a framebuffer with pix-fb(1).

Example 2. Blend selected color planes with custom weights
png-bw -R0.30 -G0.59 -B0.11 file.png > file.bw

Combines the red, green, and blue planes with the given weights; this produces the same result as the -ntsc flag. Selecting planes without weights, as in png-bw -R -B file.png, blends those planes equally.

SEE ALSO

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

AUTHOR

BRL-CAD Team

This software is Copyright (c) 1998-2026 by the United States Government as represented by U.S. Army Research Laboratory.

BUG REPORTS

Reports of bugs or problems should be submitted via electronic mail to devs@brlcad.org