paminvert
produces a negative of a PAM or PNM image by inverting all pixel values
TLDR
Invert image colors
$ paminvert [input.pam] > [output.pam]
Invert from pipe$ cat [image.ppm] | paminvert > [inverted.ppm]
SYNOPSIS
paminvert [pamfile]
DESCRIPTION
paminvert produces a negative of a PAM or PNM image by inverting all pixel values. Each sample value is replaced with maxval minus the sample value.
For grayscale, black becomes white and vice versa. For color, each channel is inverted independently.
EXAMPLE
$ # Create negative
paminvert photo.ppm > negative.ppm
# Invert and convert to PNG
paminvert photo.ppm | pnmtopng > negative.png
paminvert photo.ppm > negative.ppm
# Invert and convert to PNG
paminvert photo.ppm | pnmtopng > negative.png
FORMULA
$ output = maxval - input
For 8-bit (maxval=255):
Black (0) -> White (255)
White (255) -> Black (0)
Gray (128) -> Gray (127)
For 8-bit (maxval=255):
Black (0) -> White (255)
White (255) -> Black (0)
Gray (128) -> Gray (127)
CAVEATS
Simple inversion; not perceptual negative. Alpha channel also inverted if present.
HISTORY
paminvert is part of Netpbm, providing simple image inversion as a fundamental operation.