ppmgamma
TLDR
Apply gamma correction
$ ppmgamma [2.2] [input.ppm] > [output.ppm]
Lighten image$ ppmgamma [0.5] [input.ppm] > [output.ppm]
Darken image$ ppmgamma [2.0] [input.ppm] > [output.ppm]
Per-channel gamma$ ppmgamma [1.0] [1.2] [1.0] [input.ppm] > [output.ppm]
SYNOPSIS
ppmgamma gamma [ppmfile]
ppmgamma rgamma ggamma bgamma [ppmfile]
DESCRIPTION
ppmgamma applies gamma correction to a PPM image. Gamma < 1 lightens the image, gamma > 1 darkens it. Each pixel value is raised to the power of 1/gamma.
Part of Netpbm toolkit.
PARAMETERS
gamma
Gamma value for all channels.rgamma, ggamma, bgamma
Per-channel gamma values.
EXAMPLES
$ # Standard gamma correction
ppmgamma 2.2 image.ppm > corrected.ppm
# Lighten dark image
ppmgamma 0.5 dark.ppm > lighter.ppm
# Darken bright image
ppmgamma 2.0 bright.ppm > darker.ppm
# Adjust blue channel only
ppmgamma 1.0 1.0 1.3 image.ppm > blue_adjusted.ppm
# Reverse gamma
ppmgamma 0.45 linear.ppm > srgb.ppm
ppmgamma 2.2 image.ppm > corrected.ppm
# Lighten dark image
ppmgamma 0.5 dark.ppm > lighter.ppm
# Darken bright image
ppmgamma 2.0 bright.ppm > darker.ppm
# Adjust blue channel only
ppmgamma 1.0 1.0 1.3 image.ppm > blue_adjusted.ppm
# Reverse gamma
ppmgamma 0.45 linear.ppm > srgb.ppm
GAMMA VALUES
$ < 1.0 - Lighten midtones
= 1.0 - No change
> 1.0 - Darken midtones
2.2 - Typical monitor gamma
= 1.0 - No change
> 1.0 - Darken midtones
2.2 - Typical monitor gamma
CAVEATS
Use pamgamma for more features. Values at 0 and max unchanged. Part of Netpbm.
HISTORY
ppmgamma is part of Netpbm by Jef Poskanzer, implementing gamma correction for images.
SEE ALSO
pamgamma(1), ppmbrighten(1), pnmgamma(1), netpbm(1)
