pamrecolor(1) - Man pages

Pamrecolor User Manual(1) General Commands Manual Pamrecolor User Manual(1)

NAME
pamrecolor - alter colors without affecting luminance

SYNOPSIS
pamrecolor [--colorspace=name] [--rmult=fraction] [--gmult=fraction]
[--bmult=fraction] [--targetcolor=color] [--colorfile=file] [-random-
seed=integer]

[infile]

Minimum unique abbreviation of option is acceptable. You may use double
hyphens instead of single hyphen to denote options. You may use white
space in place of the equals sign to separate an option name from its
value.

DESCRIPTION
This program is part of Netpbm(1).

pamrecolor changes an image's colors to be as close as possible to given
target colors but with the constraint that the luminance not be modi-
fied. That is, the original image and the target image will look iden-
tical if both are converted to grayscale (e.g. with ppmtopgm(1)). You
can have pamrecolor select target colors randomly, specify a single hue
for the entire image, or take the target colors from a target image.

In addition to real Netpbm images, pamrecolor works on pseudo-Netpbm im-
ages based on arbitrary color spaces. You can define the color space
explicitly or choose one of many that pamrecolor knows by name.

The output is a PAM image on standard output. Options control the exact
format of the PAM. If you want a PNM (PBM, PGM, or PPM) image, use pam-
topnm(1) on the output. There is no need to convert if you will use the
image as input to a current Netpbm program, but many other programs
don't know what a PAM is.

OPTIONS
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see ]8;;index.html#commonoptions\ Common Options]8;;\ ), pamrecolor recognizes the
following command line options:

--colorspace=name
Designate the color space to use for determining the contribution
to luminance of each of the red, green, and blue color channels.
For example, in the SMPTE-C color space an RGB color is converted
to grayscale by multiplying the red channel by 0.2124132, the
green channel by 0.7010437, and the blue channel by 0.0865432 and
summing the resulting three products.

When you use this option, the input and output images are not
true Netpbm images, because the Netpbm image format specifies a
particular color space. Instead, you are using a variation on
the format in which the sample values in the raster have differ-
ent meaning. Many programs that ostensibly use Netpbm images ac-
tually use a variation with a different color space. For exam-
ple, ]8;;http://www.gimp.org/\GIMP]8;;\ uses sRGB internally and if you have GIMP generate a
Netpbm image file, it really generates a variation of the format
that uses sRGB.

pamrecolor knows the following color spaces (name values):

adobe

Adobe RGB (1998) with a D65 reference white

apple

Apple RGB with a D65 reference white

cie

CIE with an Illuminant E reference white

ntsc

NTSC RGB with an Illuminant C reference white

pal

PAL/SECAM with a D65 reference white

smpte-c

SMPTE-C with a D65 reference white

srgb

sRGB with a D65 reference white

wide

Wide-gamut RGB with a D50 reference white

The default is "ntsc" because this is the color space that the
Netpbm formats and many graphics utilities use. As a counterex-
ample, ]8;;http://www.gimp.org/\GIMP]8;;\ uses sRGB as its native color space.

The luminance values pamrecolor uses for each of the above come
from Bruce Lindbloom's Computing RGB-to-XYZ and XYZ-to-RGB ma-
trices" (1) page.

--rmult=fraction

--gmult=fraction

--bmult=fraction
Instead of selecting a color space by name, you can specify ex-
plicitly the contribution of each color channel to the overall
luminance as red, green, and blue multipliers. These three op-
tions must be used together, and the three fraction values must
sum to 1.0. For example, you can specify the ProPhoto (ROMM) RGB
color space with "--rmult=0.2880402 --gmult=0.7118741
--bmult=0.0000857".

--targetcolor=color
Designate color as the target color for the image. pamrecolor
will make each pixel as close as possible to color subject to the
constraint that the luminance must stay the same as in the origi-
nal image. Specify color as in the ]8;;libnetpbm_image.html#colorname\argument of the pnm_parsec-
olor() library routine]8;;\ (e.g., "hotpink" or "#ff69b4").

If you specify neither --targetcolor nor --colorfile, pamrecolor
will randomly select a target color for each pixel of the input
image.

You may not specify both -targetcolor and -colorfile.

--colorfile=file
Take per-pixel target colors from Netpbm file file instead of us-
ing a single target color for the entire image. file should be a
PPM or color PAM image. If the image in the file wider or taller
than the input image, pamrecolor uses only the left and top part
of it. If the image is narrower or shorter, pamrecolor considers
the image to be repeated in a tile pattern.

If you specify neither --targetcolor nor --colorfile, pamrecolor
will randomly select a target color for each pixel of the input
image.

You may not specify both -targetcolor and -colorfile.

-randomseed=integer
This is the seed for the random number generator that generates
the pixels.

Use this to ensure you get the same image on separate invoca-
tions.

By default, pamrecolor uses a seed derived from the time of day
and process ID, which gives you fairly uncorrelated results in
multiple invocations.

This option was new in Netpbm 10.61 (December 2012).

EXAMPLES
This command tints an image yellow:

pamrecolor --targetcolor=yellow colorpic.pam > yellowpic.pam

This command takes the colors from colorpicture.ppm and applies them to
graypicture.pgm:

pamrecolor --colorfile=colorpic.ppm graypic.pgm > colorizedpic.pam

The grayscale version of colorizedpic.pam will look just like
graypic.pgm. Note that if you use a non-Netpbm tool to do the conver-
sion to grayscale, you may additionally need to specify an appropriate
--colorspace value for your conversion tool.

NOTES
Here are a couple of fun special effects you can produce with pamre-
color:

• Specify a color file that is identical to the input image but
with some large, colored text added to it. The text will "magi-
cally" vanish when the image is converted to grayscale.

• Provide a low-contrast grayscale image - perhaps a secret message
written in similar shades of gray - as the input file and a col-
orful but completely different image as the color file. If done
carefully, the grayscale image can be hidden by the colorful im-
age. Only people who know to convert the result to grayscale can
recover the original grayscale image.

• Use --targetcolor=tan to make an image look like an old-timey
photograph (or, more precisely, a ]8;;http://en.wikipedia.org/wiki/Photographic_print_toning\sepia-toned photograph]8;;\ of the
late 1800s).

HISTORY
Scott Pakin wrote pamrecolor in July 2010.

pamrecolor was new in Netpbm 10.52 (September 2010).