PPMCIE(1)PPMCIE(1)NAMEppmcie - draw a CIE color chart as a PPM image
SYNOPSISppmcie [-rec709|-cie|-ebu|-hdtv|-ntsc|-smpte] [-xy|-upvp]
[-red rx ry] [-green gx gy] [-blue bx by] [-white
wx wy] [-size edge] [-xsize|-width width]
[-ysize|-height height] [-noblack] [-nowpoint]
[-nolabel] [-noaxes] [-full]
All options can be abbreviated to their shortest unique
prefix.
DESCRIPTIONppmcie creates a PPM file containing a plot of the CIE
``tongue'' color chart -- to the extent possible in a PPM
image. Alternatively, creates a pseudo-PPM image of the
color tongue using RGB values from a color system of your
choice.
The CIE color tongue is an image of all the hues that can
be described by CIE X-Y chromaticity coordinates. They
are arranged on a two dimensional coordinate plane with
the X chromaticity on the horizontal axis and the Y chro
maticity on the vertical scale. (You can choose alterna
tively to use CIE u'-v' chromaticity coordinates, but the
general idea of the color tongue is the same).
Note that the PPM format specifies that the RGB values in
the file are from CIE Rec. 709 color system, gamma-cor
rected. And positive. See ppm(5) for details. If you
use one of the color system options on ppmcie, what you
get is not a true PPM image, but is very similar. If you
display such ppmcie output using a device that expects PPM
input (which includes just about any computer graphics
display program), it will display the wrong colors.
However, you may have a device that expects one of these
variations on PPM.
In every RGB color system you can specify, including the
default (which produces a true PPM image) there are hues
in the color tongue that can't be represented. For exam
ple, monochromatic blue-green with a wavelength of 500nm
cannot be represented in a PPM image.
For these hues, ppmcie substitutes a similar hue as fol
lows: They are desaturated and rendered as the shade where
the edge of the Maxwell triangle intersects a line drawn
from the requested shade to the white point defined by the
color system's white point. Furthermore, unless you spec
ify the -full option, ppmcie reduces their intensity by
25% compared to the true hues in the image.
ppmcie draws and labels the CIE X-Y coordinate axes unless
you choose otherwise with options.
ppmcie draws the Maxwell triangle for the color system in
use on the color tongue. The Maxwell triangle is the tri
angle whose vertices are the primary illuminant hues for
the color system. The hues inside the triangle show the
color gamut for the color system. They are also the only
ones that are correct for the CIE X-Y chromaticity coordi
nates shown. (See explanation above).
ppmcie also places a mark at the color system's white
point and displays in text the CIE X-Y chromaticities of
the primary illuminants and white point for the color sys
tem. You can turn this off with options, though.
ppmcie annotates the periphery of the color tongue with
the wavelength, in nanometers of the monochromatic hues
which appear there.
Finally, ppmcie displays the black body chromaticity curve
for Planckian radiators from 1000 to 30000 kelvins on the
image.
You can choose from several standard color systems, or
specify one of your own numerically.
CIE charts, by their very nature, contain a very large
number of colors. If you're encoding the chart for a col
or mapped device or file format, you'll need to use pp
mquant or ppmdither to reduce the number of colors in the
image.
OPTIONS
-rec709|-cie|-ebu|-hdtv|-ntsc|-smpte
Select a standard color system whose gamut to
plot. The default is -rec709, which chooses CIE
Rec. 709, gamma-corrected. This is the only
color system for which ppmcie's output is a true
PPM image. See explanation above. -ebu chooses
the primaries used in the PAL and SECAM broad
casting standards. -ntsc chooses the primaries
specified by the NTSC broadcasting system (few
modern monitors actually cover this range).
-smpte selects the primaries recommended by the
Society of Motion Picture and Television Engi
neers (SMPTE) in standards RP-37 and RP-145, and
-hdtv uses the much broader HDTV ideal pri
maries. -cie chooses a color system that has
the largest possible gamut within the spectrum
of the chart. This is the same color system as
you get with the -cie option to John Walker's
cietoppm program.
-xy plot CIE 1931 x y chromaticities. This is the
default.
-upvp plot u' v' 1976 chromaticities rather than CIE
1931 x y chromaticities. The advantage of u' v'
coordinates is that equal intervals of distance
on the u' v' plane correspond roughly to the
eye's ability to discriminate colors.
-red rx ry
specifies the CIE x and y co-ordinates of the
red illuminant of a custom color system and se
lects the custom system.
-green gx gy
specifies the CIE x and y co-ordinates of the
green illuminant of the color system and selects
the custom system.
-blue bx by
specifies the CIE x and y co-ordinates of the
blue illuminant of the color system and selects
the custom system.
-white wx wy
specifies the CIE x and y co-ordinates of the
white point of the color system and selects the
custom system.
-size edge
Create a pixmap of edge by edge pixels. The de
fault is 512x512.
-xsize|-width width
Sets the width of the generated image to width
pixels. The default width is 512 pixels. If
the height and width of the image are not the
same, the CIE diagram will be stretched in the
longer dimension.
-ysize|-height height
Sets the height of the generated image to height
pixels. The default height is 512 pixels. If
the height and width of the image are not the
same, the CIE diagram will be stretched in the
longer dimension.
-noblack Don't plot the black body chromaticity curve.
-nowpoint Don't plot the color system's white point.
-nolabel Omit the label.
-noaxes Don't plot axes.
-full Plot the entire CIE tongue in full intensity;
don't enhance the gamut of the specified color
system.
SEE ALSOppmdither(1), ppmquant(1), ppm(5)AUTHOR
Copyright (C) 1995 by John Walker (kelvin@fourmilab.ch)
WWW home page: http://www.fourmilab.ch/
Permission to use, copy, modify, and distribute this soft
ware and its documentation for any purpose and without fee
is hereby granted, without any conditions or restrictions.
This software is provided ``as is'' without express or im
plied warranty.
26th September 1994 PPMCIE(1)
