NAME

       ppmcie - draw a CIE color chart as a PPM image

SYNOPSIS

       ppmcie [-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.

DESCRIPTION

       ppmcie  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 chromaticity on the vertical scale.
       (You can choose alternatively 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-corrected.  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 example,
       monochromatic blue-green with a wavelength of 500nm cannot be represented in a PPM image.

       For these hues, ppmcie substitutes a similar hue as  follows:  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  specify 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 triangle 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  coordinates
       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  system.   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 color mapped device or file format, you'll need to use ppmquant
       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 broadcasting 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 Engineers (SMPTE)  in  standards  RP-37
                 and  RP-145, and -hdtv uses the much broader HDTV ideal primaries.  -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 selects 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 default 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 ALSO

       ppmdither(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 software 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 implied warranty.

                                       26th September 1994                              PPMCIE(1)