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)