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 coordi‐
       nates.  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'  chro‐
       maticity 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 us‐
       ing 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  chromatici‐
       ties  of  the  primary  illuminants and white point for the color system.  You can turn this off with op‐
       tions, though.

       ppmcie annotates the periphery of the color tongue with the wavelength, in nanometers of the monochromat‐
       ic 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 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 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 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 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)