ppmcie



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 dimen-
       sional  coordinate plane with the X chromaticity on the horizontal axis
       and the Y chromaticity 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-corrected.  And positive.  See
       ppm(5) for details.  If you use one of the color system options on ppm-
       cie, 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
       ian 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 col-
       ors.  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  de-
                 fault  is -rec709, which chooses CIE Rec. 709, gamma-correct-
                 ed.  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  stan-
                 dards.   -ntsc  chooses  the  primaries specified by the NTSC
                 broadcasting system (few modern monitors actually cover  this
                 range).   -smpte selects the primaries recommended by the So-
                 ciety 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 chro-
                 maticities.  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 illumi-
                 nant 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
                 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, with-
       out any conditions or restrictions.  This  software  is  provided  ``as
       is'' without express or implied warranty.



                              26th September 1994                    PPMCIE(1)
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