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ppmcie - draw a CIE colour chart in a portable pixmap
ppmcie
[-noblack] [-nowpoint] [-interpwp] [-full] [-cie|-ebu|-hdtv |-ntsc|-smpte] [-red rx
ry] [-green gx gy] [-blue bx by] [-white wx wy] [-size edge] [-xsize|-width width]
[-ysize|-height height]
ppmcie creates a portable pixmap containing
a plot of the CIE ``tongue'' colour chart, showing the colour gamut of either
a standard or user-specified colour system, annotated with axes, a mark
indicating the white point of the colour system, and the black body chromaticity
curve for Planckian radiators from 1000 to 30000 kelvins. The axes are
labeled with the CIE X and Y coordinates, the periphery of the tongue is
annotated with the wavelength of light, in nanometres, of the pure hues
which appear there, and the black body chromaticity curve is marked with
the temperature in kelvins.
CIE charts, by their very nature, contain a
very large number of colours. If you're encoding the chart for a colour
mapped device or file format, you'll need to use ppmquant or ppmdither to
reduce the number of colours in the image.
- -cie|-ebu|-hdtv|-ntsc|-smpte
- Select
a standard colour system whose gamut (the area inside the triangle formed
by the three primary colours) and white point are plotted within the CIE
tongue chart. The default is -ebu, 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 uses the CIE RGB primaries with
wavelengths of 700 nm, 546.1 nm, and 438.8 nm respectively; the CIE white
point is defined by equal R, G, and B intensities.
- -red rx ry
- specifies the
CIE x and y co-ordinates of the red illuminant of a custom colour system
and selects the custom system.
- -green gx gy
- specifies the CIE x and y co-ordinates
of the green illuminant of the colour system and selects the custom system.
- -blue bx by
- specifies the CIE x and y co-ordinates of the blue illuminant
of the colour system and selects the custom system.
- -white wx wy
- specifies
the CIE x and y co-ordinates of the white point of the colour 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.
- -nowhite
- Don't plot the colour system's white point.
- -full
- Plot the entire CIE
tongue in full intensity; don't enhance the gamut of the specified colour
system.
- -interpwp
- Interpolate out-of-gamut colours using the colour system's
white point as the origin of the interpolation line. By default, the white
defined by an equal mix of the three primaries is used.
All flags can be
abbreviated to their shortest unique prefix.
Obviously, colours outside
the gamut of the device used to view or print the CIE chart cannot be rendered
accurately. Colours outside the Maxwell's triangle formed by the three illuminants
are desaturated and rendered as the shade where the edge of the gamut triangle
intersects a line drawn from the requested shade to the white point defined
by an equal mixture of the illuminants (or the colour system's white point,
if -interpwp is specified). These out of gamut colours are drawn ``subdued''
at 3/4 the intensity of the shades within the gamut unless the -full switch
is specified, in which case in-gamut and out of gamut colours are not distinguished.
ppmdither(1)
, ppmquant(1)
, ppm(5)
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.
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