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1 perry 1 PPMCIE
2 !!!PPMCIE
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 OPTIONS
7 SEE ALSO
8 AUTHOR
9 ----
10 !!NAME
11
12
13 ppmcie - draw a CIE color chart as a PPM image
14 !!SYNOPSIS
15
16
17 __ppmcie__
18 [[__-rec709__|__-cie__|__-ebu__|__-hdtv__|__-ntsc__|__-smpte__]
19 [[__-xy__|__-upvp__] [[__-red__ ''rx ry'']
20 [[__-green__ ''gx gy''] [[__-blue__ ''bx by'']
21 [[__-white__ ''wx wy''] [[__-size__ ''edge'']
22 [[__-xsize__|__-width__ ''width'']
23 [[__-ysize__|__-height__ ''height'']
24 [[__-noblack__] [[__-nowpoint__] [[__-nolabel__]
25 [[__-noaxes__] [[__-full__]
26
27
28 All options can be abbreviated to their shortest unique
29 prefix.
30 !!DESCRIPTION
31
32
33 __ppmcie__ creates a PPM file containing a plot of the
34 CIE ``tongue'' color chart -- to the extent possible in a
35 PPM image. Alternatively, creates a pseudo-PPM image of the
36 color tongue using RGB values from a color system of your
37 choice.
38
39
40 The CIE color tongue is an image of all the hues that can be
41 described by CIE X-Y chromaticity coordinates. They are
42 arranged on a two dimensional coordinate plane with the X
43 chromaticity on the horizontal axis and the Y chro- maticity
44 on the vertical scale. (You can choose alterna- tively to
45 use CIE u'-v' chromaticity coordinates, but the general idea
46 of the color tongue is the same).
47
48
49 Note that the PPM format specifies that the RGB values in
50 the file are from CIE Rec. 709 color system, gamma-cor-
51 rected. And positive. See ppm(5) for details. If you
52 use one of the color system options on __ppmcie__, what
53 you get is not a true PPM image, but is very similar. If you
54 display such __ppmcie__ output using a device that
55 expects PPM input (which includes just about any computer
56 graphics display program), it will display the wrong
57 colors.
58
59
60 However, you may have a device that expects one of these
61 variations on PPM.
62
63
64 In every RGB color system you can specify, including the
65 default (which produces a true PPM image) there are hues in
66 the color tongue that can't be represented. For exam- ple,
67 monochromatic blue-green with a wavelength of 500nm cannot
68 be represented in a PPM image.
69
70
71 For these hues, __ppmcie__ substitutes a similar hue as
72 fol- lows: They are desaturated and rendered as the shade
73 where the edge of the Maxwell triangle intersects a line
74 drawn from the requested shade to the white point defined by
75 the color system's white point. Furthermore, unless you
76 spec- ify the __-full__ option, __ppmcie__ reduces
77 their intensity by 25% compared to the true hues in the
78 image.
79
80
81 __ppmcie__ draws and labels the CIE X-Y coordinate axes
82 unless you choose otherwise with options.
83
84
85 __ppmcie__ draws the Maxwell triangle for the color
86 system in use on the color tongue. The Maxwell triangle is
87 the tri- angle whose vertices are the primary illuminant
88 hues for the color system. The hues inside the triangle show
89 the color gamut for the color system. They are also the only
90 ones that are correct for the CIE X-Y chromaticity coordi-
91 nates shown. (See explanation above).
92
93
94 __ppmcie__ also places a mark at the color system's white
95 point and displays in text the CIE X-Y chromaticities of the
96 primary illuminants and white point for the color sys- tem.
97 You can turn this off with options, though.
98
99
100 __ppmcie__ annotates the periphery of the color tongue
101 with the wavelength, in nanometers of the monochromatic hues
102 which appear there.
103
104
105 Finally, __ppmcie__ displays the black body chromaticity
106 curve for Planckian radiators from 1000 to 30000 kelvins on
107 the image.
108
109
110 You can choose from several standard color systems, or
111 specify one of your own numerically.
112
113
114 CIE charts, by their very nature, contain a very large
115 number of colors. If you're encoding the chart for a col- or
116 mapped device or file format, you'll need to use __pp-
117 mquant__ or __ppmdither__ to reduce the number of
118 colors in the image.
119 !!OPTIONS
120
121
122 __-rec709__|__-cie__|__-ebu__|__-hdtv__|__-ntsc__|__-smpte__
123
124
125 Select a standard color system whose gamut to plot. The
126 default is __-rec709__, which chooses CIE Rec. 709,
127 gamma-corrected. This is the only color system for which
128 __ppmcie__'s output is a true PPM image. See explanation
129 above. __-ebu__ chooses the primaries used in the PAL and
130 SECAM broad- casting standards. __-ntsc__ chooses the
131 primaries specified by the NTSC broadcasting system (few
132 modern monitors actually cover this range). __-smpte__
133 selects the primaries recommended by the Society of Motion
134 Picture and Television Engi- neers (SMPTE) in standards
135 RP-37 and RP-145, and __-hdtv__ uses the much broader
136 ''HDTV ideal'' pri- maries. __-cie__ chooses a color
137 system that has the largest possible gamut within the
138 spectrum of the chart. This is the same color system as you
139 get with the __-cie__ option to John Walker's
140 __cietoppm__ program.
141
142
143 __-xy__
144
145
146 plot CIE 1931 x y chromaticities. This is the
147 default.
148
149
150 __-upvp__
151
152
153 plot u' v' 1976 chromaticities rather than CIE 1931 x y
154 chromaticities. The advantage of u' v' coordinates is that
155 equal intervals of distance on the u' v' plane correspond
156 roughly to the eye's ability to discriminate
157 colors.
158
159
160 __-red__ ''rx ry''
161
162
163 specifies the CIE ''x'' and ''y'' co-ordinates of the
164 red illuminant of a custom color system and se- lects the
165 custom system.
166
167
168 __-green__ ''gx gy''
169
170
171 specifies the CIE ''x'' and ''y'' co-ordinates of the
172 green illuminant of the color system and selects the custom
173 system.
174
175
176 __-blue__ ''bx by''
177
178
179 specifies the CIE ''x'' and ''y'' co-ordinates of the
180 blue illuminant of the color system and selects the custom
181 system.
182
183
184 __-white__ ''wx wy''
185
186
187 specifies the CIE ''x'' and ''y'' co-ordinates of the
188 white point of the color system and selects the custom
189 system.
190
191
192 __-size__ ''edge''
193
194
195 Create a pixmap of ''edge'' by ''edge'' pixels. The
196 de- fault is 512x512.
197
198
199 __-xsize|-width__ ''width''
200
201
202 Sets the width of the generated image to ''width''
203 pixels. The default width is 512 pixels. If the height and
204 width of the image are not the same, the CIE diagram will be
205 stretched in the longer dimension.
206
207
208 __-ysize|-height__ ''height''
209
210
211 Sets the height of the generated image to ''height''
212 pixels. The default height is 512 pixels. If the height and
213 width of the image are not the same, the CIE diagram will be
214 stretched in the longer dimension.
215
216
217 __-noblack__
218
219
220 Don't plot the black body chromaticity curve.
221
222
223 __-nowpoint__
224
225
226 Don't plot the color system's white point.
227
228
229 __-nolabel__
230
231
232 Omit the label.
233
234
235 __-noaxes__
236
237
238 Don't plot axes.
239
240
241 __-full__
242
243
244 Plot the entire CIE tongue in full intensity; don't enhance
245 the gamut of the specified color system.
246 !!SEE ALSO
247
248
249 ppmdither(1), ppmquant(1),
250 ppm(5)
251 !!AUTHOR
252 Copyright (C) 1995 by John Walker
253 (kelvin@fourmilab.ch)
254 WWW home page: http://www.fourmilab.ch/
255 Permission to use, copy, modify, and distribute this
256 soft- ware and its documentation for any purpose and without
257 fee is hereby granted, without any conditions or
258 restrictions. This software is provided ``as is'' without
259 express or im- plied warranty.
260 ----
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