1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
|
/*
* cam97s3
*
* Color Appearance Model, based on
* CIECAM97, "Revision for Practical Applications"
* by Mark D. Fairchild, with the addition of the Viewing Flare
* model described on page 487 of "Digital Color Management",
* by Edward Giorgianni and Thomas Madden, and the
* Helmholtz-Kohlraush effect, using the equation
* the Bradford-Hunt 96C model as detailed in Mark Fairchilds
* book "Color Appearance Models".
*
* Author: Graeme W. Gill
* Date: 5/10/00
* Version: 1.20
*
* Copyright 2000 Graeme W. Gill
* Please refer to COPYRIGHT file for details.
* This material is licenced under the GNU AFFERO GENERAL PUBLIC LICENSE Version 3 :-
* see the License.txt file for licencing details.
*/
/* Algorithm tweaks */
#define CIECAM97S3_SPLINE_E /* Use spline interpolation for eccentricity factor */
/* Definitions assumed here:
Stimulus field is the 2 degrees field of view of the sample
being characterised.
Viewing/Scene/Image field is the area of the whole image or
display surface that the stimulus is part of.
Background field is 10-12 degree field surrounding the stimulus field.
This may be within, overlap or encompass the Viewing/Scene/Image field.
Surround/Adapting field is the visual field minus the background field.
Visual field is the 130 degree angular field that is seen by the eyes.
Illuminating field is the field that illuminates the reflective
Scene/Image. It may be the same as the Ambient field.
Ambient field is the whole surrounding environmental light field.
NOTE: In "Digital Color Management", Giorgianni and Madden use the term
"Surround" to mean the same thing as "Background" in the CIECAM97 terminology.
The ICC standard doesn't define what it means by "Surround illumination".
*/
/* Rules of Thumb: */
/* Ambient Luminance (Lat, cd/m^2) is Ambient Illuminance (Lux) divided by PI. */
/* i.e. Lat = Iat/PI */ /* (1 foot candle = 0.0929 lux) */
/* The Adapting/Surround Luminance is often taken to be */
/* the 20% of the Ambient Luminance. (gray world) */
/* i.e. La = Lat/5 = Iat/15.7 */
/* For a reflective print, the Viewing/Scene/Image luminance (Lv, cd/m^2), */
/* will be the Illuminating Luminance (Li, cd/m^2) reflected by the */
/* media white point (Yw) */
/* If there is no special illumination for a reflective print, */
/* then the Illuminating Luminance (Li) will be the Ambient Luminance (Lat) */
/* An emisive display will have an independently determined Lv. */
/* The classification of the type of surround is */
/* determined by comparing the Adapting/Surround luminance (La, cd/m^2) */
/* with the average luminance of the Viewing/Scene/Image field (Lv, cd/m^2) */
/* La/Lv == 0%, dark */
/* La/Lv 0 - 20%, dim */
/* La/Lv > 20%, average */
/* special, cut sheet */
/* The Background relative luminance Yb is typically assumed to */
/* be 0.18 .. 0.2, and is assumed to be grey. */
/* The source of flare light depends on the type of display system. */
/* For a CRT, it will be the Ambient light reflecting off the glass surface. */
/* (This implies Yf = Lat * reflectance/Lv) */
/* For a reflection print, it will be the Illuminant reflecting from the media */
/* surface. (Yf = Li * reflectance) */
/* For a projected image, it will be stray projector light, scattered by the */
/* surround, screen and air particles. (Yf = Li * reflectance_and_scattering) */
/*
Typical Ambient Illuminance brightness
(Lux) La Condition
11 1 Twilight
32 2 Subdued indoor lighting
64 4 Less than typical office light; sometimes recommended for
display-only workplaces (sRGB)
350 22 Typical Office (sRGB annex D)
500 32 Practical print evaluationa (ISO-3664 P2)
1000 64 Good Print evaluation (CIE 116-1995)
1000 64 Overcast Outdoors
2000 127 Critical print evaluation (ISO-3664 P1)
10000 637 Typical outdoors, full daylight
50000 3185 Bright summers day
*/
/* ---------------------------------- */
struct _cam97s3 {
/* Public: */
void (*del)(struct _cam97s3 *s); /* We're done with it */
int (*set_view)(
struct _cam97s3 *s,
ViewingCondition Ev, /* Enumerated Viewing Condition */
double Wxyz[3], /* Reference/Adapted White XYZ (Y scale 1.0) */
double La, /* Adapting/Surround Luminance cd/m^2 */
double Yb, /* Luminance of Background relative to reference white (range 0.0 .. 1.0) */
double Lv, /* Luminance of white in the Viewing/Scene/Image field (cd/m^2) */
/* Ignored if Ev is set */
double Yf, /* Flare as a fraction of the reference white (range 0.0 .. 1.0) */
double Fxyz[3], /* The Flare white coordinates (typically the Ambient color) */
int hk /* Flag, NZ to use Helmholtz-Kohlraush effect */
);
/* Conversions */
int (*XYZ_to_cam)(struct _cam97s3 *s, double *out, double *in);
int (*cam_to_XYZ)(struct _cam97s3 *s, double *out, double *in);
/* Private: */
/* Scene parameters */
ViewingCondition Ev; /* Enumerated Viewing Condition */
double Wxyz[3]; /* Reference/Adapted White XYZ (Y range 0.0 .. 1.0) */
double Yb; /* Relative Luminance of Background to reference white (Y range 0.0 .. 1.0) */
double La; /* Adapting/Surround Luminance cd/m^2 */
double Yf; /* Flare as a fraction of the reference white (Y range 0.0 .. 1.0) */
double Fxyz[3]; /* The Flare white coordinates (typically the Ambient color) */
/* Internal parameters */
double C; /* Surround Impact */
double Nc; /* Chromatic Induction */
double F; /* Adaptation Degree */
/* Pre-computed values */
double Fsc; /* Flare scale */
double Fisc; /* Inverse flare scale */
double Fsxyz[3]; /* Scaled Flare color coordinates */
double rgbW[3]; /* Sharpened cone response white values */
double D; /* Degree of chromatic adaption */
double rgbcW[3]; /* Chromatically transformed white value */
double rgbpW[3]; /* Hunt-Pointer-Estevez cone response space white */
double n; /* Background induction factor */
double nn; /* Precomuted function of n */
double Fl; /* Lightness contrast factor ?? */
double Nbb; /* Background brightness induction factors */
double Ncb; /* Chromatic brightness induction factors */
double z; /* Base exponential nonlinearity */
double rgbaW[3]; /* Post-adapted cone response of white */
double Aw; /* Achromatic response of white */
/* Flags */
int hk; /* If NZ, use Helmholtz-Kohlraush effect */
int trace; /* Trace values through computation */
}; typedef struct _cam97s3 cam97s3;
/* Create a cam97s3 conversion class, with default viewing conditions */
cam97s3 *new_cam97s3(void);
|
