blob: 6630e05c098ddf02e4c2e7dd88c7380a9539e3eb (
plain) (
blame)
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
|
#ifndef _PM_GAMMA_H_
#define _PM_GAMMA_H_
#include <netpbm/pm_config.h>
#include <math.h>
#ifdef __cplusplus
extern "C" {
#endif
#if 0
} /* to fake out automatic code indenters */
#endif
static __inline__ float
pm_gamma709(float const intensity) {
/* Here are parameters of the gamma transfer function
for the Netpbm formats. This is CIE Rec 709.
This transfer function is linear for sample values 0 .. .018
and an exponential for larger sample values.
The exponential is slightly stretched and translated, though,
unlike the popular pure exponential gamma transfer function.
*/
float const gamma = 2.2;
float const oneOverGamma = 1.0 / gamma;
float const linearCutoff = 0.018;
float const linearExpansion =
(1.099 * pow(linearCutoff, oneOverGamma) - 0.099) / linearCutoff;
float brightness;
if (intensity < linearCutoff)
brightness = intensity * linearExpansion;
else
brightness = 1.099 * pow(intensity, oneOverGamma) - 0.099;
return brightness;
}
static __inline__ float
pm_ungamma709(float const brightness) {
/* These are the same parameters as in pm_gamma, above */
float const gamma = 2.2;
float const oneOverGamma = 1.0 / gamma;
float const linearCutoff = 0.018;
float const linearExpansion =
(1.099 * pow(linearCutoff, oneOverGamma) - 0.099) / linearCutoff;
float intensity;
if (brightness < linearCutoff * linearExpansion)
intensity = brightness / linearExpansion;
else
intensity = pow((brightness + 0.099) / 1.099, gamma);
return intensity;
}
#ifdef __cplusplus
}
#endif
#endif
|
