blob: 6c597093ddf8fafc3de3dbac41cdd65c1666bc20 (
plain)
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
|
/* SPDX-License-Identifier: BSD-2-Clause */
/*
* Copyright (C) 2024, Ideas on Board Oy
*
* libipa miscellaneous colour helpers
*/
#include "colours.h"
#include <algorithm>
#include <cmath>
namespace libcamera {
namespace ipa {
/**
* \file colours.h
* \brief Functions to reduce code duplication between IPA modules
*/
/**
* \brief Estimate luminance from RGB values following ITU-R BT.601
* \param[in] rgb The RGB value
*
* This function estimates a luminance value from a triplet of Red, Green and
* Blue values, following the formula defined by ITU-R Recommendation BT.601-7
* which can be found at https://www.itu.int/rec/R-REC-BT.601
*
* \return The estimated luminance value
*/
double rec601LuminanceFromRGB(const RGB<double> &rgb)
{
return (rgb.r() * .299) + (rgb.g() * .587) + (rgb.b() * .114);
}
/**
* \brief Estimate correlated colour temperature from RGB color space input
* \param[in] rgb The RGB value
*
* This function estimates the correlated color temperature RGB color space
* input. In physics and color science, the Planckian locus or black body locus
* is the path or locus that the color of an incandescent black body would take
* in a particular chromaticity space as the black body temperature changes.
*
* If a narrow range of color temperatures is considered (those encapsulating
* daylight being the most practical case) one can approximate the Planckian
* locus in order to calculate the CCT in terms of chromaticity coordinates.
*
* More detailed information can be found in:
* https://en.wikipedia.org/wiki/Color_temperature#Approximation
*
* \return The estimated color temperature
*/
uint32_t estimateCCT(const RGB<double> &rgb)
{
/* Convert the RGB values to CIE tristimulus values (XYZ) */
double X = (-0.14282) * rgb.r() + (1.54924) * rgb.g() + (-0.95641) * rgb.b();
double Y = (-0.32466) * rgb.r() + (1.57837) * rgb.g() + (-0.73191) * rgb.b();
double Z = (-0.68202) * rgb.r() + (0.77073) * rgb.g() + (0.56332) * rgb.b();
/* Calculate the normalized chromaticity values */
double x = X / (X + Y + Z);
double y = Y / (X + Y + Z);
/* Calculate CCT */
double n = (x - 0.3320) / (0.1858 - y);
return 449 * n * n * n + 3525 * n * n + 6823.3 * n + 5520.33;
}
} /* namespace ipa */
} /* namespace libcamera */
|
