亮度对比度调整
（一）算法
亮度对比度调整的算法，我在网上找了很多篇，个人觉得以下这个算法效果较好，比较接近Photoshop的效果。
Algorithm of Brightness Contrast transformation
The formula is:
y = [x - 127.5 * (1 - B)] * k + 127.5 * (1 + B);
The formula is:
y = [x - 127.5 * (1 - B)] * k + 127.5 * (1 + B);
x is the input pixel value
y is the output pixel value
B is brightness, value range is [-1,1]
k is used to adjust contrast
k = tan( (45 + 44 * c) / 180 * PI );
c is contrast, value range is [-1,1]
于是，用OpenCV C++编写了一个 adjustBrightnessContrast()函数，可同时调整亮度、对比度。
（二）源码及例程
例程如下， 其中包含 adjustBrightnessContrast()函数。
1 #include <iostream>
2 #include "opencv2/core.hpp"
3 #include "opencv2/imgproc.hpp"
4 #include "opencv2/highgui.hpp"
5
6 using namespace std;
7 using namespace cv;
8
9
10 #define SWAP(a, b, t) do { t = a; a = b; b = t; } while(0)
11 #define CLIP_RANGE(value, min, max) ( (value) > (max) ? (max) : (((value) < (min)) ? (min) : (value)) )
12 #define COLOR_RANGE(value) CLIP_RANGE(value, 0, 255)
13
14 /**
15 * Adjust Brightness and Contrast
16 *
17 * @param src [in] InputArray
18 * @param dst [out] OutputArray
19 * @param brightness [in] integer, value range [-255, 255]
20 * @param contrast [in] integer, value range [-255, 255]
21 *
22 * @return 0 if success, else return error code
23 */
24 int adjustBrightnessContrast(InputArray src, OutputArray dst, int brightness, int contrast)
25 {
26 Mat input = src.getMat();
27 if( input.empty() ) {
28 return -1;
29 }
30
31 dst.create(src.size(), src.type());
32 Mat output = dst.getMat();
33
34 brightness = CLIP_RANGE(brightness, -255, 255);
35 contrast = CLIP_RANGE(contrast, -255, 255);
36
37 /**
38 Algorithm of Brightness Contrast transformation
39 The formula is:
40 y = [x - 127.5 * (1 - B)] * k + 127.5 * (1 + B);
41 x is the input pixel value
42 y is the output pixel value
43 B is brightness, value range is [-1,1]
44 k is used to adjust contrast
45 k = tan( (45 + 44 * c) / 180 * PI );
46 c is contrast, value range is [-1,1]
47 */
48
49 double B = brightness / 255.;
50 double c = contrast / 255. ;
51 double k = tan( (45 + 44 * c) / 180 * M_PI );
52
53 Mat lookupTable(1, 256, CV_8U);
54 uchar *p = lookupTable.data;
55 for (int i = 0; i < 256; i++)
56 p[i] = COLOR_RANGE( (i - 127.5 * (1 - B)) * k + 127.5 * (1 + B) );
57
58 LUT(input, lookupTable, output);
59
60 return 0;
61 }
62
63
64 //=====主程序开始====
65
66 static string window_name = "photo";
67 static Mat src;
68 static int brightness = 255;
69 static int contrast = 255;
70
71 static void callbackAdjust(int , void *)
72 {
73 Mat dst;
74 adjustBrightnessContrast(src, dst, brightness - 255, contrast - 255);
75 imshow(window_name, dst);
76 }
77
78
79 int main()
80 {
81 src = imread("building.jpg");
82
83 if ( !src.data ) {
84 cout << "error read image" << endl;
85 return -1;
86 }
87
88 namedWindow(window_name);
89 createTrackbar("brightness", window_name, &brightness, 2*brightness, callbackAdjust);
90 createTrackbar("contrast", window_name, &contrast, 2*contrast, callbackAdjust);
91 callbackAdjust(0, 0);
92
93 waitKey();
94
95 return 0;
96
运行效果：
原图：
调整参数， 实施亮度对比度调整后：
