OpenCV 自动对比度和色阶增强

实现函数代码：

 1 /****************************************/
 2 /*   实现自动对比度的函数                  */
 3 /*   目前只有前后中通道调用                */
 4 /*   彩色的已经加入到了函数内部             */
 5 /*****************************************/
 6 void BrightnessAndContrastAuto(const cv::Mat &src, cv::Mat &dst, float clipHistPercent)
 7 {
 8     CV_Assert(clipHistPercent >= 0);
 9     CV_Assert((src.type() == CV_8UC1) || (src.type() == CV_8UC3) || (src.type() == CV_8UC4));
10 
11     int histSize = 256;
12     float alpha, beta;
13     double minGray = 0, maxGray = 0;
14 
15     //to calculate grayscale histogram
16     cv::Mat gray;
17     if (src.type() == CV_8UC1) gray = src;
18     else if (src.type() == CV_8UC3) cvtColor(src, gray, CV_BGR2GRAY);
19     else if (src.type() == CV_8UC4) cvtColor(src, gray, CV_BGRA2GRAY);
20     if (clipHistPercent == 0)
21     {
22         // keep full available range
23         cv::minMaxLoc(gray, &minGray, &maxGray);
24     }
25     else
26     {
27         cv::Mat hist; //the grayscale histogram
28 
29         float range[] = { 0, 256 };
30         const float* histRange = { range };
31         bool uniform = true;
32         bool accumulate = false;
33         cv::calcHist(&gray, 1, 0, cv::Mat (), hist, 1, &histSize, &histRange, uniform, accumulate);
34 
35         // calculate cumulative distribution from the histogram
36         std::vector<float> accumulator(histSize);
37         accumulator[0] = hist.at<float>(0);
38         for (int i = 1; i < histSize; i++)
39         {
40             accumulator[i] = accumulator[i - 1] + hist.at<float>(i);
41         }
42 
43         // locate points that cuts at required value
44         float max = accumulator.back();
45         clipHistPercent *= (max / 100.0); //make percent as absolute
46         clipHistPercent /= 2.0; // left and right wings
47         // locate left cut
48         minGray = 0;
49         while (accumulator[minGray] < clipHistPercent)
50             minGray++;
51 
52         // locate right cut
53         maxGray = histSize - 1;
54         while (accumulator[maxGray] >= (max - clipHistPercent))
55             maxGray--;
56     }
57 
58     // current range
59     float inputRange = maxGray - minGray;
60 
61     alpha = (histSize - 1) / inputRange;   // alpha expands current range to histsize range
62     beta = -minGray * alpha;             // beta shifts current range so that minGray will go to 0
63 
64     // Apply brightness and contrast normalization
65     // convertTo operates with saurate_cast
66     src.convertTo(dst, -1, alpha, beta);
67 
68     // restore alpha channel from source 
69     if (dst.type() == CV_8UC4)
70     {
71         int from_to[] = { 3, 3};
72         cv::mixChannels(&src, 4, &dst,1, from_to, 1);
73     }
74     return;
75 }