3.4 Gamma校正+对数Log变换

Gamma校正是对输入图像灰度值进行的非线性操作,使输出图像灰度值与输入图像灰度值呈指数关系:

A是一个常数,通常取1,这个指数即为Gamma。

Gamma校正的原理很简单,就一个很简单的表达式,如下图所示:

其中V_in的取值范围是0~1,最重要的参数就是公式中的γ参数!

γ的值决定了输入图像和输出图像之间的灰度映射方式,即决定了是增强低灰度值区域还是增高灰度值区域。
γ>1时,图像的高灰度区域对比度得到增强。
γ<1时,图像的低灰度区域对比度得到增强。
γ=1时,不改变原图像。

伽马变换对于图像对比度偏低,并且整体亮度值偏高(对于于相机过曝)情况下的图像增强效果明显。

 1 #include <opencv2/highgui/highgui.hpp>    
 2 #include <opencv2/imgproc/imgproc.hpp>
 3 
 4 using namespace cv;
 5 
 6 int main(int argc, char *argv[])
 7 {
 8     Mat image = imread("D:\\Gamma校正.jpg");
 9     Mat imageGamma(image.size(), CV_32FC3);
10     for (int i = 0; i < image.rows; i++)
11     {
12         for (int j = 0; j < image.cols; j++)
13         {
14             imageGamma.at<Vec3f>(i, j)[0] = (image.at<Vec3b>(i, j)[0])*(image.at<Vec3b>(i, j)[0])*(image.at<Vec3b>(i, j)[0]);
15             imageGamma.at<Vec3f>(i, j)[1] = (image.at<Vec3b>(i, j)[1])*(image.at<Vec3b>(i, j)[1])*(image.at<Vec3b>(i, j)[1]);
16             imageGamma.at<Vec3f>(i, j)[2] = (image.at<Vec3b>(i, j)[2])*(image.at<Vec3b>(i, j)[2])*(image.at<Vec3b>(i, j)[2]);
17         }
18     }
19     //归一化到0~255  
20     normalize(imageGamma, imageGamma, 0, 255, CV_MINMAX);
21     //转换成8bit图像显示  
22     convertScaleAbs(imageGamma, imageGamma);
23     imshow("原图", image);
24     imshow("伽马变换图像增强效果", imageGamma);
25     waitKey();
26     return 0;
27 }
View Code

 

 1 //////朱伟opencv图像处理编程实例
 2 #include <iostream>  
 3 #include <opencv2\core\core.hpp>  
 4 #include <opencv2\highgui\highgui.hpp>  
 5 #include <opencv2\imgproc\imgproc.hpp>  
 6 #include<cmath>
 7 using namespace cv;
 8 
 9 Mat gammaTransform(Mat &srcImage, float kFactor)
10 {
11 
12     unsigned char LUT[256];
13     for (int i = 0; i < 256; i++)
14     {
15         float f = (i + 0.5f) / 255;
16         f = (float)(pow(f, kFactor));
17         LUT[i] = saturate_cast<uchar>(f*255.0f - 0.5f);
18     }
19     Mat resultImage = srcImage.clone();
20 
21     if (srcImage.channels() == 1)
22     {
23 
24         MatIterator_<uchar> iterator = resultImage.begin<uchar>();
25         MatIterator_<uchar> iteratorEnd = resultImage.end<uchar>();
26         for (; iterator != iteratorEnd; iterator++)
27         {
28             *iterator = LUT[(*iterator)];
29         }
30     }
31     else
32     {
33 
34 
35         MatIterator_<Vec3b> iterator = resultImage.begin<Vec3b>();
36         MatIterator_<Vec3b> iteratorEnd = resultImage.end<Vec3b>();
37         for (; iterator != iteratorEnd; iterator++)
38         {
39             (*iterator)[0] = LUT[((*iterator)[0])];//b
40             (*iterator)[1] = LUT[((*iterator)[1])];//g
41             (*iterator)[2] = LUT[((*iterator)[2])];//r
42         }
43     }
44     return resultImage;
45 }
46 int main()
47 {
48     Mat srcImage = imread("D:\\小女孩与熊.jpg");
49     if (!srcImage.data)
50     {
51         printf("could not load image...\n");
52         return -1;
53     }
54     //取两种不同的gamma值
55     float gamma1 = 3.33f;
56     float gamma2 = 0.33f;
57     float kFactor1 = 1 / gamma1;
58     float kFactor2 = 1 / gamma2;
59     Mat result1 = gammaTransform(srcImage, kFactor1);
60     Mat result2 = gammaTransform(srcImage, kFactor2);
61     imshow("srcImage", srcImage);
62     imshow("res1", result1);
63     imshow("res2", result2);
64     waitKey(0);
65     return 0;
66 }
View Code

 

对数Log变换:

对数变换对于整体对比度偏低并且灰度值偏低的图像增强效果较好。

 1 /////////////////////////////////////对数Log变换////////////////////////////////////////
 2 ////https://blog.csdn.net/dcrmg/article/details/53677739
 3 #include <opencv2/highgui/highgui.hpp>    
 4 #include <opencv2/imgproc/imgproc.hpp>
 5 
 6 using namespace cv;
 7 
 8 int main(int argc, char *argv[])
 9 {
10     Mat image = imread("D:\\对数Log变换.jpg");
11     Mat imageLog(image.size(), CV_32FC3);
12     for (int i = 0; i < image.rows; i++)
13     {
14         for (int j = 0; j < image.cols; j++)
15         {
16             imageLog.at<Vec3f>(i, j)[0] = log(1 + image.at<Vec3b>(i, j)[0]);
17             imageLog.at<Vec3f>(i, j)[1] = log(1 + image.at<Vec3b>(i, j)[1]);
18             imageLog.at<Vec3f>(i, j)[2] = log(1 + image.at<Vec3b>(i, j)[2]);
19         }
20     }
21     //归一化到0~255  
22     normalize(imageLog, imageLog, 0, 255, CV_MINMAX);
23     //转换成8bit图像显示  
24     convertScaleAbs(imageLog, imageLog);
25     imshow("Soure", image);
26     imshow("after", imageLog);
27     waitKey();
28     return 0;
29 }
View Code

参考链接:

https://blog.csdn.net/linqianbi/article/details/78617615

https://blog.csdn.net/dcrmg/article/details/53677739

https://blog.csdn.net/lxy201700/article/details/24929013

其他:

https://www.cnblogs.com/qiqibaby/p/5325193.html 

https://www.cnblogs.com/lcchuguo/p/4052077.html 

posted @ 2018-08-16 19:36  BreakofDawn  阅读(2096)  评论(0编辑  收藏  举报