opencv直方图之查表法，均衡化

查表法中的表是一个一维，256的数组，其意思在于对于一个像素点的灰度值进行变换，即如果原像素的灰度值为i，则查表转化后假设负片效果，就是灰度值为255-i。

在画出直方图后，想均衡化，增强对比度的话，可以这样，检测直方图中非零项的最低和最高，将最低设置成0，最高设置成255，其中间则按这种规律转化。

以下为代码：

// opencv_2.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include <opencv245.h>using namespace cv;using namespace std;class Histogram1D{private:int histsize[1];float hranges[2];const float* ranges[1];int channels[1];public:Histogram1D() {histsize[0] = 256 ;hranges[0] = 0.0;hranges[1] = 255.0;ranges[0] = hranges;channels[0] = 0;}Mat getHistogram(const Mat &image);Mat getHistogramImage(const Mat &image);Mat applyLookUp(const Mat &image);Mat stretch(const Mat &image, int minValue);};Mat Histogram1D::getHistogram(const Mat &image){Mat hist;calcHist(&image, 1, channels, Mat(), hist, 1, histsize, ranges);return hist;}Mat Histogram1D::getHistogramImage(const Mat &image){Mat hist = getHistogram(image);double maxVal = 0;double minVal = 0;minMaxLoc(hist, &minVal, &maxVal);Mat histImg(histsize[0],histsize[0],CV_8UC3,Scalar(255,255,255));int hpt = static_cast<int>(0.9*histsize[0]);for (int h = 0; h < histsize[0]; h++){float binVal = hist.at<float>(h);int intensity = static_cast<int>(binVal * hpt / maxVal);line(histImg, Point(h, histsize[0]),          Point(h,histsize[0] - intensity),  Scalar(0,255,0));}return histImg;}//Mat Histogram1D::applyLookUp(const Mat &image)//{//Mat result;//Mat lookup(1, 256, CV_8U);////for (int i = 0; i < 256; i++)//{//lookup.at<uchar>(i) = 255 -i;//}//////LUT(image, lookup, result);//return result;//}Mat Histogram1D::stretch(const Mat &image, int minValue  = 0 ){Mat hist = getHistogram(image);int imin = 0;for (; imin < histsize[0]; imin++){if (hist.at<float>(imin) > minValue ){break;}}int imax = histsize[0] - 1;    for(; imax >=0; imax--){if (hist.at<float>(imax) > minValue){break;}}int dim(256);Mat lookup(1, &dim, CV_8U);for (int i = 0; i < 256; i++){if (i < imin ){lookup.at<uchar>(i) = 0;}else if (i > imax){lookup.at<uchar>(i) = 255;}else{lookup.at<uchar>(i) = static_cast<uchar>(255.0*(i - imin)/(imax - imin) + 0.5);}}Mat result;LUT(image,lookup,result);return result;}int _tmain(int argc, _TCHAR* argv[]){Mat image = imread("C:\\Users\\sony\\Desktop\\pic\\Lena.jpg",0);int sum = 0;int max = 0;Histogram1D h;/*Mat histo = h.getHistogramImage(image);*///for (int i = 0; i < 256; i++)//{//if (histo.at<float>(i) > max)//{//max = histo.at<float>(i);//}///*cout<<"Value"<<i<<"="<<histo.at<float>(i)<<endl;*////*sum += histo.at<float>(i);*/////}//cout<<max<<endl;/*Mat dst = h.applyLookUp(image);*/Mat dst = h.stretch(image);imshow("src",image);imshow("dst", dst);imshow("src H", h.getHistogramImage(image));imshow("dst H", h.getHistogramImage(dst));waitKey(0);return 0;}

效果图如下：

      

                              原图                                                                         处理后