OpenCV中直方圖的計算和繪制

主要記錄一下幾個關鍵的API:

cvRound(輸入一個浮點數 );//返回一個整型數，取整的方法為四舍五入 split(輸入多通道圖像，數組或者vector變量。 );

計算直方圖

calcHist(&分割后的單通道圖像，輸入數組的個數，需要統計的通道索引，Mat()掩碼儲存直方圖的矩陣，直方圖的維數，&每個維度的bin數，&每個維度的取值范圍，true，false );

歸一化，將直方圖bin中的值縮放到指定的范圍:

normalize(輸入數組，歸一化后的輸出數組，歸一化范圍的小值，歸一化范圍的大值，NORM_MINMAX歸一化方法，-1，指示歸一化后的輸出數組與輸入數組同類型，Mat()掩碼 );

下面你是一個手敲的demo:

#include "opencv2/opencv.hpp" #include <vector>using namespace std; using namespace cv;int main(){Mat src = imread("/home/dynamicw/Project/C++_Project/opencvtest/src/lesson01/source/grass.jpg");imshow("src",src);vector<Mat> planes;split(src,planes);imshow("b",planes.at(0));imshow("g",planes.at(1));imshow("r",planes.at(2));int histSize = 255;float range[] = {0,255};const float* histRange = {range};Mat r_hist,g_hist,b_hist;calcHist(&planes[0],1,0,Mat(),r_hist,1,&histSize,&histRange,true,false);calcHist(&planes[1],1,0,Mat(),g_hist,1,&histSize,&histRange,true,false);calcHist(&planes[2],1,0,Mat(),b_hist,1,&histSize,&histRange,true,false);Mat histImage(400,400,CV_8UC3,Scalar(0,0,0));normalize(r_hist,r_hist,0,400,NORM_MINMAX,-1,Mat());normalize(g_hist,g_hist,0,400,NORM_MINMAX,-1,Mat());normalize(b_hist,b_hist,0,400,NORM_MINMAX,-1,Mat());int bin_w = cvRound((double)400/histSize);for(int i = 1;i < histSize;i++){line(histImage,Point(bin_w*(i-1),400-cvRound(r_hist.at<float>(i-1))),Point(bin_w*(i),cvRound(400-r_hist.at<float>(i))),Scalar(0,0,255),2,8);line(histImage,Point(bin_w*(i-1),400-cvRound(g_hist.at<float>(i-1))),Point(bin_w*(i),cvRound(400-g_hist.at<float>(i))),Scalar(0,255,0),2,8);line(histImage,Point(bin_w*(i-1),400-cvRound(b_hist.at<float>(i-1))),Point(bin_w*(i),cvRound(400-b_hist.at<float>(i))),Scalar(255,0,0),2,8);}imshow("hist",histImage);waitKey(0);return 0; }

總結

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