直方图反向投影(Histogram Back Projection)
1、反向投影;
2、操作步骤与API;
3、代码演示;
直方图反向投影
1、反向投影是反映直方图模型在目标图像中的分布情况,即用直方图模型去目标图像中寻找是否有相似的对象,实现对特定对象的检测,通常用HSV色彩空间的HS(hue,saturation)两个通道直方图模型;
直方图反向投影步骤
1、建立直方图模型;
2、计算待测图像直方图并映射到这个模型中;
3、从模型反向计算生成图像;
实现步骤与API
1、反向投影API : calcBackProject
;
2、操作步骤:
①加载图片;
②将图像从RGB色彩空间转换到HSV色彩空间;
③计算直方图并归一化(calcHist()、normalize());
④计算反向投影图像(calcBackProject() );
Code
#include <opencv2/opencv.hpp>
#include <iostream>
using namespace std;
using namespace cv;
Mat src, hsv, hue;
int bins = 12;
void Hist_And_Backprojection(int, void*);
int main(int argc, char** argv)
{
src = imread("C:\\Users\\hello\\Desktop\\37.jpg");
if (!src.data)
{
cout << "could not load the image..." << endl;
return -1;
}
namedWindow("input image", WINDOW_AUTOSIZE);
namedWindow("Histogram image", WINDOW_AUTOSIZE);
imshow("input image", src);
//色彩空间转换
cvtColor(src, hsv, CV_BGR2HSV);
hue.create(hsv.size(), hsv.depth());
int nchannels[] = {
0,0 };
mixChannels(&hsv, 1, &hue, 1,nchannels,1);
//计算hue的直方图 1维 hue:0-180, saturation:0-256;
createTrackbar("Histogram Bins:", "input image", &bins, 180, Hist_And_Backprojection);
Hist_And_Backprojection(0, 0);
waitKey(0);
return 0;
}
void Hist_And_Backprojection(int, void*)
{
//计算直方图并归一化
float range[] = {
0,180 };
const float *histRanges = {
range };
Mat h_hist;
calcHist(&hue, 1, 0, Mat(), h_hist,1, &bins, &histRanges, true, false);
normalize(h_hist, h_hist, 0, 255, NORM_MINMAX, -1, Mat()); //alpha beta为归一化值的范围 归一化到0到255之间
Mat backPrjImage;
calcBackProject(&hue, 1, 0, h_hist, backPrjImage, &histRanges, 1, true);
imshow("BackProj", backPrjImage);
//绘制直方图
int hist_h = 400;
int hist_w = 400;
Mat histImage(hist_w, hist_h, CV_8UC3, Scalar(0, 0, 0));
int bin_w = hist_w / bins;
for (int i = 1; i < bins; i++)
{
//-1表示填充矩形
rectangle(histImage,
Point((i - 1)*bin_w, cvRound(hist_h - h_hist.at<float>(i - 1) * (400 / 255))),
//Point((i)*bin_w, cvRound(hist_h - h_hist.at<float>(i) * (400 / 255))),
Point((i)*bin_w, cvRound(hist_h)),
Scalar(0, 0, 255), -1);
}
imshow("Histogram image", histImage);
return;
}