opencv3/C++ 直方图反向投影实例

直方图反向投影：

即取直方图中的值，按直方图面积由大到小，对其对应的像素也由大到小赋予新值。即某种灰度值在图像中所占面积越大，其对应的像素的新值就越大；反之就越小。

示例：

获取测试图像中每个像素的hue数据 hi,j，并找到 hi,j 在hue直方图中的bin的位置

#include<opencv2/opencv.hpp>
using namespace cv;
Mat hue;
int bins = 10;
void histBackprojection(int, void*);
int main()
{
Mat src, hsv;
src = imread("E:/image/image/shape.jpg");
if (src.empty())
{
printf("can not load image \n");
return -1;
}
namedWindow("input", WINDOW_AUTOSIZE);
imshow("input", src);
cvtColor(src, hsv, COLOR_BGR2HSV);
hue.create(hsv.size(), hsv.depth());
int ch[] = {0, 0};
//分离Hue通道:色相通道
mixChannels(&hsv, 1, &hue, 1, ch, 1);
//创建Trackbar来输入bin的数目
createTrackbar("bins:", "input", &bins, 255, histBackprojection);
histBackprojection(0, 0);
waitKey(0);
return 0;
}
void histBackprojection(int, void*)
{
MatND hist, backproj;
int histSize = max(bins, 2);
float range[] = {0, 255};
const float *ranges = {range};
//计算直方图
calcHist(&hue, 1, 0, Mat(), hist,1, &histSize, &ranges, true, false);
//将直方图bin的数值归一化到0-255
normalize(hist, hist, 0, 255, NORM_MINMAX, -1, Mat());
//计算反向投影
calcBackProject(&hue, 1, 0, hist, backproj, &ranges, 1, true);
namedWindow("backprogection", WINDOW_AUTOSIZE);
imshow("backprogection", backproj);
//显示直方图
int binsW = cvRound((double)500/histSize);
Mat histImg = Mat::zeros(500, 500, CV_8UC3);
RNG rng(123);
for (int i = 0; i < bins; i++)
{
Scalar color = Scalar(rng.uniform(0,255),rng.uniform(0,255),rng.uniform(0,255));
rectangle(histImg, Point(i*binsW, 500), Point((i+1)*binsW, 500 - cvRound(hist.at<float>(i) * 500 / 255.0)), color, -1);
}
namedWindow("histogram", WINDOW_AUTOSIZE);
imshow("histogram", histImg);
}