opencv4入门笔记（37）：直方图反向投影萤火

本系列代码托管于：https://github.com/chintsan-code/opencv4-tutorials

本篇使用的项目为：back_project

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, const char** argv) {
	Mat model = imread("../sample/sample.png");
	Mat src = imread("../sample/target.png");
	if (src.empty() || model.empty()) {
		printf("could not find image files");
		return -1;
	}
	namedWindow("input", WINDOW_AUTOSIZE);
	imshow("input", src);
	imshow("sample", model);

	Mat model_hsv, image_hsv;
	cvtColor(model, model_hsv, COLOR_BGR2HSV);
	cvtColor(src, image_hsv, COLOR_BGR2HSV);

	int h_bins = 48, s_bins = 48;
	int histSize[] = { h_bins, s_bins };
	int channels[] = { 0, 1 };
	Mat roiHist;
	float h_range[] = { 0, 180 };
	float s_range[] = { 0, 255 };
	const float* ranges[] = { h_range, s_range };
	calcHist(&model_hsv, 1, channels, Mat(), roiHist, 2, histSize, ranges, true, false);
	normalize(roiHist, roiHist, 0, 255, NORM_MINMAX, -1, Mat());
	MatND backproj;
	calcBackProject(&image_hsv, 1, channels, roiHist, backproj, ranges, 1.0);
	imshow("back projection demo", backproj);

	waitKey(0);
	destroyAllWindows();
	return 0;
}

反向投影是一种记录给定图像中的像素点如何适应直方图模型像素分布的方式，简单来讲，反向投影就是首先计算某一特征的直方图模型，然后使用模型去寻找图像中存在的特征。反向投影在某一位置的值就是原图对应位置像素值在原图像中的总数目。可以用于目标检测。

calcBackProject：计算直方图的反向投影

void calcBackProject( const Mat* images, int nimages, const int* channels, InputArray hist, OutputArray backProject, const float** ranges, double scale = 1, bool uniform = true );