OpenCV案例(五)： 更换背景色

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1、证件背景替换

代码实现思路：

    1.将二维图像数据线性化

    2.使用K-means聚类；分离出背景色

    3.背景与人物像素二值化

    4.腐蚀 + 高斯模糊：图像与背景交汇处高斯模糊化

    5.更换背景色以及交汇处融合处理

代码：

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

using namespace std;
using namespace cv;

int main(int argc, char** argv) {
	Mat src = imread("../img/toux.jpg");
	if (src.empty()) {
		printf("could not load image...\n");
		return -1;
	}
	imshow("原图", src);

	// 1.将二维图像数据线性化
	Mat data;
	for (int i = 0; i < src.rows; i++)     //像素点线性排列
		for (int j = 0; j < src.cols; j++)
		{
			Vec3b point = src.at<Vec3b>(i, j);
			Mat tmp = (Mat_<float>(1, 3) << point[0], point[1], point[2]);
			data.push_back(tmp);
		}

	// 2.使用K-means聚类；分离出背景色
	int numCluster = 4;
	Mat labels;
	TermCriteria criteria = TermCriteria(TermCriteria::EPS + TermCriteria::COUNT, 10, 0.1);
	kmeans(data, numCluster, labels, criteria, 3, KMEANS_PP_CENTERS);

	// 3.背景与人物二值化
	Mat mask = Mat::zeros(src.size(), CV_8UC1);
	int index = src.rows * 2 + 2;  //获取点（2，2）作为背景色
	int cindex = labels.at<int>(index);
	/*  提取背景特征 */
	for (int row = 0; row < src.rows; row++) {
		for (int col = 0; col < src.cols; col++) {
			index = row * src.cols + col;
			int label = labels.at<int>(index);
			if (label == cindex) { // 背景
				mask.at<uchar>(row, col) = 0;
			}
			else {
				mask.at<uchar>(row, col) = 255;
			}
		}
	}
	//imshow("mask", mask);

	// 4.腐蚀 + 高斯模糊：图像与背景交汇处高斯模糊化
	Mat k = getStructuringElement(MORPH_RECT, Size(3, 3), Point(-1, -1));
	erode(mask, mask, k);
	//imshow("erode-mask", mask);
	GaussianBlur(mask, mask, Size(3, 3), 0, 0);
	//imshow("Blur Mask", mask);

	// 5.更换背景色以及交汇处融合处理
	RNG rng(12345);
	Vec3b color;  //设置的背景色
	color[0] = 217;//rng.uniform(0, 255);
	color[1] = 60;// rng.uniform(0, 255);
	color[2] = 160;// rng.uniform(0, 255);
	Mat result(src.size(), src.type());

	double w = 0.0;   //融合权重
	int b = 0, g = 0, r = 0;
	int b1 = 0, g1 = 0, r1 = 0;
	int b2 = 0, g2 = 0, r2 = 0;

	for (int row = 0; row < src.rows; row++) {
		for (int col = 0; col < src.cols; col++) {
			int m = mask.at<uchar>(row, col);
			if (m == 255) {
				result.at<Vec3b>(row, col) = src.at<Vec3b>(row, col); // 前景
			}
			else if (m == 0) {
				result.at<Vec3b>(row, col) = color; // 背景
			}
			else {/* 融合处理部分 */
				w = m / 255.0;
				b1 = src.at<Vec3b>(row, col)[0];
				g1 = src.at<Vec3b>(row, col)[1];
				r1 = src.at<Vec3b>(row, col)[2];

				b2 = color[0];
				g2 = color[1];
				r2 = color[2];

				b = b1 * w + b2 * (1.0 - w);
				g = g1 * w + g2 * (1.0 - w);
				r = r1 * w + r2 * (1.0 - w);

				result.at<Vec3b>(row, col)[0] = b;
				result.at<Vec3b>(row, col)[1] = g;
				result.at<Vec3b>(row, col)[2] = r;
			}
		}
	}
	imshow("背景替换", result);

	waitKey(0);
	return 0;
}

结果：

 

2、视频背景替换

视频背景替换思路：

• Take each frame of the video
• Convert from BGR to HSV color-space
• We threshold the HSV image for a range of blue color
• Now extract the blue object alone, we can do whatever on that image we want.

视频帧背景替换关键API:

     1、   cvtColor(frame, hsv, COLOR_BGR2HSV);  //转换颜色域
     2、   inRange(hsv, Scalar(35, 43, 46), Scalar(155, 255, 255), OutImg);  //提取背景

代码：

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

using namespace cv;
using namespace std;

Mat replace_and_blend(Mat &frame, Mat &mask);
Mat background_01;
Mat background_02;
int main(int argc, char** argv) {
	// start here...	
	background_01 = imread("D:/vcprojects/images/bg_01.jpg");
	background_02 = imread("D:/vcprojects/images/bg_02.jpg");
	VideoCapture capture;
	capture.open("D:/vcprojects/images/01.mp4");
	if (!capture.isOpened()) {
		printf("could not find the video file...\n");
		return -1;
	}
	char* title = "input video";
	char* resultWin = "result video";
	namedWindow(title, CV_WINDOW_AUTOSIZE);
	namedWindow(resultWin, CV_WINDOW_AUTOSIZE);
	Mat frame, hsv, mask;
	int count = 0;
	while (capture.read(frame)) {
		cvtColor(frame, hsv, COLOR_BGR2HSV);
		inRange(hsv, Scalar(35, 43, 46), Scalar(155, 255, 255), mask);
		// 形态学操作
		Mat k = getStructuringElement(MORPH_RECT, Size(3, 3), Point(-1, -1));
		morphologyEx(mask, mask, MORPH_CLOSE, k);
		erode(mask, mask, k);
		GaussianBlur(mask, mask, Size(3, 3), 0, 0);

		Mat result = replace_and_blend(frame, mask);
		char c = waitKey(1);
		if (c == 27) {
			break;
		}
		imshow(resultWin, result);
		imshow(title, frame);
	}

	waitKey(0);
	return 0;
}

Mat replace_and_blend(Mat &frame, Mat &mask) {
	Mat result = Mat::zeros(frame.size(), frame.type());
	int h = frame.rows;
	int w = frame.cols;
	int dims = frame.channels();

	// replace and blend
	int m = 0;
	double wt = 0;

	int r = 0, g = 0, b = 0;
	int r1 = 0, g1 = 0, b1 = 0;
	int r2 = 0, g2 = 0, b2 = 0;

	for (int row = 0; row < h; row++) {
		uchar* current = frame.ptr<uchar>(row);
		uchar* bgrow = background_02.ptr<uchar>(row);
		uchar* maskrow = mask.ptr<uchar>(row);
		uchar* targetrow = result.ptr<uchar>(row);
		for (int col = 0; col < w; col++) {
			m = *maskrow++;
			if (m == 255) { // 背景
				*targetrow++ = *bgrow++;
				*targetrow++ = *bgrow++;
				*targetrow++ = *bgrow++;
				current += 3;

			} else if(m==0) {// 前景
				*targetrow++ = *current++;
				*targetrow++ = *current++;
				*targetrow++ = *current++;
				bgrow += 3;
			} else {
				b1 = *bgrow++;
				g1 = *bgrow++;
				r1 = *bgrow++;

				b2 = *current++;
				g2 = *current++;
				r2 = *current++;

				// 权重
				wt = m / 255.0;
				
				// 混合
				b = b1*wt + b2*(1.0 - wt);
				g = g1*wt + g2*(1.0 - wt);
				r = r1*wt + r2*(1.0 - wt);

				*targetrow++ = b;
				*targetrow++ = g;
				*targetrow++ = r;
			}
		}
	}

	return result;
}

 视频中绿布替换成风景背景：