opencv學習筆記30-點多邊形測試-pointPolygonTest（計算每個點到輪廓的距離）

只用來記錄學習筆記

畫一個6變形：

	const int r = 100;
	Mat src = Mat::zeros(r * 4, r * 4, CV_8UC1);
	 
	vector<Point2f> vert(6);
	vert[0] = Point(3 * r / 2, static_cast<int>(1.34*r));
	vert[1] = Point(1 * r, 2 * r);
	vert[2] = Point(3 * r / 2, static_cast<int>(2.66*r));
	vert[3] = Point(5 * r / 2, static_cast<int>(2.66*r));
	vert[4] = Point(3 * r, 2 * r);
	vert[5] = Point(5 * r / 2, static_cast<int>(1.34*r));

	for (int i = 0; i < 6; i++) {
		line(src, vert[i], vert[(i + 1) % 6], Scalar(255), 3, 8, 0);
	}

獲取每個點到輪廓的距離：

	vector<vector<Point>> contours; //輪廓
	vector<Vec4i> hierachy;
	findContours(src, contours, hierachy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));//獲取輪廓
	Mat raw_dist = Mat::zeros(src.size(), CV_32FC1);
	for (int row = 0; row < raw_dist.rows; row++) {
		for (int col = 0; col < raw_dist.cols; col++) {
			double dist = pointPolygonTest(contours[0], Point2f(static_cast<float>(col), static_cast<float>(row)), true);
			//contours[0]: 輸入的輪廓
			//Point2f(static_cast<float>(col), static_cast<float>(row)): 測試點
			//true:是否返回距離值，如果是false，1表示在內面，0表示在邊界上，-1表示在外部，true返回實際距離
			raw_dist.at<float>(row, col) = static_cast<float>(dist); //把每一個像素點都用距離值代替
		}
	}

根據距離的大小用不同的顏色填充，就變成了漸變色：

double minValue, maxValue;
	minMaxLoc(raw_dist, &minValue, &maxValue, 0, 0, Mat());//在一個數組中找到全局最小值和全局最大值,該函數不能用於多通道數組
	Mat drawImg = Mat::zeros(src.size(), CV_8UC3);
	for (int row = 0; row < drawImg.rows; row++) {
		for (int col = 0; col < drawImg.cols; col++) {
			float dist = raw_dist.at<float>(row, col); //讀取每一個點到輪廓的距離
			if (dist > 0) { //點在輪廓內
				drawImg.at<Vec3b>(row, col)[0] = (uchar)abs((dist / maxValue) * 255);//abs絕對值函數， 
				//藍色：離輪廓越遠，藍色越深
			}
			else if (dist < 0) { //點在輪廓外
				drawImg.at<Vec3b>(row, col)[2] = (uchar)abs((dist / minValue) * 255);
				//紅色：離輪廓越遠，紅色越深
			}
			else {//點在輪廓上dist=0
				drawImg.at<Vec3b>(row, col)[0] = (uchar)abs(255 - dist);
				drawImg.at<Vec3b>(row, col)[1] = (uchar)abs(255 - dist);
				drawImg.at<Vec3b>(row, col)[2] = (uchar)abs(255 - dist);
				// 255,255,255 白色
			}
		}
	}

效果圖：