OpenCV与AI深度学习 | 实战 | OpenCV中更稳更快的找圆方法--EdgeDrawing使用演示（详细步骤 + 代码）

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原文链接：实战 | OpenCV中更稳更快的找圆方法--EdgeDrawing使用演示（详细步骤 + 代码）

导读

本文主要介绍如何在OpenCV中使用EdgeDrawing模块查找圆(详细步骤 + 代码)。

背景介绍

从OpenCV4.5.2开始，Contrib模块中封装了开源库ED_Lib用于查找图像中的直线、线段、椭圆和圆。Github地址：

https://github.com/CihanTopal/ED_Lib

算法原理简介：

边缘绘制（ED）算法是一种解决边缘检测问题的主动方法。与许多其他遵循减法方法的现有边缘检测算法相比（即在图像上应用梯度滤波器后，根据多种规则消除像素，例如 Canny 中的非极大值抑制和滞后），ED 算法通过加法策略工作，即逐一选取边缘像素，因此称为“边缘绘制”。然后我们处理这些随机形状的边缘段以提取更高级别的边缘特征，即直线、圆、椭圆等。从阈值梯度幅度中提取边缘像素的流行方法是非极大值抑制，它测试每个像素是否具有最大值沿其梯度方向的梯度响应，如果没有则消除。然而，此方法不检查相邻像素的状态，因此可能会导致低质量（在边缘连续性、平滑度、薄度、定位方面）边缘片段。ED 不是非极大值抑制，而是指向一组边缘像素，并通过最大化边缘段的总梯度响应来将它们连接起来。因此，它可以提取高质量的边缘片段，而不需要额外的滞后步骤。

OpenCV中使用介绍文档：

https://docs.opencv.org/4.5.2/d1/d1c/classcv_1_1ximgproc_1_1EdgeDrawing.html

使用步骤

EdgeDrawing类是在Contrib的ximgproc模块中，C++中使用它需要满足以下条件：

① OpenCV >= 4.5.2

② CMake编译Contrib模块

③ 包含edge_drawing.hpp头文件

Python中使用需要安装opencv-python-contrib >=4.5.2

【1】Python中使用演示：

#公众号--OpenCV与AI深度学习
'''
This example illustrates how to use cv.ximgproc.EdgeDrawing class.
Usage:ed.py [<image_name>]    image argument defaults to board.jpg
'''
# Python 2/3 compatibility
from __future__ import print_function
import numpy as np
import cv2 as cv
import random as rng
import sysrng.seed(12345)def main():try:fn = sys.argv[1]except IndexError:fn = 'board.jpg'src = cv.imread(cv.samples.findFile(fn))gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)cv.imshow("source", src)ssrc = src.copy() * 0lsrc = src.copy()esrc = src.copy()ed = cv.ximgproc.createEdgeDrawing()# you can change parameters (refer the documentation to see all parameters)EDParams = cv.ximgproc_EdgeDrawing_Params()EDParams.MinPathLength = 50     # try changing this value between 5 to 1000EDParams.PFmode = False         # default value try to switch it to TrueEDParams.MinLineLength = 20     # try changing this value between 5 to 100EDParams.NFAValidation = True   # default value try to switch it to Falseed.setParams(EDParams)# Detect edges# you should call this before detectLines() and detectEllipses()ed.detectEdges(gray)segments = ed.getSegments()lines = ed.detectLines()ellipses = ed.detectEllipses()# Draw detected edge segmentsfor i in range(len(segments)):color = (rng.randint(0,256), rng.randint(0,256), rng.randint(0,256))cv.polylines(ssrc, [segments[i]], False, color, 1, cv.LINE_8)cv.imshow("detected edge segments", ssrc)# Draw detected linesif lines is not None:  # Check if the lines have been found and only then iterate over these and add them to the imagelines = np.uint16(np.around(lines))for i in range(len(lines)):cv.line(lsrc, (lines[i][0][0], lines[i][0][1]), (lines[i][0][2], lines[i][0][3]), (0, 0, 255), 1, cv.LINE_AA)cv.imshow("detected lines", lsrc)# Draw detected circles and ellipsesif ellipses is not None:  # Check if circles and ellipses have been found and only then iterate over these and add them to the imagefor i in range(len(ellipses)):center = (int(ellipses[i][0][0]), int(ellipses[i][0][1]))axes = (int(ellipses[i][0][2])+int(ellipses[i][0][3]), int(ellipses[i][0][2])+int(ellipses[i][0][4]))angle = ellipses[i][0][5]color = (0, 0, 255)if ellipses[i][0][2] == 0:color = (0, 255, 0)cv.ellipse(esrc, center, axes, angle, 0, 360, color, 2, cv.LINE_AA)cv.imshow("detected circles and ellipses", esrc)cv.waitKey(0)print('Done')if __name__ == '__main__':print(__doc__)main()
cv.destroyAllWindows()

执行指令：ed.py [<image_name>]

实例1: edge_drawing.py 1.png

实例2: edge_drawing.py 2.png

实例3: edge_drawing.py 3.png

说明：上述图中，绿色表示找到的椭圆，红色表示找到的圆。

当然，EdgeDrawing还可以获取边缘信息和查找直线，效果如下：

【2】C++中使用演示：

//公众号--OpenCV与AI深度学习
#include <iostream>
#include <opencv2/opencv.hpp>
#include <opencv2/ximgproc/edge_drawing.hpp>using namespace std;
using namespace cv;
using namespace ximgproc;int main() {Mat src = imread("./imgs/11.bmp");if (src.empty()) {cout << "src image is empty, check again!" << endl;return -1;}// resize(src, src, Size(), 0.2, 0.2);imshow("src", src);Mat gray;cvtColor(src, gray, COLOR_BGR2GRAY);double start = static_cast<double>(getTickCount()); //计时开始Ptr<EdgeDrawing> ed = createEdgeDrawing();ed->params.EdgeDetectionOperator = EdgeDrawing::PREWITT;ed->params.MinPathLength = 50; // try changing this value between 5 to 1000ed->params.PFmode = false; // default value try to switch it to trueed->params.MinLineLength = 10; // try changing this value between 5 to 100ed->params.NFAValidation = false; // default value try to switch it to falseed->params.GradientThresholdValue = 20;ed->detectEdges(gray);vector<Vec4i> lines = ed->detectLines();vector<Vec7f> ellipses = ed->detectEllipses();Mat src_edges, src_lines, src_ellipses;src_edges = src.clone();src_lines = src.clone();src_ellipses = src.clone();for (size_t i = 0; i < lines.size(); i++) {line(src_lines, Point(lines[i][0], lines[i][1]), Point(lines[i][2], lines[i][3]), Scalar(0, 255, 0), 2, LINE_AA);}for (size_t i = 0; i < ellipses.size(); i++) {Vec3f c = ellipses[i].clone();ellipse(src_ellipses, Point(c[0], c[1]), Size(c[2], c[3]), c[4], 0, 360, Scalar(0, 0, 255), 2, LINE_AA);}imshow("Detected Edges", src_edges);imshow("Detected Lines", src_lines);imshow("Detected Ellipses", src_ellipses);waitKey(0);return 0;
}

实例1:

实例2:

实例3：

简单总结

总体来说EdgeDrawing提供的找圆和直线的方法简单易用且效果好，简单情况下使用默认参数即可。参数调整可以参考文档自己尝试，这里挑几个常用简单说明一下。

Ptr<EdgeDrawing> ed = createEdgeDrawing();
ed->params.EdgeDetectionOperator = EdgeDrawing::LSD;
ed->params.MinPathLength = 50; // try changing this value between 5 to 1000
ed->params.PFmode = false; //defaut value try to swich it to true
ed->params.MinLineLength = 10; // try changing this value between 5 to 100
ed->params.NFAValidation = true; // defaut value try to swich it to false
ed->params.GradientThresholdValue = 20;

【1】算法使用的梯度算子，可选4种，默认是PREWITT，大家可以设置不同的梯度算子尝试效果。