如何使用 OpenCV 检测简单的几何形状 [英] How to detect simple geometric shapes using OpenCV

问题描述

我有这个项目，我需要(在 iOS 上)检测图像中的简单几何形状.

在互联网上搜索后，我得出结论，最好的工具是 OpenCV.问题是，直到两个小时前，我都不知道 OpenCV 是什么，我什至从未远程做过任何涉及图像处理的事情.我的主要经验是 JS/HTML,C#,SQL,Objective-C...

我从哪里开始?

我找到了这个.

关于 iOS，OpenCV 开发人员今年夏天正在开发一些 iOS 示例，因此请访问他们的网站:www.code.opencv.org 并与他们联系.

你可以在这里找到他们教程的幻灯片:http:///code.opencv.org/svn/gsoc2012/ios/trunk/doc/CVPR2012_OpenCV4IOS_Tutorial.pdf

I have this project where I need (on iOS) to detect simple geometric shapes inside an image.

After searching the internet I have concluded that the best tool for this is OpenCV. The thing is that up until two hours ago I had no idea what OpenCV is and I have never even remotely did anything involving image processing. My main experience is JS/HTML,C#,SQL,Objective-C...

Where do I start with this?

I have found this answer that I was able to digest and by reading already other stuff, I understand that OpenCV should return an Array of shapes with the points/corners, is this true? Also how will it represent a circle or a half circle? Also what about the shape orientation?

Do you know of any Demo iOS project that can demonstrate a similar functionality?

解决方案

If you have only these regular shapes, there is a simple procedure as follows :

1. Find Contours in the image ( image should be binary as given in your question)
2. Approximate each contour using approxPolyDP function.
3. First, check number of elements in the approximated contours of all the shapes. It is to recognize the shape. For eg, square will have 4, pentagon will have 5. Circles will have more, i don't know, so we find it. ( I got 16 for circle and 9 for half-circle.)
4. Now assign the color, run the code for your test image, check its number, fill it with corresponding colors.

Below is my example in Python:

import numpy as np
import cv2

img = cv2.imread('shapes.png')
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

ret,thresh = cv2.threshold(gray,127,255,1)

contours,h = cv2.findContours(thresh,1,2)

for cnt in contours:
    approx = cv2.approxPolyDP(cnt,0.01*cv2.arcLength(cnt,True),True)
    print len(approx)
    if len(approx)==5:
        print "pentagon"
        cv2.drawContours(img,[cnt],0,255,-1)
    elif len(approx)==3:
        print "triangle"
        cv2.drawContours(img,[cnt],0,(0,255,0),-1)
    elif len(approx)==4:
        print "square"
        cv2.drawContours(img,[cnt],0,(0,0,255),-1)
    elif len(approx) == 9:
        print "half-circle"
        cv2.drawContours(img,[cnt],0,(255,255,0),-1)
    elif len(approx) > 15:
        print "circle"
        cv2.drawContours(img,[cnt],0,(0,255,255),-1)

cv2.imshow('img',img)
cv2.waitKey(0)
cv2.destroyAllWindows()

Below is the output:

Remember, it works only for regular shapes.

Alternatively to find circles, you can use houghcircles. You can find a tutorial here.

Regarding iOS, OpenCV devs are developing some iOS samples this summer, So visit their site : www.code.opencv.org and contact them.

You can find slides of their tutorial here : http://code.opencv.org/svn/gsoc2012/ios/trunk/doc/CVPR2012_OpenCV4IOS_Tutorial.pdf

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