opencv（Python/c++）:轮廓检测（边界框、矩形区域，圆区域，凸轮廓，多边形算法approxPloyDP）

骑猪看日落 2022-03-16 11:38 854阅读 0赞

# Python版 #

*  找到正方形轮廓

import cv2
    import numpy as np
    
    img=np.zeros((200,200),dtype=np.uint8)
    img[50:150,50:150]=255
    
    ret,thresh=cv2.threshold(img,127,255,0)#threshold阈值
    image,contours,hierarchy=cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
    
    color=cv2.cvtColor(img,cv2.COLOR_GRAY2BGR)
    img=cv2.drawContours(color,contours,-1,(0,255,0),2)
    cv2.imshow('contours',color)
    cv2.waitKey()
    cv2.destroyAllWindows()

效果图：  
![在这里插入图片描述][20190227181917597.png]

*  找到不规则形状轮廓  
    **不过**我发现如果背景是纯白色的，会识别失败，所以要求背景是黑色的！！（**所以在实际识别的时候可能需要转变一些东西**）

--------------------

原图  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjc1NTM4NA_size_16_color_FFFFFF_t_70]![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjc1NTM4NA_size_16_color_FFFFFF_t_70 1]

import cv2
    import numpy as np
    
    img=cv2.pyrDown(cv2.imread('hammer.jpeg',cv2.IMREAD_UNCHANGED))#图像金字塔
    
    ret,thresh=cv2.threshold(cv2.cvtColor(img.copy(),cv2.COLOR_BGR2GRAY),127,255,cv2.THRESH_BINARY)
    
    image,contours,hier=cv2.findContours(thresh,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)
    
    
    for c in contours:
        #找到包围盒的坐标系
        x,y,w,h=cv2.boundingRect(c)
        cv2.rectangle(img,(x,y),(x+w,y+h),(0,255,0),3)#绿色
    
        #找到最小区域
        rect=cv2.minAreaRect(c)
    
        #计算最小区域矩形的坐标
        box=cv2.boxPoints(rect)
    
        #归一坐标值到整型int
        box=np.int0(box)
        #画轮廓
        cv2.drawContours(img,[box],0,(0,0,255),3)#此处红色0表示绘制轮廓数组里指定的轮廓
    
        #计算封闭圆的半径和中心点
        (x,y),radius=cv2.minEnclosingCircle(c)
    
        #变成整形int
        center=(int(x),int(y))
        radius=int(radius)
    
        #画圆
        img=cv2.circle(img,center,radius,(0,255,255),3)#黄色
    
        cv2.drawContours(img,contours,-1,(255,0,0),3)#蓝色-1表示绘制所有轮廓
        cv2.imwrite('contourshammer.jpeg',img)
        cv2.imshow('contours',img)
    cv2.waitKey()
    cv2.destroyAllWindows()

效果图  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjc1NTM4NA_size_16_color_FFFFFF_t_70 2]![在这里插入图片描述][20190227204847551.png]

*  凸函数  
    (在之前的代码上添加）

cnt=contours[0]
        epsilon=0.01*cv2.arcLength(cnt,True)
        approx=cv2.approxPolyDP(cnt,epsilon,True)#计算近似的多边形框
        hull=cv2.convexHull(cnt)#计算凸形状

# c++版 #

[20190227181917597.png]: /images/20220316/1ca19745da2c4885a11839464dddb4c8.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjc1NTM4NA_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20190227203833880.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjc1NTM4NA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjc1NTM4NA_size_16_color_FFFFFF_t_70 1]: /images/20220316/d99818a3acef46f894bd2bb4988516d4.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjc1NTM4NA_size_16_color_FFFFFF_t_70 2]: https://img-blog.csdnimg.cn/20190227203616796.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjc1NTM4NA==,size_16,color_FFFFFF,t_70
[20190227204847551.png]: /images/20220316/2218756bc2d14481a404e4682dc1a2eb.png