OpenCV库中houghcircle函数中的dp参数具体是如何工作的？

Question

我正在尝试理解.houghcircles()函数，但我并没有完全理解dp如何影响结果。

在http://docs.opencv.org/modules/imgproc/doc/feature_detection.html?highlight=houghcircles#houghcircles中查找，它说： dp - 累加器分辨率与图像分辨率的反比例关系。例如，如果dp=1，则累加器具有与输入图像相同的分辨率。如果dp=2，则累加器的宽度和高度减半。

假设您有一个1000x1000的图像。然后将dp设置为3，因此累加器只看到图像的1/3？或者是像原始图像被“模糊”一样，图像大小保持不变，但所看到的像素数量更少吗？即原始图像中的每3个像素对应于累加器看到的1个像素？

通过了解其他参数并调整dp，我已成功检测出碗中红苹果的数量。

也许我的累加器理解不正确，因为两者是相关的？据我所知，它是区域被“命中”的次数，但我不确定它如何计算“命中区域”。

我的代码将苹果碗转换为HSV，获取红色色调，使用bitWiseOr将其转换为黑色或白色（不是灰度格式），然后进行一些.erode()/.dilate()以减少噪声，然后进行.houghcircles()。

我的结果图像如下：http://i.imgur.com/iGyr7TG.jpg 提前致谢。

- PGT

Answer 1

言传身教，
以身作则。

最好在交互式GUI演示中查看

可配置的UI面板允许通过移动几个滑块来调整参数

---

import sys
import cv2
import math
import numpy
from scipy.ndimage import label
pi_4 = 4*math.pi

def nothing_asCallback(x):
    pass

def GUI_openCV_circles():
    # --------------------------------------------------------------------------------GUI-<image>
    frame = cv2.imread(  "openCV_CircleDetection_IMG_LASSO_AREA.JPG" )
    demo  = frame[:800,:800,:]
    # --------------------------------------------------------------------------------GUI-<window>-s
    cv2.namedWindow( "DEMO.IN",             cv2.cv.CV_WINDOW_AUTOSIZE )
    cv2.namedWindow( "DEMO.Canny",          cv2.cv.CV_WINDOW_AUTOSIZE )
    cv2.namedWindow( "DEMO.Canny.Circles",  cv2.cv.CV_WINDOW_AUTOSIZE )
    # --------------------------------------------------------------------------------GUI-<state>-initial-value(s)
    aKeyPRESSED                                     = None              # .init

    aCanny_LoTreshold                               = 127
    aCanny_LoTreshold_PREVIOUS                      =  -1
    aCanny_HiTreshold                               = 255
    aCanny_HiTreshold_PREVIOUS                      =  -1

    aHough_dp                                       =   1
    aHough_dp_PREVIOUS                              =  -1
    aHough_minDistance                              =  10
    aHough_minDistance_PREVIOUS                     =  -1
    aHough_param1_aCannyHiTreshold                  = 255
    aHough_param1_aCannyHiTreshold_PREVIOUS         =  -1
    aHough_param2_aCentreDetectTreshold             =  20
    aHough_param2_aCentreDetectTreshold_PREVIOUS    =  -1
    aHough_minRadius                                =  10
    aHough_minRadius_PREVIOUS                       =  -1
    aHough_maxRadius                                =  30
    aHough_maxRadius_PREVIOUS                       =  -1
    # --------------------------------------------------------------------------------GUI-<ACTOR>-s
    cv2.createTrackbar( "Lo_Treshold",          "DEMO.Canny",          aCanny_LoTreshold,                      255, nothing_asCallback )
    cv2.createTrackbar( "Hi_Treshold",          "DEMO.Canny",          aCanny_HiTreshold,                      255, nothing_asCallback )

    cv2.createTrackbar( "dp",                   "DEMO.Canny.Circles",  aHough_dp,                              255, nothing_asCallback )
    cv2.createTrackbar( "minDistance",          "DEMO.Canny.Circles",  aHough_minDistance,                     255, nothing_asCallback )
    cv2.createTrackbar( "param1_HiTreshold",    "DEMO.Canny.Circles",  aHough_param1_aCannyHiTreshold,         255, nothing_asCallback )
    cv2.createTrackbar( "param2_CentreDetect",  "DEMO.Canny.Circles",  aHough_param2_aCentreDetectTreshold,    255, nothing_asCallback )
    cv2.createTrackbar( "minRadius",            "DEMO.Canny.Circles",  aHough_minRadius,                       255, nothing_asCallback )
    cv2.createTrackbar( "maxRadius",            "DEMO.Canny.Circles",  aHough_maxRadius,                       255, nothing_asCallback )

    cv2.imshow( "DEMO.IN",          demo )                              # static ...
    # --------------------------------------------------------------------------------GUI-mainloop()
    print " --------------------------------------------------------------------------- press [ESC] to exit "
    while( True ):
        # --------------------------------------------------------------------------------GUI-[ESCAPE]?
        if aKeyPRESSED == 27:
            break
        # --------------------------------------------------------------------------------<vars>-DETECT-delta(s)
        aCanny_LoTreshold = cv2.getTrackbarPos( "Lo_Treshold", "DEMO.Canny" )
        aCanny_HiTreshold = cv2.getTrackbarPos( "Hi_Treshold", "DEMO.Canny" )

        if (    aCanny_LoTreshold      != aCanny_LoTreshold_PREVIOUS
            or  aCanny_HiTreshold      != aCanny_HiTreshold_PREVIOUS
            ):
            # --------------------------= FLAG
            aCannyRefreshFLAG           = True
            # --------------------------= RE-SYNC
            aCanny_LoTreshold_PREVIOUS  = aCanny_LoTreshold
            aCanny_HiTreshold_PREVIOUS  = aCanny_HiTreshold
        else:
            # --------------------------= Un-FLAG
            aCannyRefreshFLAG           = False

        aHough_dp                           = cv2.getTrackbarPos( "dp",                 "DEMO.Canny.Circles" )
        aHough_minDistance                  = cv2.getTrackbarPos( "minDistance",        "DEMO.Canny.Circles" )
        aHough_param1_aCannyHiTreshold      = cv2.getTrackbarPos( "param1_HiTreshold",  "DEMO.Canny.Circles" )
        aHough_param2_aCentreDetectTreshold = cv2.getTrackbarPos( "param2_CentreDetect","DEMO.Canny.Circles" )
        aHough_minRadius                    = cv2.getTrackbarPos( "minRadius",          "DEMO.Canny.Circles" )
        aHough_maxRadius                    = cv2.getTrackbarPos( "maxRadius",          "DEMO.Canny.Circles" )

        if (    aHough_dp                            != aHough_dp_PREVIOUS
            or  aHough_minDistance                   != aHough_minDistance_PREVIOUS
            or  aHough_param1_aCannyHiTreshold       != aHough_param1_aCannyHiTreshold_PREVIOUS
            or  aHough_param2_aCentreDetectTreshold  != aHough_param2_aCentreDetectTreshold_PREVIOUS    
            or  aHough_minRadius                     != aHough_minRadius_PREVIOUS
            or  aHough_maxRadius                     != aHough_maxRadius_PREVIOUS
            ):
            # --------------------------= FLAG
            aHoughRefreshFLAG           = True                  
            # ----------------------------------------------= RE-SYNC
            aHough_dp_PREVIOUS                              =  aHough_dp                          
            aHough_minDistance_PREVIOUS                     =  aHough_minDistance                 
            aHough_param1_aCannyHiTreshold_PREVIOUS         =  aHough_param1_aCannyHiTreshold     
            aHough_param2_aCentreDetectTreshold_PREVIOUS    =  aHough_param2_aCentreDetectTreshold
            aHough_minRadius_PREVIOUS                       =  aHough_minRadius                   
            aHough_maxRadius_PREVIOUS                       =  aHough_maxRadius                   
        else:
            # --------------------------= Un-FLAG
            aHoughRefreshFLAG           = False
        # --------------------------------------------------------------------------------REFRESH-process-pipe-line ( with recent <state> <vars> )
        if ( aCannyRefreshFLAG ):

            edges   = cv2.Canny(        demo,   aCanny_LoTreshold,
                                                aCanny_HiTreshold
                                        )
            # --------------------------------------------------------------------------------GUI-SHOW-Canny()-<edges>-onRefreshFLAG
            cv2.imshow( "DEMO.Canny",   edges )
            pass

        if ( aCannyRefreshFLAG or aHoughRefreshFLAG ):

            circles = cv2.HoughCircles( edges,  cv2.cv.CV_HOUGH_GRADIENT,
                                                aHough_dp,
                                                aHough_minDistance,
                                                param1      = aHough_param1_aCannyHiTreshold,
                                                param2      = aHough_param2_aCentreDetectTreshold,
                                                minRadius   = aHough_minRadius,
                                                maxRadius   = aHough_maxRadius
                                        )
            # --------------------------------------------------------------------------------GUI-SHOW-HoughCircles()-<edges>-onRefreshFLAG
            demoWithCircles = cv2.cvtColor( demo,            cv2.COLOR_BGR2RGB )                          # .re-init <<< src
            demoWithCircles = cv2.cvtColor( demoWithCircles, cv2.COLOR_RGB2BGR )

            for aCircle in circles[0]:
                cv2.circle( demoWithCircles,    ( int( aCircle[0] ), int( aCircle[1] ) ),
                                                aCircle[2],
                                                (0,255,0),
                                                1
                            )
                pass
            pass
            cv2.imshow( "DEMO.Canny.Circles", demoWithCircles )
        pass        
        # --------------------------------------------------------------------------------<vars>-UPDATE-<state>
        # ref. above in .onRefreshFLAG RE-SYNC sections
        # --------------------------------------------------------------------------------GUI-INPUT ? [ESCAPE]
        aKeyPRESSED = cv2.waitKey(1) & 0xFF
    pass
    # --------------------------------------------------------------------------------GUI-<window>-s / DESTROY
    cv2.destroyWindow( "DEMO.IN" )
    cv2.destroyWindow( "DEMO.Canny" )
    cv2.destroyWindow( "DEMO.Canny.Circles" )
    # --------------------------------------------------------------------------------GUI-<window>-s
    pass

def main():
    GUI_openCV_circles()
    return 0

if __name__ == '__main__':
    main()

- user3666197

---

我会接受这个答案，仅仅因为那个引用语——而且也因为这是唯一的答案，并且当我复制粘贴这段代码时可能会向我展示 dp 是什么。 - PGT

@PGT :o) 很好 -- 看一次，读一百遍以上。OpenCV RefMan说：dp – 累加器分辨率与图像分辨率的倒数。例如，如果 dp=1 ，累加器的分辨率与输入图像相同。如果 dp=2 ，累加器的宽度和高度减半。 - user3666197

@user3666197 你知道任何详细解释累加器的资料来源吗？ - ibininja