How exactly does the dp parameter in the houghcircle function in the opencv library work?
I am trying to understand the function and I am not quite sure how it affects the results. .houghcircles()
dp
Picking up http://docs.opencv.org/modules/imgproc/doc/feature_detection.html?highlight=houghcircles#houghcircles it says:
dp
- the inverse ratio of the resolution of the battery to the image For example, if thedp=1
battery has the same resolution as the input image.
Ifdp=2
, the sum of the accumulator is half the width and height.
Let's say you have a 1000x1000 image. Then you set dp to 3 so the battery only sees 1/3 of the image? Or is it something like, the image size remains the same but the number of pixels is smaller? those. when 3 pixels of the original image correlate with 1 pixel that the drive sees, for example, the original image is "blurry"?
I was able to pinpoint the exact number of red apples in a bowl by understanding other parameters and then tinker with dp
.
Perhaps my understanding of accumulator is wrong since they are correlated? From what I understand this is the number of times the region has "hit", but I'm not sure how it calculates the "hit area"
My code takes a bowl of apples, converts to HSV, captures reddish hues, converts it to black or white (not grayscale) using bitWiseOr, then does some .erode()
/ .dilate()
to reduce noise, then .houghcircles()
.
The resulting image looks like this http://i.imgur.com/iGyr7TG.jpg
Thanks in advance.
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Verba Associate Professor,
Exempla trahunt.
Best Image in Interactive GUI
Configurable UI panel allows you to customize the parameter (s) by moving multiple sliders
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()
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