OpenCV: get Hough accumulator value?

Question

Is it possible to get the accumulator value along with rho and theta from a Hough transform?

I ask because I\'d like to differentiate betwe

Answer 1

Although this is an old question, I had the same problem, so I might as well put up my solution. The threshold in houghlines() returns 1 for any point that cleared the threshold for votes. The solution is to run houghlines() for every threshold value (until there are no more votes) and add up the votes in another array. In python (maybe with other languages too) when you have no more votes, it throws an error, so use try/except.

Here is an example in python. The array I used was for rho values of -199 to 200 with a max vote of less than 100. You can play around with those constants to suit your needs. You may need to add a line to convert the source image to grayscale.

import matplotlib.pyplot as plt

import cv2

import math



############ make houghspace array ############

houghspace = []

c = 0

height = 400

while c <= height:

    houghspace.append([])

    cc = 0

    while cc <= 180:

        houghspace[c].append(0)

        cc += 1

    c+=1



############ do transform ############


degree_tick = 1 #by how many degrees to check 

total_votes = 1 #votes counter

highest_vote = 0 #highest vote in the array



while total_votes < 100:

    img = cv2.imread('source.pgm')

    edges = cv2.Canny(img,50,150,apertureSize = 3)

    lines = cv2.HoughLines(edges,1,math.pi*degree_tick/180,total_votes)



    try:

        for rho,theta in lines[0]:





            a = math.cos(theta)

            b = math.sin(theta)

            x1 = int((a*rho) + 1000*(-b))

            y1 = int((b*rho) + 1000*(a))

            x2 = int((a*rho) - 1000*(-b))

            y2 = int((b*rho) - 1000*(a))

            cv2.line(img,(x1,y1),(x2,y2),(50,200,255),2)

        #################add votes into the array################

        deradian = 180/math.pi #used to convert to degrees

        for rho,theta in lines[0]:

            degree = int(round(theta*deradian))

            rho_pos = int(rho - 200) 

            houghspace[rho_pos][degree] += 1 
    #when lines[0] has no votes, it throws an error which is caught here

    except:     

        total_votes = 999 #exit loop


    highest_vote = total_votes

    total_votes += 1
    del lines



########### loop finished ###############################
print highest_vote



#############################################################

################### plot the houghspace ###################


maxy = 200 #used to offset the y-axis

miny = -200 #used to offset the y-axis

#the main graph

fig = plt.figure(figsize=(10, 5))

ax = fig.add_subplot(111)

ax.set_title('Houghspace')

plt.imshow(houghspace, cmap='gist_stern')

ax.set_aspect('equal')

plt.yticks([0,-miny,maxy-miny], [miny,0,maxy])

#the legend
cax = fig.add_axes([0, 0.1, 0.78, 0.8])

cax.get_xaxis().set_visible(False)

cax.get_yaxis().set_visible(False)

cax.patch.set_alpha(0)

cax.set_frame_on(False)

plt.colorbar(orientation='vertical')

#plot

plt.show()