功能：

建立一個滑動條來控制檢測直線的長度閾值，即大於該閾值的檢測出來，小於該閾值的忽略
注意：這裡用的函式是HoughLinesP而不是HoughLines，因為HoughLinesP直接給出了直線的斷點，在畫出線段的時候可以偷懶

程式碼：

# -*- coding: utf-8 -*- 

import cv2

#兩個回撥函式
def HoughLinesP(minLineLength):
    global minLINELENGTH 
    minLINELENGTH = minLineLength + 1
    print "minLINELENGTH:",minLineLength + 1
 

    tempIamge = scr.copy()
    lines = cv2.HoughLinesP( edges, 1, cv2.cv.CV_PI/180, minLINELENGTH, 0 )
    for x1,y1,x2,y2 in lines[0]:
        cv2.line(tempIamge,(x1,y1),(x2,y2),(0,255,0),1)
    cv2.imshow(window_name,tempIamge)

#臨時變數
minLineLength = 20

#全域性變數
minLINELENGTH = 20
max_value = 100
window_name = "HoughLines Demo"
 

trackbar_value = "minLineLength"

#讀入圖片，模式為灰度圖，建立視窗
scr = cv2.imread("G:\\homework\\building.bmp")
gray = cv2.cvtColor(scr,cv2.COLOR_BGR2GRAY)
img = cv2.GaussianBlur(gray,(3,3),0)
edges = cv2.Canny(img, 50, 150, apertureSize = 3)
cv2.namedWindow(window_name)

#建立滑動條
cv2.createTrackbar( trackbar_value, window_name, \
                    minLineLength, max_value, HoughLinesP)

#初始化
 

HoughLinesP(20)

if cv2.waitKey(0) == 27:  
    cv2.destroyAllWindows()

呼叫：

>>> import os
>>> os.chdir("g:\homework")
>>> 
>>> import HoughLines
minLINELENGTH: 20
minLINELENGTH: 21
minLINELENGTH: 22
minLINELENGTH: 23
minLINELENGTH: 25
minLINELENGTH: 26
minLINELENGTH: 27
minLINELENGTH: 28

效果圖：