遞歸函數不能按預期工作

Question

我用cv2.imread讀取了附加的圖像，並想找到圖像對象的輪廓。 如果閾值過大，即如果cv2.findContours找到了好幾條輪廓，就應該cv2.findContours降低閾值，這樣到最后只能找到一個輪廓。 這就是為什么我寫了遞歸函數thresholdloop ，但不幸的是它沒有做它應該做的。

import cv2   

b = cv2.imread("test.tiff")

thresh_factor = 140


imgray_b = cv2.cvtColor(b,cv2.COLOR_BGR2GRAY)
ret_b,thresh_b = cv2.threshold(imgray_b,thresh_factor,255,0)

_, cb, _ = cv2.findContours(thresh_b, cv2.RETR_CCOMP, cv2.CHAIN_APPROX_NONE)


def thresholdloop(cb, thresh_factor, X):

    while X == False:
        if len(cb) > 1:
            thresh_factor = thresh_factor - 5
            ret_b, thresh_b = cv2.threshold(imgray_b, thresh_factor, 255, 0)
            _, cb, _ = cv2.findContours(thresh_b, cv2.RETR_CCOMP, cv2.CHAIN_APPROX_NONE)
            X = False
            return thresholdloop(cb, thresh_factor, X)
        else:
            X = True

X = False
thresholdloop(cb, thresh_factor, X)

Answer 1

問題似乎是您的函數試圖在不使用global關鍵字的情況下修改全局變量。 您可以通過從函數中刪除所有參數來修復它，而是執行

def thresholdloop():
    global ret_b
    global cb
    global thresh_b
    global thresh_factor
    # rest of function

但相反，我建議在全局范圍內使用一個簡單的while循環（即沒有函數）

# after first calculation of cb
while len(cb) > 1:
    thresh_factor = thresh_factor - 5
    ret_b, thresh_b = cv2.threshold(imgray_b, thresh_factor, 255, 0)
    _, cb, _ = cv2.findContours(thresh_b, cv2.RETR_CCOMP, cv2.CHAIN_APPROX_NONE)

或者像這樣，所以你不必在循環內和之前復制計算cb的代碼

b = cv2.imread("test.tiff")
thresh_factor = 145  # + 5
imgray_b = cv2.cvtColor(b,cv2.COLOR_BGR2GRAY)
while True:
    thresh_factor = thresh_factor - 5
    ret_b, thresh_b = cv2.threshold(imgray_b, thresh_factor, 255, 0)
    _, cb, _ = cv2.findContours(thresh_b, cv2.RETR_CCOMP, cv2.CHAIN_APPROX_NONE)
    if len(cb) == 1:
        break