填充ndarray以确保剪切时为负值

Question

因此，我目前正尝试使用两个因素（Bx和By）在python中剪切图像。问题是当我输入负值时，我会从数组中获得IndexError /超出范围。

我相信我必须做一些填充，但是我不知道将其应用于代码吗？

import cv2
import numpy

#Load the source image
src = cv2.imread("lena.png")

rows, cols, c = src.shape

# x1 = x + y · Bx
# y1 = y + x · By
Bx = 0.0
By = 0.5

imgForward = numpy.ndarray(shape = (int (cols + rows*By), int (rows + cols*Bx), 3))

for row in range(rows):
    for col in range(cols):
        imgForward[int (row+col*By), int(col+row*Bx)] = src[row,col]/255

cv2.imshow("Forward mapping", imgForward)

cv2.waitKey(0)