cv2.imshow() 函数在用户输入时不显示图像，否则工作

Question

我正在编写代码以在 500x500 白色图像上生成用户定义的网格。 程序应要求用户输入网格大小并相应地绘制垂直和水平线并最终显示图像。

我面临的问题是，每当我调用“getGridSize()”函数时，图像都不会显示。但是当我手动为变量“num”赋值时，图像显示会起作用

我也尝试过使用 cv2.waitKey(0) 和 cv2.destroyAllWindows() 但没有成功。

import cv2
import numpy as np

width = 500 # Dimensions of the blank, white image

def main():
##    getGridSize()
    num = 4

    generateWhiteImg()
    lineImg = whiteImg.copy() # Create a copy of the white image to draw upon

    for i in range(0, num):
        spacing = int(width / (num + 1))    # Specify the width between each line, for uniform placement
        point = (i + 1) * spacing   # Change the coordinate of the lines to be drawn by fixed amounts
        lineImg = cv2.line(lineImg, (0, point), (width, point), (0, 0, 0), 3)   # Draw horizontal lines
        lineImg = cv2.line(lineImg, (point, 0), (point, width), (0, 0, 0), 3)   # Draw vertical lines

    cv2.imshow('LINES', lineImg)

## Function to get grid size from user
def getGridSize():
    global num # Stores the size of grid to be drawn
    num = input("Enter the size of blank grid: ")
    num = int(num) # To convert string to integer

## Function to generate a blank, white image
def generateWhiteImg():
    global whiteImg
    img = np.zeros((width, width, 3), np.uint8) # Generate a zeros list, i.e., a black image
    img[:width] = (255, 255, 255) # Convert black image to white
    cv2.imwrite('whiteImg.png', img) # Save the white image
    whiteImg = cv2.imread('whiteImg.png')   # Load the same from directory

if __name__ == "__main__":
    main()

没有错误消息。 我希望代码能按原样工作。我认为问题出在 getGridSize() 函数内部

更新 1：我为此使用 python 3.5.4

Answer 1

当您使用 OpenCV 进行 GUI 操作时，您总是需要在之后调用 cv2.waitKey() 方法。它确保显示窗口和determines how long the window will stay open。