无法在opencv python中将图像转换为灰色

Question

在执行一些需要灰度图像的其他操作之前，下面的代码是初步的。 问题是我转换为灰度似乎没有用，执行imshow（test）时，显示为紫色和蓝色。

%matplotlib inline
import matplotlib.image as mpimg
from matplotlib import pyplot as plt

red_image = mpimg.imread('/vagrant/notebooks/red_thing.jpg')

import cv2
import numpy as np
hsv = cv2.cvtColor(red_image, cv2.COLOR_BGR2HSV)
lower_red = np.array([30,150,50])
upper_red = np.array([255,255,180])

mask = cv2.inRange(hsv, lower_red, upper_red)
res = cv2.bitwise_and(red_image,red_image, mask= mask)

# this should be grayscale but when I display it, it contains color:
test = cv2.cvtColor(res, cv2.COLOR_BGR2GRAY)

Answer 1

我解决了

cv2.cvtColor（res，cv2.COLOR_HSV2RGB）