cpp：91：错误：（ - 5）输入图像的类型应为CV_8UC3！在函数fastNlMeansDenoisingColored

Question

我有ubuntu 16.04.我已经安装了opencv2.4.9并尝试运行此代码

import numpy as np

import cv2

from matplotlib import pyplot as plt

img = cv2.imread('/home/Picture/a.jpg')

dst = cv2.fastNlMeansDenoisingColored(img,None,10,10,7,21) 

plt.subplot(121),plt.imshow(img)
p
lt.subplot(122),plt.imshow(dst)

plt.show()

但是我收到了这个错误 -

OpenCV Error: Bad argument (Type of input image should be CV_8UC3!) in fastNlMeansDenoisingColored, file /build/opencv-SviWsf/opencv-2.4.9.1+dfsg/modules/photo/src/denoising.cpp, line 91
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
cv2.error: /build/opencv-SviWsf/opencv-2.4.9.1+dfsg/modules/photo/src/denoising.cpp:91: error: (-5) Type of input image should be CV_8UC3! in function fastNlMeansDenoisingColored

如何解决此问题？