我正在尝试使用 opencv python 库使用 cv2.imwrite() function 将图像保存到文件，但它显示错误

Question

I am trying to save an image to a file by using the OpenCV python library using cv2.imwrite() but it shows an error.

The code is:

import cv2

# Reading image as gray scale
img = cv2.imread(r'C:\Users\Person\Pictures\Wallpapers (Space)\Carl Sagan.jpg',1)
# saving the image
status = cv2.imwrite(r'C:\Users\Person\Pictures\Wallpapers (Space)\Carl Sagan.jpg',0,img)

print('the status of the image is : ',status)

Error displayed:

error                                     Traceback (most recent call last)
<ipython-input-4-773a1fcb9cd4> in <module>
      4 img = cv2.imread(r'C:\Users\Joydeep\Pictures\Wallpapers (Space)\Carl Sagan.jpg',1)
      5 # saving the image
----> 6 status = cv2.imwrite(r'C:\Users\Joydeep\Pictures\Wallpapers (Space)\Carl Sagan.jpg',0,img)
      7 
      8 print('the status of the image is : ',status)

error: OpenCV(4.5.2) :-1: error: (-5:Bad argument) in function 'imwrite'
> Overload resolution failed:
>  - Conversion error: params, what: OpenCV(4.5.2) C:\Users\runneradmin\AppData\Local\Temp\pip-req-build-inblc7p7\opencv\modules\core\src\copy.cpp:320: error: (-215:Assertion failed) channels() == CV_MAT_CN(dtype) in function 'cv::Mat::copyTo'
> 
>  - Conversion error: params, what: OpenCV(4.5.2) C:\Users\runneradmin\AppData\Local\Temp\pip-req-build-inblc7p7\opencv\modules\core\src\copy.cpp:320: error: (-215:Assertion failed) channels() == CV_MAT_CN(dtype) in function 'cv::Mat::copyTo'
> 

*** What should I do?

Answer 1

According to the docs , imwrite have the following parameters:

cv.imwrite( filename, img[, params] )

where params are the ImwriteFlags to specify the output.

so it is probably the 0 , try:

status = cv2.imwrite(r'C:\Users\Person\Pictures\Wallpapers (Space)\Carl Sagan.jpg',img)

Answer 2

First of all, when you use 1 as the second parameter of the cv2.imread() method, it will read in the image in full color rather than grayscale; note that 1 is the default value for the flag. In order to read in the image as a grayscale image, use 0 , which is the value for cv2.IMREAD_GRAYSCALE .

Finally, you don't include the 0 when you're writing the image:

import cv2

img = cv2.imread(r'C:\Users\Person\Pictures\Wallpapers (Space)\Carl Sagan.jpg', 0)
status = cv2.imwrite(r'C:\Users\Person\Pictures\Wallpapers (Space)\Carl Sagan.jpg', img)

print('the status of the image is : ', status)

If you prefer to read in the image in color, and only write it out in grayscale, you can use the cv2.cvtColor method:

import cv2

img = cv2.imread(r'C:\Users\Person\Pictures\Wallpapers (Space)\Carl Sagan.jpg')
status = cv2.imwrite(r'C:\Users\Person\Pictures\Wallpapers (Space)\Carl Sagan.jpg', cv2.cvtColor(img, 6))

print('the status of the image is : ', status)

Where the 6 is the value of cv2.COLOR_BGR2GRAY .