open cv error -215 scn 3 scn 4 in function cvtColor

Question

I m currently in Ubuntu 14 04  using python 2 7 and cv2    When I run this code    import numpy as np import cv2  img   cv2 imread  2015-05-27-191152 jpg  0  gray   cv2 cvtColor img  cv2 COLOR BGR2GRAY    it returns    File  face detection py   line 11  in  lt module gt      gray   cv2 cvtColor img  cv2 COLOR BGR2GRAY  cv2 error   home arthurckl Desktop opencv-3 0 0-rc1 modules imgproc src color cpp 7564  error   -215  scn    3    scn    4 in function cvtColor   I already searched here and one answer said that I could be loading my photo the wrong way  because it should have 3 dimensions  rows  columns and depth   When I print the img shape it returns only two numbers  so I must be doing it wrong  But I don t know the right way to load my photo

User · Answer

Here is what i observed when I used my own image sets in .jpg format. In the sample script available in Opencv doc, note that it has the undistort and crop the image lines as below:

# undistort
dst = cv2.undistort(img, mtx, dist, None, newcameramtx)

# crop the image
x,y,w,h = roi
dst = dst[y:y+h, x:x+w]
cv2.imwrite('calibresult.jpg',dst)

So, when we run the code for the first time, it executes the line cv2.imwrite('calibresult.jpg',dst) saving a image calibresult.jpg in the current directory. So, when I ran the code for the next time, along with my sample image sets that I used for calibrating the camera in jpg format, the code also tried to consider this newly added image calibresult.jpg due to which the error popped out

error: C:\builds\master_PackSlaveAddon-win64-vc12-static\opencv\modules\imgproc\src\color.cpp:7456: error: (-215) scn == 3 || scn == 4 in function cv::ipp_cvtColor

What I did was: I simply deleted that newly generated image after each run or alternatively changed the type of the image to say png or tiff type. That solved the problem. Check if you are inputting and writing calibresult of the same type. If so, just change the type.

User · Answer

Only pass name of the image  no need of 0   img cv2 imread  sample jpg

User · Answer

img   cv2 imread  2015-05-27-191152 jpg  0    The above line of code reads your image in grayscale color model  because of the 0 appended at the end  And if you again try to convert an already gray image to gray image it will show that error   So either use above style or try undermentioned code   img   cv2 imread  2015-05-27-191152 jpg   gray img   cv2 cvtColor img  cv2 COLOR BGR2GRAY

User · Answer

First thing you should check is that whether the image exists in the root directory or not  This is mostly due to image with height   0  Which means that cv2 imread imageName  is not reading the image

User · Answer

On OS X I realised  that while cv2 imread can deal with  filename jpg  it can not process  file name jpg   Being a novice to python  I can t yet propose a solution  but as Fran  ois Leblanc wrote  it is more of a silent imread error   So it has a problem with an additional dot in the filename and propabely other signs as well  as with      Space  or     and so on

User · Answer

i think it because cv2 imread cannot read  jpg picture  you need to change  jpg to  png

User · Answer

This answer if for the people experiencing the same problem trying to accessing the camera    import numpy as np import cv2  cap   cv2 VideoCapture 0   while True         Capture frame-by-frame     ret  frame   cap read          Our operations on the frame come here     gray   cv2 cvtColor frame  cv2 COLOR BGR2GRAY        Display the resulting frame     cv2 imshow  frame  gray      if cv2 waitKey 1   amp  0xFF    ord  q            break    When everything done  release the capture cap release   cv2 destroyAllWindows     Using Linux   if you are trying to access the camera from your computer most likely there is a permission issue  try running the python script with sudo it should fix it   sudo python python script py   To test if the camera is accessible run the following command    ffmpeg -f v4l2 -framerate 25 -video size 640x480 -i  dev video0 output mkv

User · Answer

Give the full path of image with forward slash  It solved the error for me   E g   import numpy as np import cv2  img   cv2 imread  C  Python34 images 2015-05-27-191152 jpg   gray   cv2 cvtColor img  cv2 COLOR BGR2GRAY    Also  if you give 0 in second parameter while loading image using cv2 imread than no need to convert image using cvtColor  it is already loaded as grayscale image eg   import numpy as np import cv2  gray   cv2 imread  C  Python34 images 2015-05-27-191152 jpg  0

User · Answer

This code  for those who are experiencing the same problem trying to accessing the camera could be written with a safety check   if ret is True     gray   cv2 cvtColor frame  cv2 COLOR BGR2GRAY  else     continue   OR  in case you want to close the camera  discontinue  if there will be some problem with the frame itself   if ret is True     gray   cv2 cvtColor frame  cv2 COLOR BGR2GRAY  else     break   For reference https   github com HackerShackOfficial AI-Smart-Mirror issues 36

User · Answer

Please Set As Below  img   cv2 imread  2015-05-27-191152 jpg  1         Change Flag As 1 For Color Image                                                   or O for Gray Image So It image is                                                    already gray

User · Answer

In my case the error got resolved by migrating to OpenCV 4 0  or higher

User · Answer

I ve had this error message show up  for completely unrelated reasons to the flags 0 or 1 mentionned in the other answers  You might be seeing it too because cv2 imread will not error out if the path string you pass it is not an image   In  1   import cv2         img   cv2 imread  asdfasdf      This is clearly not an image file         gray   cv2 cvtColor img  cv2 COLOR BGR2GRAY           OpenCV Error  Assertion failed  scn    3    scn    4  in cv  cvtColor  file C  projects opencv-python opencv modules imgproc src color cpp  line 10638 --------------------------------------------------------------------------- error                                     Traceback  most recent call last   lt ipython-input-4-19408d38116b gt  in  lt module gt          1 import cv2       2 img   cv2 imread  asdfasdf      This is clearly not an image file ---- gt  3 gray   cv2 cvtColor img  cv2 COLOR BGR2GRAY   error  C  projects opencv-python opencv modules imgproc src color cpp 10638  error   -215  scn    3    scn    4 in function cv  cvtColor   So you re seeing a cvtColor failure when it s in fact a silent imread error  Keep that in mind next time you go wasting an hour of your life with that cryptic metaphor   Solution  You might need to check that your path string represents a valid file before passing it to cv2 imread     import os   def read img path          Given a path to an image file  returns a cv2 array      str - gt  np ndarray        if os path isfile path           return cv2 imread path      else          raise ValueError  Path provided is not a valid file      format path     path    2015-05-27-191152 jpg  img   read img path  gray   cv2 cvtColor img  cv2 COLOR BGR2GRAY    Written this way  your code will fail gracefully

User · Answer

2015-05-27-191152 jpg  lt  lt  Looking back at your image format  I occasionally confused between  png and  jpg and encountered the same error

User · Answer

Well I am having the same problem  but I am not taking input images instead getting video frames and the above solution did not work for that  The problem is in camera accessing  the camera of your laptop is still in use by your previous  code  you need to simply RESTART you KERNEL and it will work

User · Answer

I also found if your webcam didnt close right or something is using it  then CV2 will give this same error  I had to restart my pc to get it to work again

User · Answer

cv2 error   home arthurckl Desktop opencv-3 0 0-rc1 modules imgproc src color cpp 7564  error   -215  scn    3    scn    4 in function cvtColor   The above error is the result of an invalid image name or if the file does not exists in the local directory   img   cv2 imread  2015-05-27-191152 jpg  0  gray   cv2 cvtColor img  cv2 COLOR BGR2GRAY    Also if you are using the 2nd argument of cv2 imread   as  0   then it is already converted into a grayscaled image   The difference between converting the image by passing 0 as parameter and applying the following    img   cv2 cvtCOLOR img  cv2 COLOR BGR2GRAY     is that  in the case img   cv2 cvtCOLOR img  cv2 COLOR BGR2GRAY   the images are 8uC1 and 32sC1 type images

User · Answer

The simplest solution for removing that error was running the command   cap release   cv2 closeAllWindows     That worked for me and also sometimes restarting the kernel was required because of old processes running in the background   If the image isn t in the working directory then also it wont be working for that try to place the image file in pwd in the same folder as there is code else provide the full path to the image file or folder   To avoid this problem in future try to code with exceptional handling  so that if incorrect termination happens for some random reason the capturing device would get released after the program gets over

[python] open cv error: (-215) scn == 3 || scn == 4 in function cvtColor

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