Converting Numpy Array to OpenCV Array

Question

I m trying to convert a 2D Numpy array  representing a black-and-white image  into a 3-channel OpenCV array  i e  an RGB image    Based on code samples and the docs I m attempting to do this via Python like   import numpy as np  cv vis   np zeros  384  836   np uint32  h w   vis shape vis2   cv CreateMat h  w  cv CV 32FC3  cv CvtColor vis  vis2  cv CV GRAY2BGR    However  the call to CvtColor   is throwing the following cpp-level Exception   OpenCV Error  Image step is wrong    in cvSetData  file  build buildd opencv-2 1 0 src cxcore cxarray cpp  line 902 terminate called after throwing an instance of  cv  Exception    what      build buildd opencv-2 1 0 src cxcore cxarray cpp 902  error   -13   in function cvSetData  Aborted   What am I doing wrong

User · Answer

The simplest solution would be to use Pillow lib   from PIL import Image  image   Image fromarray  lt your numpy array gt  astype np uint8     And you can use it as an image

User · Answer

This is what worked for me         import cv2 import numpy as np   Created an image  really an ndarray  with three channels  new image   np ndarray  3  num rows  num cols   dtype int    Did manipulations for my project where my array values went way over 255  Eventually returned numbers to between 0 and 255   Converted the datatype to np uint8 new image   new image astype np uint8    Separated the channels in my new image new image red  new image green  new image blue   new image   Stacked the channels new rgb   np dstack  new image red  new image green  new image blue     Displayed the image cv2 imshow  WindowNameHere   new rgbrgb  cv2 waitKey 0

User · Answer

Your code can be fixed as follows   import numpy as np  cv vis   np zeros  384  836   np float32  h w   vis shape vis2   cv CreateMat h  w  cv CV 32FC3  vis0   cv fromarray vis  cv CvtColor vis0  vis2  cv CV GRAY2BGR    Short explanation    np uint32 data type is not supported by OpenCV  it supports uint8  int8  uint16  int16  int32  float32  float64  cv CvtColor can t handle numpy arrays so both arguments has to be converted to OpenCV type  cv fromarray do this conversion  Both arguments of cv CvtColor must have the same depth  So I ve changed source type to 32bit float to match the ddestination    Also I recommend you use newer version of OpenCV python API because it uses numpy arrays as primary data type   import numpy as np  cv2 vis   np zeros  384  836   np float32  vis2   cv2 cvtColor vis  cv2 COLOR GRAY2BGR

[python] Converting Numpy Array to OpenCV Array

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