How to convert a python numpy array to an RGB image with Opencv 2 4

Question

I have searched for similar questions  but haven t found anything helpful as most solutions use older versions of OpenCV    I have a 3D numpy array  and I would like to display and or save it as a BGR image using OpenCV  cv2     As a short example  suppose I had   import numpy  cv2 b   numpy zeros  5 5 3    b     0    numpy ones  5 5   64 b     1    numpy ones  5 5   128 b     2    numpy ones  5 5   192   What I would like to do is save and display b as a color image similar to   cv2 imwrite  color img jpg   b  cv2 imshow  Color image   b  cv2 waitKey 0  cv2 destroyAllWindows     This doesn t work  presumably because the data type of b isn t correct  but after substantial searching  I can t figure out how to change it to the correct one  If you can offer any pointers  it would be greatly appreciated

User · Answer

The images c  d  e   and f in the following show colorspace conversion they also happen to be numpy arrays  lt type  numpy ndarray  gt    import numpy  cv2 def show pic p               use esc to see the results            print type p           cv2 imshow  Color image   p          while True              k   cv2 waitKey 0   amp  0xFF             if k    27  break          return         cv2 destroyAllWindows    b   numpy zeros  200 200 3    b     0    numpy ones  200 200   255 b     1    numpy ones  200 200   255 b     2    numpy ones  200 200   0 cv2 imwrite  color img jpg   b    c   cv2 imread  color img jpg   1  c   cv2 cvtColor c  cv2 COLOR BGR2RGB   d   cv2 imread  color img jpg   1  d   cv2 cvtColor c  cv2 COLOR RGB2BGR   e   cv2 imread  color img jpg   -1  e   cv2 cvtColor c  cv2 COLOR BGR2RGB   f   cv2 imread  color img jpg   -1  f   cv2 cvtColor c  cv2 COLOR RGB2BGR    pictures    d  c  f  e   for p in pictures          show pic p    show the matrix print c  print c shape    See here for more info  http   docs opencv org modules imgproc doc miscellaneous transformations html cvtcolor  OR you could   img   numpy zeros  200 200 3    img     0    numpy ones  200 200   255 img     1    numpy ones  200 200   255 img     2    numpy ones  200 200   0  r g b   cv2 split img  img bgr   cv2 merge  b g r

User · Answer

If anyone else simply wants to display a black image as a background  here e g  for 500x500 px   import cv2 import numpy as np  black screen    np zeros  500 500 3   cv2 imshow  Simple black   black screen  cv2 waitKey 0

User · Answer

You don t need to convert NumPy array to Mat because OpenCV cv2 module can accept NumPyarray  The only thing you need to care for is that  0 1  is mapped to  0 255  and any value bigger than 1 in NumPy array is equal to 255  So you should divide by 255 in your code  as shown below   img   numpy zeros  5 5 3    img     0    numpy ones  5 5   64 255 0 img     1    numpy ones  5 5   128 255 0 img     2    numpy ones  5 5   192 255 0  cv2 imwrite  color img jpg   img  cv2 imshow  image   img  cv2 waitKey

User · Answer

You are looking for scipy misc toimage   import scipy misc rgb   scipy misc toimage np array    It seems to be also in scipy 1 0  but has a deprecation warning  Instead  you can use pillow and PIL Image fromarray

User · Answer

This is due to the fact that cv2 uses the type  quot uint8 quot  from numpy  Therefore  you should define the type when creating the array  Something like the following  import numpy import cv2  b   numpy zeros  5 5 3   dtype numpy uint8  b     0    numpy ones  5 5   64 b     1    numpy ones  5 5   128 b     2    numpy ones  5 5   192

User · Answer

The size of your image is not sufficient to see in a naked eye  So please try to use atleast 50x50   import cv2 as cv import numpy as np  black screen   np zeros  50 50 3    black screen       2    np ones  50 50   64 255 0 cv imshow  Simple black   black screen  cv waitKey 0  cv displayAllWindows

[python] How to convert a python numpy array to an RGB image with Opencv 2.4?

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