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!

Answer 1

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() 

Answer 2

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