T04-04 OpenCV: Use Numpy operations in lieu of OpenCV built-in functionality?[138756758]

[sangto]

OpenCV, like PIL, has a lot of built-in functionality that can be done just as easily with Numpy. I think this would be a better way to do things with the students, so that we scaffold on the work we’ve already done with them.

For example, suppose we’ve loaded the car.jpg image as “image” with cv. Then “image” gets treated as a Numpy array. Hence, to convert RGB to BGR we could simply do this:

image=image[:,:,::-1] #reverse the order of B,G,R
or this:
image[:,:,[0,2]]=image[:,:,[2,0]] #swap B and R

Horizontal and vertical flips are similar:

image=image[::-1,:,:] #Flip across horizontal axis
and
image=image[:,::-1,:] #Flip across vertical axis

Here’s a vertical compression by a factor of 2:
image=image[::2,:,:]