Officially, OpenCV releases two types of Python interfaces,
I started working on
cv. In this, all OpenCV data types are preserved as such. For example, when loaded, images are of format
cvMat, same as in C++.
For array operations, there are several functions like
cvGet2D, etc. And some discussions say, they are slower.
For imageROI, you need special functions like
If you find contours,
cvSeq structures are returned which is not so good to work with compared to Python lists or NumPy arrays.
(And I think, soon its development will be stopped. Earlier, there was only
cv. Later, OpenCV came with both
cv2. Now, there in the latest releases, there is only the
cv2 module, and
cv is a subclass inside
cv2. You need to call
import cv2.cv as cv to access it.)
And the latest one is
cv2. In this, everything is returned as
NumPy objects like
native Python objects like
dictionary, etc. So due to this NumPy support, you can do any numpy operation here.
NumPy is a highly stable and fast array processing library.
For example, if you load an image, an
ndarray is returned.
array[i,j] gives you the pixel value at (i,j) position.
Also, for imageROI, array slicing can be used like
ROI=array[c1:c2,r1:r2]. No need of separate functions.
To add two images, there isn't a need to call any function, just do
res = img1+img2. (But NumPy addition is a modulo operation for uint8 arrays like images. See the article Difference between Matrix Arithmetic in OpenCV and Numpy to know more.
Contours returned are lists of Numpy arrays. You can find a detailed discussion about Contours in Contours - 1 : Getting Started.
In short, with cv2 everything is simplified and pretty fast.
A simple discussion on how NumPy speed up
cv2 is in Stack Overflow question Performance comparison of OpenCV-Python interfaces, cv and cv2.
I don't know much about this since I haven't used it. But it seems to have stopped further development.
I think it would be better to stick on to official libraries.
In short, I would recommend you to use cv2!
EDIT: You can see installation procedure for the
cv2 module in Install OpenCV in Windows for Python.