Develop Reference

OpenCV has no drawKeypoints function

I'm using Python 3.7.1 and OpenCV 4.0.0
I'm just testing FAST algorithm with various configurations, and I have problems with the drawKeypoints function. In fact, I copied OPenCV tutorial code, just to realize that the function needs a third argument, the output image. After that, everything was working, and I commited to the repo.
Later on, I had to format my pc, and reinstall everything. Now, whenever I try to run that code, it complains about module 'cv2' has no attribute 'drawKeypoints'. Here is the most basic code I had running after the format.
import numpy as np
import cv2
import sys
img = cv2.imread(sys.argv[1], 0)
fast = cv2.FastFeatureDetector_create()
kp = fast.detect(img,None)
img2 = cv2.drawKeypoints(img, kp, None, color=(255,0,0))
cv2.imshow('Original',img)
cv2.imshow('Detected',img2)
cv2.waitKey(0)
cv2.destroyAllWindows()
I've been looking, and I have no clue about what could be wrong with this code.

It looks related to this bug which has a solution in the git repository (sources), but not necessarily is updated in the installation using pip. It was merged on Dec 11 2018, so for the time of this question it was probably not updated.
Maybe getting an updated wheel could solve the problem or you can build it yourself from sources. Here you can also see how this is generated (the one from pip install) and also offers you the tool to build your own opencv wheel.

Is there no more module cv for opencv python?

The solutions on this question do not work with the opencv python version 3.3.1. cv2.__version__ prints 3.3.1-dev, and even import cv2.cv returns the no module error.
On reading this answer it seems like both the cv2 and cv interfaces were maintained, at least for a while but that doesn't seem the case any more.
So...
Does the cv module exist any more?
If not, then from which opencv version was this lost? And where can we find old cv functions? For instance cv.StereoRectify
Thank you

In OpenCV 3.x cv was deprecated.
Some old cv modules can be found in cv2, as cv2.stereoRectify, others are not in opencv installation anymore due to legal concerns.
You may need to pip install opencv-contrib-python --user

It seems that the old cv module has been completely removed from OpenCV in version 3.
Old functions should have been ported to the current cv2 module. In your case, it seems cv.StereoRectify is now cv2.stereoRectify

cannot find reference for opencv functions in pycharm

I have opencv-python installed and the .pyd file is added in the site-packages and the DLLs. The code works with images. When I want to read, show, write an image it works. But I get a warning that the functions' references cannot be found in init.py . Due to this, I can not use the auto-complete feature. Could someone help me out? I am using opencv 3.4.0 and python 3.6.4 in pycharm. I downloaded opencv via pip in the command prompt.

The problem is caused by CV2 and how __init__.py does the imports. Just ignore the warnings the program will work all the same, or you can do an import with an alias like:
import cv2.cv2 as cv2
If you have a warning on it press Alt+Enter to install and fix it. Now you will have the code completion and no other warnings (about that) on the project.

Switching to an older version of opencv solved this problem for me.
Apparently pycharm sometime breaks depending on the version of opencv. For me, the newest version was, 4.6.X unstalling and installing 4.5.X did the trick.

I use python 3.10 and my newest version for opencv is 4.6.0.66 ,by changing opencv version to 4.5.5.62 and with an alias: import cv2.cv2 as cv2 my problem has solved.

Import cv2 as follows:
from cv2 import cv2

I installed version 4.5.5.64 and imported with an alias.
import cv2.cv2 as cvv2

I was using Python 3.10.2288.0 and OpenCV 1.6.0.66.
I resolved the issue by rolling back the OpenCV version to 4.5.5.62.

Alternative for PIL?

I want to use one of the newest versions of Python, (3.5+), and I need to import Image. I use:
from PIL import Image
except this returns an error. I don't have the error on my right now but the important part is there is a problem with PIL (I have already determined that from my Python Discord server)
Can I use pillow? I think I have that installed. I would try it but I want to know how (and if) it's applicable. Thanks

Can I use pillow?
Sure. pillow is a successor project of PIL, as development on the latter was last continued in 2011.
The first thing mentioned in the official pillow documentation is how to import the Image class.

Image library for Python 3

What is python-3 using instead of PIL for manipulating Images?

The "friendly PIL fork" Pillow works on Python 2 and 3. Check out the Github project for support matrix and so on.

Christoph Gohlke managed to build PIL (for Windows only) for python versions up to 3.3: http://www.lfd.uci.edu/~gohlke/pythonlibs/
I tried his version of PIL with Python 3.2, and image open/create/pixel manipulation/save all work.

Qt works very well with graphics. In my opinion it is more versatile than PIL.
You get all the features you want for graphics manipulation, but there's also vector graphics and even support for real printers. And all of that in one uniform API, QPainter.
To use Qt you need a Python binding for it: PySide or PyQt4.
They both support Python 3.
Here is a simple example that loads a JPG image, draws an antialiased circle of radius 10 at coordinates (20, 20) with the color of the pixel that was at those coordinates and saves the modified image as a PNG file:
from PySide.QtCore import *
from PySide.QtGui import *
app = QCoreApplication([])
img = QImage('input.jpg')
g = QPainter(img)
g.setRenderHint(QPainter.Antialiasing)
g.setBrush(QColor(img.pixel(20, 20)))
g.drawEllipse(QPoint(20, 20), 10, 10)
g.end()
img.save('output.png')
But please note that this solution is quite 'heavyweight', because Qt is a large framework for making GUI applications.

As of March 30, 2012, I have tried and failed to get the sloonz fork on GitHub to open images. I got it to compile ok, but it didn't actually work. I also tried building gohlke's library, and it compiled also but failed to open any images. Someone mentioned PythonMagick above, but it only compiles on Windows. See PythonMagick on the wxPython wiki.
PIL was last updated in 2009, and while it's website says they are working on a Python 3 port, it's been 3 years, and the mailing list has gone cold.
To solve my Python 3 image manipulation problem, I am using subprocess.call() to execute ImageMagick shell commands. This method works.
See the subprocess module documentation.

You can use my package mahotas on Python 3. It is numpy-based rather than PIL based.

You want the Pillow library, here is how to install it on Python 3:
pip3 install Pillow
If that does not work for you (it should), try normal pip:
pip install Pillow

Depending on what is needed, scikit-image may be the best choice, with manipulations going way beyond PIL and the current version of Pillow. Very well-maintained, at least as much as Pillow. Also, the underlying data structures are from Numpy and Scipy, which makes its code incredibly interoperable. Examples that pillow can't handle:
You can see its power in the gallery. This paper provides a great intro to it. Good luck!

If you are on Python3 you can also use the library PILasOPENCV which works in Python 2 and 3. Function api calls are the same as in PIL or pillow but internally it works with OpenCV and numpy to load, save and manipulate images. Have a look at https://github.com/bunkahle/PILasOPENCV or install it with pip install PILasOPENCV. Not all PIL functions have been simulated but the most common functions work.