Installing OpenCV for Python on Mac Lion

Like previous installs of other command-line tools like FFMPEG, the frustration often does not seem worth the trouble.  Esoteric errors are near impossible to parse and files are installed in odd places (odd to me, at least).  Below are the steps I used to install the OpenCV library (blob detection, facial tracking, etc etc) for use with Python on my Mac, running 10.7.4 (Lion).

Much of this was pulled from a StackOverflow post ( but the suggestions would have been less helpful had they not be corroborated by several other posts with similar suggestions.  That said, this was the only guide I could find that worked well for me (thanks!).

  1. Install MacPorts (download here)
    If you haven’t already – this makes installation mucheasier; test the install by typing the following into the Terminal:

    If you don’t get an error, it installed correctly
  2. Check your Python version
    If you have Lion, you are likely running Python 2.7 – to double-check, type:

    And see what version comes up.  The problem installing OpenCV for Python seems to be a conflict between what version of Python MacPorts assumes and what you’re really running.  To be sure you are using 2.7, type this into the Terminal:
  3. Install NumPy
    Not sure why this is necessary, but appears to be (NumPydoes 2d array processing, so that’s likely the reason); type the following:
  4. Install OpenCV
    We’re ready!  Type the following and be prepared to wait – OpenCV is quite large and takes a while to download and get set up.  If you’ve already installed it in another location (I had) it appears that MacPorts just links it – nice!  Type:
  5. Test
    In the Terminal, type the following to enter Python:

    Then, to test OpenCV, type:

    If you don’t get an error, you’re good!  To exit Python, type:

Some of the suggestions I found say that you need to do some further profile editing and other (weird) stuff – I didn’t need to, but if you have problems it might be worth a try.

To further test the library, try this simple example that converts an image from one file format to another.  I wrote this in TextWrangler, saved the file, and ran it using the #! > Run in Terminal… command (requires the command-line tools to be installed.

The new file should be generated and you’re good to go!

Thoughts, suggestions, or problems?  Please send me an email: mail [at] jeffreythompson [dot] org