My first steps into Ruby and OpenCV(on OSX)

I was writing some robotic code that will run on a mac mini, so I tryied on my macbook for the first time, ruby binding to opencv. It was a weird experience lol.

First, to install OpenCV, brew do the job:

$ brew tap homebrew/science
$ brew install opencv

after a while we see that instalation goes flawlessly:
/usr/local/Cellar/opencv/ 278 files, 35.6MB
and we have current version: That said, now install ruby gem:

$ gem install ruby-opencv -- --with-opencv-lib=/usr/local/Cellar/opencv/ \
                             --with-opencv-include=/usr/local/Cellar/opencv/ \

Fetching: ruby-opencv-0.0.18.gem (100%)
Building native extensions with: '--with-opencv-lib=/usr/local/Cellar/opencv/ --with-opencv-include=/usr/local/Cellar/opencv/ --with-opencv-include=/usr/local/Cellar/opencv/'
This could take a while...
Successfully installed ruby-opencv-0.0.18
Parsing documentation for ruby-opencv-0.0.18
Installing ri documentation for ruby-opencv-0.0.18
Done installing documentation for ruby-opencv after 7 seconds
1 gem installed

after that, time to code.

My first try, obviously, is to use HAAR cascade classifier to look for faces.

require "rubygems"
require "opencv"
include OpenCV

window ="grab da face!")
camera =
detector = CvHaarClassifierCascade::load('./haarcascade_frontalface_alt.xml')
loop {
  image = camera.query
  detector.detect_objects(image).each { |rect|
    image.rectangle! rect.top_left, rect.bottom_right, :color => CvColor::Blue
  } image
  break if GUI::wait_key(100)

It didn’t worked as ruby-opencv currently supports only older type format of trained data xml. To solve that, I grabed older version of haarcascade_frontalface_alt.xml from and it worked as expected.
Sometimes, OSX Facetime camera stop working, but is easy to fix, just run

sudo killall VDCAssistant

wait a little and voilá.

In the end, was a different experience, it worked but was way too slow. I’ll try to tweak a little but python version are way faster and I believe I’ll keep using it.