Face Detector using OpenCV and C

Build a Face Detector on OS X Using OpenCV and C++

Building and using C++ libraries can be a daunting task, even more so for big libraries like OpenCV. This article should get you started with a minimal build of OpenCV and a sample application written in C++.

This application will get images from the webcam, draw rectangles around the faces in the images and show them to you on screen.


I've built this on a MacBook Pro running OS X El Capitan Version 10.11.1.

We'll be using the GNU C++ compiler (g++) from the command line. Note that you should still have Xcode installed (I have Xcode 7.1 installed).

Here's what you need to do :

  1. Get "OpenCV for Linux/Mac" from the OpenCV Downloads Page I got version 3.0.
  2. Extract the contents of the zip file from step 1 to a folder of your choosing (I chose ~/opencv-3.0.0).
  3. Get a binary distribution of Cmake from the Cmake Downloads Page I got cmake-3.4.0-Darwin-x86_64.dmg.
  4. Install Cmake.


    Building OpenCV

OpenCV uses CMake files to describe how the project needs to be built. CMake can transform these files into actual project settings (e.g. an Xcode project, Unix makefiles, a Visual Studio project, etc.) depending on the generator you choose.

First open CMake and a small window will pop-up that will let you choose your build options based on the CMakeList.txt files in the opencv source directory. First click on the Browse Source... button and choose the path to the opencv source folder (the folder you extracted the zip file to at step 2). Then click on the Browse Build... button and choose a path to a build folder, I'm going to create a new folder called build in the previously mentioned source folder.

If at any point you are prompted to choose a generator, pick Unix Makefiles. If the paths you chose were correct, after you click the Configure button, you should be looking at something like this :


For a somewhat minimal OpenCV build, make sure you only have the following options enabled :

  • BUILD_opencv_apps
  • BUILD_opencv_calib3d
  • BUILD_opencv_core
  • BUILD_opencv_features2d
  • BUILD_opencv_flann
  • BUILD_opencv_hal
  • BUILD_opencv_highgui
  • BUILD_opencv_imgcodecs
  • BUILD_opencv_imgproc
  • BUILD_opencv_ml
  • BUILD_opencv_objdetect
  • BUILD_opencv_photo
  • BUILD_opencv_python2
  • BUILD_opencv_shape
  • BUILD_opencv_stitching
  • BUILD_opencv_superres
  • BUILD_opencv_ts
  • BUILD_opencv_video
  • BUILD_opencv_videoio
  • BUILD_opencv_videostab
  • WITH_1394
  • WITH_V4L

You should disable the options that are not in the list, especially the BUILD_SHARED_LIBS one. Don't touch the options that are text fields unless you know what you're doing.

Most of these options you don't need for this particular exercise, but it will save you time by not having to rebuild OpenCV should you decide to try something else.

Once you have selected the settings above, click Generate. Now you can navigate to the build folder, I'll do so with cd ~/opencv-3.0.0/build/ and run make to build OpenCV.

    Installing OpenCV

If everything goes well, after the build finishes, run make install to add the OpenCV includes to the /usr/local/include folder and the libraries to the /usr/local/lib and /usr/local/share/OpenCV/3rdparty/lib folders.

After that's done, you should be able to build your own C++ applications that link against OpenCV.

    The Face Detector Application

Now let's try to build our first application with OpenCV

Here's the code and comments that explain how to do just that :

I saved this as main.cpp. To build it I used the following command :
Hopefully, no errors should occur.


Before running the application, you have to copy the lbpcascade_frontalface.xml next to the main file.  You can find this file in the OpenCV source folder under /data/lbpcascades/. You can also find some other cascades to detect eyes, cat faces, etc.

Now just run the ./main and enjoy!

APIs in Symfony2

Getting Started with Building APIs in Symfony2

Hello all you Interwebs friends! While we're passing through the shallow mists of time, REST is becoming more and more of a universal standard when building web applications. That said, here's a very brief tutorial on how to get started with building APIs in Symfony2.

Spoiler alert: the bits of code written below use FosUserBundle + Doctrine.

1. Generate a New Bundle

It's nice to keep your code neat and tidy, so ideally, you should create a separate bundle that will only store your API code, we can generically name ApiBundle.

2.  Versioning

This isn't by any means mandatory, but if you believe that your API endpoints will suffer major changes along the way, that cannot be predicted from the get go, it would be nice to version your code. This means that you would, initially, have a prefix in your endpoints, like: /v1/endpoint.json, and you'd increase that value each time a new version comes along. I'll describe how to actually create the first version (v1) of your API a little further down the line.

3. Install a Few Useful Bundles

  • FosRestBundle - this bundle will make our REST implementation a lot easier.

and then include FOSRestBundle in your AppKernel.php file:

  • JmsSerializerBundle - this will take care of the representation of our resources, converting objects into JSON.

and then include JMSSerializerBundle in your AppKernel.php:

4. Configurations

Configure the Response object to return JSON, as well as set a default format for our API calls. This can be achieved by adding the following code in app/config/config.yml:

5. Routing

I prefer using annotations as far as routes go, so all we need to do in this scenario would be to modify our API Controllers registration in /app/config/routing.yml. This registration should have already been created when you ran the generate bundle command. Now we'll only need to add our version to that registration. As far as the actual routes of each endpoint go, we'll be manually defining them later on, in each action's annotation.
At this point we're all set to start writing our first bit of code. First off, in our Controller namespace, we would want to create a new directory, called V1. This will hold all of our v1 API Controllers. Whenever we want to create a new version, we'll start from scratch by creating a V2 namespace and so on.

After that's done let's create an action that will GET a user (assuming we've previously created a User entity and populated it with users). This would look something like:
If we want to GET a list of all users, that's pretty straightforward as well:
With that done, when running a GET request on https://yourapp.com/api/v1/users/1.json, you should get a json response with that specific user object.

What about a POST request? Glad you asked! There are actually quite a few options to do that. One would be to get the request data yourself, validate it and create the new resource yourself. Another (simpler) option would be to use Symfony Forms which would handle all this for us.

The scenario here would be for us to add a new user resource into our database.

If you're also using FosUserBundle to manage your users, you can just use a similar RegistrationFormType:
Next, we'll want to actually create our addUserAction():
To make a request, you'll need to send the data as raw JSON, to our https://yourapp.com/api/v1/users/new.json POST endpoint:

And that's all there is to it.

We haven't covered the cases where you'd want Delete or Update a user yet. Updating resources through the REST standards can be done using either PUT or PATCH. The difference between them is that PUT will completely replace your resource, while PATCH will only, well, patch it... meaning that it will partially update your resource with the input it got from the API request.

Let's get to it then. We'll use the same form as before, and we'll try to only change (we'll use the PATCH verb for that) the email address, username and password of our previously created user:
The request body is the same as the one shown for the POST method, above. There are a few small differences in our edit action though. First off - we're telling our form to use the PATCH method. Second - we are handling the case where the user ID provided isn't found.

The Delete method is the easiest one yet. All we need to do is to find the user and remove it from our database. If no user is found, we'll throw a "user not found" error:

Related: Routing in Symfony2


Aaand we're done. We now have a fully working CRUD for our User Entity. Thanks for reading and please do share your opinions/suggestions in the comment section below.

What Nobody Tells You When You're a Junior Developer

Hooray! You've landed your dream job and you can now proudly call yourself a Junior Developer. The future looks nothing but bright and your awesome life story is underway. But now the hard part actually begins. Here's how you can stay on top of things with some useful tips I wish I knew when I was in your shoes as a junior developer.

Read more