Stepping up the game : Building OpenCV with OpenMP

OpenCV API has been a choice for Image Processing over MATLAB for quite a while now especially on an SoC like Raspberry Pi 3.

However I always had an inquisitive concern (too fancy?) whenever I ran an OpenCV project (as in my previous project for Real-Time Face Recognition System ) that when it seemed that the CPU is doing the best it can, the CPU usage graph never went above 25%.

Since Raspberry Pi has a Quad-Cored BCM 2837 , this meant that the program is using a single core for all the tasks. The fact that my applications are unable to exploit the resources that are available posed a problem to be solved; OpenMP to the rescue.

OpenMP API 

Why OpenMP :

Because it is simple and since Raspberry Pi has no significant GPU (for High Performance Computing) which puts OpenCL out of question and no Nvidia tag anywhere puts CUDA out of the picture too. OpenCL can be implemented on a CPU too but the lead time and the overhead will be too much for now.

OpenMP API is designed for multi-processor/core, shared memory machines and has a compiler directive based usage which though simpler to implement does require careful considerations. A thoughtless "#Parallel For" loop can significantly back fire and cause things to break.

A number of tutorials and documentations for OpenMP API are available.Two of those:  here and here!

Building OpenCV with OpenMP requires a simple addition at the building process:

 cmake -D CMAKE_BUILD_TYPE=RELEASE -D WITH_OPENMP=ON -D CMAKE_INSTALL_PREFIX=/usr/local ..  

I also used my tried and tested method of building extra modules that has never failed me since its discovery.
The building process starts and completes as it should with the following OpenMP tag somewhere in the entire log:

  Parallel framework:      OpenMP  

The OpenMP and OpenCV seem like a good pair to work with on Raspberry Pi.
Will post an update to my inquisitive concern after I get the OpenMP implementation done.
Lot of directives to add.

Update [27/Aug/17]: Added follow up post : Multicore Processing using OpenMP

There are no wrong turnings. Only paths we had not known we were meant to walk.

Peace Out.

Stats:
Ubuntu 16.04
OpenCV 3.2.0
GCC 5.4.0