Build opencv_contrib with dnn module

Introduction

opencv_dnn module is placed in the secondary opencv_contrib repository, which isn't distributed in binary form, therefore you need to build it manually.

To do this you need to have installed: CMake, git, and build system (gcc with make for Linux or MS Visual Studio for Windows)

Steps

1. Make any directory, for example opencv_root
2. Clone opencv and opencv_contrib repos to the opencv_root. You can do it in terminal like here:

   cd opencv_root
   git clone https://github.com/opencv/opencv
   git clone https://github.com/opencv/opencv_contrib

3. Run [CMake-gui] and set source and build directories:
   • Set source code directory to opencv_root/opencv;
   • Set binaries directory, for example, to opencv_root/build_opencv. This directory will contain built libraries.
     
4. Configure opencv:
   • press Configure;
   • choose the preferred project generator (Makefiles for Linux, MS Visual Studio for Windows);
   • also you can set many opencv build options, for more details see Installation in Linux.
     
5. In the appeared list of build parameters find parameter OPENCV_EXTRA_MODULES_PATH and set it to the opencv_root/opencv_contrib.
   
6. Configure the project again, and set build options of dnn module:
   • BUILD_opencv_dnn parameter must exist and be checked.
   • dnn module covers waste part of Caffe framework functionality. However, to load Caffe networks libprotobuf is required. You you can uncheck BUILD_LIBPROTOBUF_FROM_SOURCES flag to try use protobuf installed in your system. Elsewise libpotobuf will be built from opencv sources.
   • You can additionally check opencv_dnn_BUILD_TORCH_IMPORTER parameter to build Torch7 importer. It allows you to use networks, generated by Torch7.nn module.
     
7. Press Configure and Generate.
   
8. Build the generated project:
   • If Makefiles generator on Unix was used, run the following in terminal:

     cd opencv_root/build_opencv
     make all

   • If MS Visual Studio generator was used, then open OpenCV.sln from opencv_root/build_opencv folder in the Visual Studio, and build it by choosing Build -> Build Solution menu or using F7 short-cut.
9. Now you can build own program by using libraries were built into opencv_root/build_opencv/lib. See the following tutorials to learn how to create a program using OpenCV:
   • Installation in Windows
   • Using OpenCV with gcc and CMake