Using OpenCv contrib modules for android

Question

Is there a way to use opencv contrib modules in android ? I am specifically using text module. Is there a android lib for these modules. I have my code working on desktop and i m trying to migrate my codes to android. Any insight would be gr8.

Answer 1

I was having issues figuring out solutions to these problems as well. I thought I would find a relevant question out there and put a response in for the community in case others are also looking for solutions to a problem similar to this one and mine. Compilation was done on a Macbook Retina 13".

The instructions provided are somewhat incomplete and there are additional steps that will be needed to get to a final product.

At the start you will follow the standard procedure as outlined online

$ cd <opecv_directory>
$ mkdir build
$ cd <opencv_build_directory>
$ cmake -D OPENCV_EXTRA_MODULES_PATH=<opencv_contrib>/modules <opencv_source_directory>
$ make -j5
$ make install

In addition to this, you may run across an error or two. I needed to install some missing components in order to get past things that were missing but this may differ for you (I researched errors and understood that I needed additional components)

brew install ninja
brew install oxygen
brew install ant

I also ran into an error with one module requesting the need for the following declared in the source code (or with compiler flags):

#define SOLARIS_64BIT_ENABLED

Another thing you can do is remove other modules in the contrib folder you may not be interested in during compilation. Just include the modules you want and hopefully those ones are good. I did this simply by removing one or two from the /modules folder and then reran the python script.

A final python script was needed to run the build. I created a directory alongside the main source tree and contrib folder.

OpenCVSource
  -> opencv
  -> opencv_contrib
  -> android_opencv_build

The call below was made from the directory where I want the build to be taking place from, so I changed to the directory The call was the following:

python ../opencv/platforms/android/build_sdk.py --extra_modules_path ../opencv_contrib/modules --ndk_path <your-path-to-ndk-top-level-folder> --sdk_path <your-path-to-sdk-top-level-folder> ./ ../opencv

This only builds the .so files that are necessary for using the library, but it doesn't build the .jar file that you will need to use the new binaries. In order to do that navigate to your build folder (mine as seen is in android_opencv_build/OpenCV-android-sdk)

Load this project into Eclipse in the standard manner with the import existing Android project into workspace. You really only need the /sdk project but feel free to load samples as well if desired. Then build the project. You may need to alter the target build to support the new Camera APIs for a successful build; in my case changing the target to API level 21.

You will then find the .jar file in the /bin directory of the project. The .jar and the .so files found in android_opencv_build/OpenCV-android-sdk/sdk/native/jni/ contain the necessary .so files that you will need to include in your projects /lib folder alongside this jar.

Now you should have everything that you need. Since we are working with contrib modules (or not if you are building it for other reasons), it is possible that you will run across other errors in the build process that are not quite stable and will need some attention. This cannot be helped but people can feel free to add comments to other peoples solutions and this post to aide them in resolving them if they have found a solution.