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Month: September 2013

OpenCV for Android

Why another tutorial for OpenCV for Android? I followed a tutorial from the OpenCV official website. It was disappointing. It turned out there are many problems during installation and building examples in my Mac OS X system.

My Android SDK version is 4.2.2 (API 17) with Android Development Tools (ADT) for its IDE. I believe this tutorial works as well with Android 4.3 (API 18) in Mac OS X.

Here is a list of steps to follow to get OpenCV for Android ready for you.

Download OpenCV for Android

  1. Download OpenCV for Android from http://opencv.org/downloads.html. You can find an Android version from the web. As I am writing this, the latest version is 2.4.6.
  2. Unzip the zip file and you will see a folder.
  3. Place the folder into a proper folder. In my case, I created a folder in my Documents and named it as work. And copy the OpenCV folder into the new folder.
  4. This is it for now until we build the libraries and samples.

Download Android NDK

You may find an NDK Plugins item from the menu Help – Install New Software. I tried this. But it shows the following error message.

Cannot complete the request. See the error log for details.
“Android Native Development Tools” will be ignored because it is already installed.

So I went to the Android NDK webpage and found a package. It seems we need to install this manually.

  1. Download a package from http://developer.android.com/tools/sdk/ndk/index.html. You can find two packages for each platform. Just select the first package which is a current and recommended toolchain for the NDK.
  2. Unzip it.
  3. Find a folder named “android-ndk-<version>.”
  4. Place this folder into the “work” folder. See the ‘Download OpenCV for Android’ section for more detail about the “work” folder.

Build OpenCV Library and Samples

Now we are kind of ready to build OpenCV Samples because we have to take a few more steps after importing Android projects from the OpenCV folder to your ADT’s workspace.

There is an NDK item in the Preferences of ADT under the Android section. It looks like we have to put NDK folder into the blank. But this is useless at least for the OpenCV samples. So you may ignore this NDK item in the Preferences.

  1. Select File – Import – Android – Existing Android Code into Workspace.
  2. You will see the ‘Import Project’ dialog.
  3. Choose ‘Root Directory’ by clicking the ‘Browse…’ button. The directory is the top folder of the OpenCV folder that you placed in the section ‘Download OpenCV for Android.’
  4. Now you can see five samples and three tutorials and one library. Select all the projects. If you want to use only one sample or tutorial, please don’t forget to select the project “sdk/java – OpenCV Library.” Then Click the ‘Finish’ button.
  5. If you want to maintain all original samples in the folder, you can check the “Copy projects into workspace” checkbox. This will copy all source code into your workspace.
  6. Some projects will show compile errors. According to OpenCV website tutorials, the errors will be shown only on a non-Windows operating systems. Anyway, I am using a Mac. So I see the errors. The remedy in the web http://docs.opencv.org/doc/tutorials/introduction/android_binary_package/O4A_SDK.html didn’t work for me. Here is what I did.
  7. First of all, NDKROOT is not defined in my system. Add NDKROOT with the value of the actual android-ndk folder that you placed in the section ‘Download Android NDK.’ This should be done all the complaining projects with errors.
    1. Go to Properties (@I) of each project. Note that this is NOT ‘Preferences.’ Select one project and right click. Find the Properties item in the bottom of the context menu.
    2. Find C/C++ Build – Environment.
    3. Add a variable. Name it NDKROOT and put a value with your android-ndk folder.
  8. Then go back the C/C++ Build item in the Properties. You can find ‘Build command:” Its corresponding text input box has either ${NDKROOT}/ndk-build.cmd or “${NDKROOT}/ndk-build.cmd” (Note that the quotation marks!). Remove ‘.cmd’ and the quotation marks if it has. I just want ${NDKROOT}/ndk-build in the text input box.

OpenCV Manager

If your Android phone does not have OpenCV Manager, you should download it from https://play.google.com/store/apps/details?id=org.opencv.engine&hl=en.

That’s it. Enjoy OpenCV for Android!!!

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