RICOH Blog Post: "Running OpenCV in Your RICOH THETA"

This article was originally published in Japanese by roohii_3 on the Qiita blogging site.

Currently (Feb 4) there is no repo publicly available. The first person in the community who builds this code and posts a working apk to GitHub, we will give out a Free Unity Virtual Reality Course ($79 value). Please help out the community!

UPDATE: Woohoo, thank you @Kasper ! We got the repo (Feb 9) from community member @Kasper and have built and used it ourselves. Nice work! Details in replies below this main post.

I attempted to run OpenCV inside a RICOH THETA. I hope this will be a good reference for people interested in building an app using OpenCV with Android Studio + NDK (ndk-build).


Hello, this is @roohii_3 from RICOH.

RICHO THETA is our company’s 360 degree camera. The newest version (as of December 2018) THETA V has an Android based OS. THETA can be customized the same way Android apps are. This customization is called “plug-ins."

By combining OpenCV + the Cloud, using a THETA plug-in, it might be possible to setup an IoT sort of use, like recognizing an object and shooting an image, then uploading it up to the Cloud. So, let’s start up OpenCV using a THETA plug-in.

Development Environment

  • OpenCV Android pack ver. 3.4.4
  • Android Studio ver. 3.2.1
  • JDK ver. 1.8.0_191
  • NDK ver. 18.1.5063045
  • gradle ver. 4.6
  • RICOH THETA V Firmware ver. 2.50.1
    (Android ver. 7.1.2 / API level 26)


OpenCV Android pack

  1. Download the newest version of “Android pack” from the OpenCV Releases page.

  2. After unzipping the downloaded file, save it to any convenient location. I renamed ”OpenCV-android-sdk” to ”OpenCV-3.4.4-android-sdk”, and saved it here:


Android Development Environment

Android Studio

From Android Developers, download and install Android Studio.

Android SDK・Tools

  1. Open ”Tools > SDK Manager” from the Android Studio menu.

  2. From the ”SDK Platforms” tab, check the necessary boxes depending on the Android version.

  1. In the ”SDK Tools” tab, if these boxes are not checked, check them.
  • Android SDK Build-Tools
  • Android SDK Platform-Tools
  • Android SDK Tools
  • Google USB Driver
  • NDK
  1. Click "OK”


From the link below, download and install ”Java SE Developer Kit 8”


When using THETA, reference the links below to set it to developer mode.

OpenCV for Android

According to "Android Development with OpenCV” in the OpenCV official docs, there are number of ways to use OpenCV with Android.

  1. Using with Java

    1.1 Using OpenCV Manager

    1.2 Using Static Linked Library

  2. Using with C/C++ and NDK

  • It seems that there are two ways to do builds: “CMake” or “ndk-build”

It appears that “1.1 Using OpenCV Manager” is recommended in the OpenCV official docs. (Footnote 1: ”Using async initialization is a recommended way for application development. It uses the OpenCV Manager to access OpenCV libraries externally installed in the target system.”) (Footnote 2: For OpenCV Manager, details are in [Android OpenCV Manager] The document is ver.2.4, so the information might be old.). However, because THETA is not always connected to network, OpenCV Manager features cannot be fully taken advantage of.

Therefore, that means using 1.2 or 2. This time “2. Using with C/C++ and NDK" will be used. “ndk-build” is used for the build.

Preparing the Project File・NDK Build Environment

  1. Creating a new Android Studio project

Open Android Studio, select "File > New Project”. Follow the screen and create "Empty Activity”.

  • No need to check "Include C++ support”. When this is checked, it appears that CMakeList.txt will be created. However, this time ndk-build is used, so there is no need.
  1. Creating the build file

Create a “jni” directory under the “app” directory, and create "” and “”.


For each file, input the following:


  • In the include on Line 7, add the path for “” in the OpenCV Android pack.

  • In LOCAL_MODULE, create an arbitrary name (the library name generated by NDK).

  • In LOCAL_SRC_FILES, create source name of C/C+ (native code).
    ※ If there are multiple native codes, it appears a space is used to indicate the difference. (Footnote 3:  |  Android NDK  |  Android Developers)

    LOCAL_PATH := $(call my-dir)

    include $(CLEAR_VARS)

    include C:\opencv\OpenCV-3.4.4-android-sdk\sdk\native\jni\

    LOCAL_MODULE := opencvsample
    LOCAL_SRC_FILES := sample.cpp


  • For APP_ABI,create suitable one depending on your platform.

    APP_STL := c++_static
    APP_CPPFLAGS := -frtti -fexceptions
    APP_ABI := armeabi-v7a

  1. Copying the OpenCV library (.so file)

Create a “jniLibs” directory under the “app” directory, then copy and paste the OpenCV library (.so file). Copy and paste the necessary library file into each directory, depending on your platform.

What to copy C:/(Where OpenCV Android pack is located)/sdk/native/libs/armeabi-v7a
Where to copy to C:/(Where the Project File is located)/app/jniLibs/armeabi-v7a


  1. Editing build.gradle

Open build.gradle(Module:app) and add NDK configuration as below.

• For moduleName configure the name of LOCAL_MODULE in “” by adding “lib” at the beginning of the name.

• Set the value of abiFilters to the appropriate amount depending on your platform.

android {
    defaultConfig {
        ndk {
            moduleName "libopencvsample"
            abiFilters 'armeabi-v7a'

When “Sync Now” appears in upper portion of the editor window, click it.

  1. Configuring the Build System

Right click “app” in the project tree, and select "Link C++ Project with Gradle”

Specify the path of “ndk-build” in an open window of the Build System, set “” in the path for Project Path, and click OK.



Here, we will open “lena.jpg” that is placed on “drawable," start up OpenCV in Native code, change the color space from RGB to BGR, and display that in ImageView.

Here, we open “lena.jpg” which has been placed in “drawable”, move OpenCV in Native code, convert color space from RGB to BGR, and display it on ImageView.


TextView, which displays the version, and ImageView, which displays the post treatment image, are configured.

<?xml version="1.0" encoding="utf-8"?>
< xmlns:android=""

        app:layout_constraintRight_toRightOf="parent" />



Java Code

With “”, add “lib” to the beginning of the library name, which was configured in LOCAL_MODULE, and read with System.loadLibrary().

The native code function is declared public native String version();

package com.theta360.opencvsample;

import android.os.Bundle;
import android.widget.ImageView;
import android.widget.TextView;

import java.nio.ByteBuffer;

public class MainActivity extends AppCompatActivity {

    // load native library
    static {

    private TextView mTextView;
    private ImageView mImageView;

    protected void onCreate(Bundle savedInstanceState) {

        // OpenCV version
        mTextView = (TextView) findViewById(;
        mTextView.setText("OpenCV version: " + version());

        // load the picture from the drawable resource
        Bitmap img = BitmapFactory.decodeResource(getResources(), R.drawable.lena);

        // get the byte array from the Bitmap instance
        ByteBuffer byteBuffer = ByteBuffer.allocate(img.getByteCount());

        // call the process from the native library
        byte[] dst = rgba2bgra(img.getWidth(), img.getHeight(), byteBuffer.array());

        // set the output image on an ImageView
        Bitmap bmp = Bitmap.createBitmap(img.getWidth(), img.getHeight(), Bitmap.Config.ARGB_8888);
        mImageView = (ImageView) findViewById(;

    // native functions
    public native String version();
    public native byte[] rgba2bgra(int width, int height, byte[] src);

Native code

OpenCV processing will be done in C/C++.

Under "app > jni”, create a C/C++ file with any name.

In LOCAL_SRC_FILES of “”, set the file name that you just created.


There seems to be unique rules for functions used in Java ↔ Native(C/C++). It’s defined here:

JNIEXPORT [return value format] JNICALL Java_[relative path from the top source directory for Java source]_[Java class name of caller origin]_[function name](JNIEnv *, jobject, [argument], ...))

It seems both the returned value and argument forms used are also unique.

For details, please refer to JNI Types and Data Structures.

#include <jni.h>
#include <string>
#include <opencv2/core.hpp>
#include <cv.hpp>

extern "C"
            JNIEnv *env,
            jobject) {
        std::string version = cv::getVersionString();
        return env->NewStringUTF(version.c_str());

    JNIEXPORT jbyteArray
    JNICALL Java_com_theta360_opencvsample_MainActivity_rgba2bgra
                    JNIEnv *env,
                    jobject obj,
                    jint w,
                    jint h,
                    jbyteArray src
            ) {
        // Obtaining element row
        // Need to release at the end
        jbyte *p_src = env->GetByteArrayElements(src, NULL);
        if (p_src == NULL) {
            return NULL;

        // Convert arrangement to cv::Mat
        cv::Mat m_src(h, w, CV_8UC4, (u_char *) p_src);
        cv::Mat m_dst(h, w, CV_8UC4);

        // OpenCV process
        cv::cvtColor(m_src, m_dst, CV_RGBA2BGRA);

        // Pick out arrangement from cv::Mat
        u_char *p_dst =;

        // Assign element for return value use
        jbyteArray dst = env->NewByteArray(w * h * 4);
        if (dst == NULL) {
            env->ReleaseByteArrayElements(src, p_src, 0);
            return NULL;
        env->SetByteArrayRegion(dst, 0, w * h * 4, (jbyte *) p_dst);

        // release
        env->ReleaseByteArrayElements(src, p_src, 0);

        return dst;


When executed, the following will be displayed.

*THETA does not have a display, so Vysor is used.


Next time around, I would like to make something that more fully takes advantage of the characteristics of 360 degree images, since this exercise was just to check the operation of OpenCV running inside a THETA. When I make more progess, I will post the results.

About the RICOH THETA Partner Program

If you are interested in THETA plug-in development, please register for the partner program!

Please be aware that the THETA with its serial number registered with the program will no longer be eligible for standard end-user support.

For detailed information regarding partner program please see here.

The registration form is here.

Extra Resources

If you’ve registered with the Partner Program (putting your THETA in developer mode) and have sent in your serial number (allowing you to develop and upload plug-ins), I’ve got some super useful resources for you! has pulled together a Top 10 THETA Developer Tips, pulling together feedback from developers, saving you time. We also have some choice apks that you can load immediately and try out with documentation and source code.

Work with speaker volume, record audio files, build a Web GUI for your THETA and lots more!

Send us your contact info and you’ll get an email will all the download links.

Hi jcasman,

I got it up and running. I’ve put a github repo up on have a look. I hope it works on your side.

Next some serious opencv stuff. Hope to have something for you soon!

thanx for all the help!


Wow, great contribution. I compiled your repo, installed it and ran OpenCV!




Test with RICOH THETA Image



Processed with OpenCV Plug-in Internal to THETA

Original 2


Processed with OpenCV Plug-in Internal to THETA

Original 3


Plug-in Test 3

Changing Image Orientation

In sample.cpp

Vertical Flip

    cv::flip(m_src, m_dst, 0);

Horizontal Flip

        cv::flip(m_src, m_dst, +1);




Update 2/12/2019: I’ve asked the developer for an example of using the last image taken from the THETA camera. @Kasper, are you able to use the image from the THETA storage? Right now, the image is in Android resources/drawables. I’d like to pull it from camera storage DCIM/RICOH100 and then save the processed image back in there.

    Bitmap img = BitmapFactory.decodeResource(getResources(), R.drawable.lena);

There’s a tutorial that appears to be relevant here:

Feb 16, 2019

Can now read in image from THETA storage.


BitmapFactory.Options options = new BitmapFactory.Options();

 options.inSampleSize = 4;

String photoPath = Environment.getExternalStorageDirectory() + "/DCIM/100RICOH/" + "R0010275.JPG";

Bitmap imgTheta = BitmapFactory.decodeFile(photoPath, options);
ByteBuffer byteBufferTheta = ByteBuffer.allocate(imgTheta.getByteCount());
byte[] dstTheta = rgba2bgra(imgTheta.getWidth(), imgTheta.getHeight(), byteBufferTheta.array());

Bitmap bmpTheta = Bitmap.createBitmap(imgTheta.getWidth(), imgTheta.getHeight(), Bitmap.Config.ARGB_8888);

In AndroidManifest.xml

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Forked the repo from @Kasper and added a branch camera_file. Just getting started on this and not getting the last image taken yet.

1 Like

Hee @codetricity,

great addition! I’ve been playing around a bit more with the NDK and the C++ side but ran into some problems with using opencv to save files in cpp. (imread needs to be recompiled if I understand it correctly.)

So I decided to look a bit more into integrating opencv directly in Java. After some trail and error and the I finally got it to run.

If you would like to I can write a tutorial about it. Would that be interesting?

I continued and started building on my HDR to EXR app.
I’ve got version 1 up and running see for the apk.
I will make a post about it.



Incredible! Thank you for all your work. This is wonderful.

It would be awesome if you could document this. @jcasman and I can help with editing.


Builds cleanly with zero errors!


Runs great.


Works great with exrdisplay on Linux. I can adjust the exposure, fogging.

1 Like

3 posts were merged into an existing topic: HDR plugin to automatically create EXR file. For VFX use

Very interesting your publication, although I don´t see your repository anywhere … I’m working on something similar and using OpenCV … Regards

1 Like

The repository is here:


Hey! I want to join this thread about OpenCV libraries and suggest you one good source and comment it. Can you check out for examle this article and after reply me in comment do you find it useful or not. Thanks!

Can you tell me the versions you are using of Android Studio, Gradle and OpenCV? … Have a nice day

Hi @guillengap,

  • Android Studio 3.3.2
  • Gradle 4.10.1
  • OpenCV 3.4.5
  • specify sourceCompatibility and targetCompatibility as 1.8 due to use of lambda

More info here:

1 Like

If you don’t have a camera, you should use this repo:

The big gotchas are:

  • Use OpenCV 3.4.5 (NOT 4.x which is the newest version)
  • Use Java 8 as example uses lambda expression

If you can’t use Java 8 due to policy restrictions at your organization, you can change the lambda expressions to Runnables. I think the Android Studio IDE may even ask you if you want the IDE to automatically change it for you.

Hi all,

I am getting following error,

error: undefined reference to ‘cv::HOGDescriptor::detectMultiScale(cv::_InputArray const&, std::ndk1::vector<cv::Rect, std::ndk1::allocator<cv::Rect > >&, double, cv::Size, cv::Size, double, double, bool) const’
clang++.exe: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [no-camera-opencv/app/build/intermediates/ndkBuild/debug/obj/local/x86/] Error 1

Can you someone help me on this?


1 Like

Are you running OpenCV 3.4.5?

Is your emulator x86?

Please provide your environment configuration.


Yes, I am using emulator on x86 machine. I have used OpenCV that is part of github repo.


Please confirm:

  • changed the include PATH in to the source of your specific location of OpenCV
  • enabled Android NDK in Android Studio
  • tried a make clean

Yes to all 3 points mentioned above.





I had similar environment, I revisited to ensure that my environment matches with above images and still no luck. Below is the code snippet I added to SDK,

HOGDescriptor hog;

vector<Rect> found, found_filtered;
hog.detectMultiScale(m_src, found, 0, Size(8,8), Size(32,32), 1.05, 2);


I can’t get it working. If you get a solution, please post the fix.

This did not work for me:

externalNativeBuild {
  cmake {
    arguments "-DANDROID_STL=gnustl_shared"

I also can’t get the build working with OpenCV 4.x

I think this is a common problem.

This is a better example of using OpenCV on the THETA

This looks like a nice article for OpenCV 4. I have not gone through it yet.

Update: 4/10/2019
Compiled OpenCV 4.1 last night on Windows as static libraries. Ran into problems using it with the plugin. Compiled OpenCV 4.1 on Linux with the following:

/OpenCV 4.1.0/opencv-opencv-0399435/platforms/android$ ./ --ndk_path ../../../../android-ndk-r19c-linux-x86_64/android-ndk-r19c/ --sdk_path ~/Android/Sdk/  ../../release/

Will report back on progress.