Ask Your Question

Revision history [back]

Sending Opencv images from Android to PC over TCP

I'm working on a Android app that grabs a image and sends it to a PC client for display, both the Android app and PC application use Opencv. The image that i want to send over is a color image (grabbed in the rbga format).

First i grab a image in the java app using:

InputImage = inputFrame.rgba();

Next i am using the Mat image variabele and convert the input image to a byte array using the following native (using JNI) function:

    JNIEXPORT jbyteArray JNICALL Java_com_example_communicationmoduleTCPIP_communicationmoduleTCPIP_ConvertImageToByteArray(
        JNIEnv* Env, jobject,
        jlong addrInputImage){

    Mat& OutputImg = *(Mat*) addrInputImage;
    jbyteArray Array;

    //__android_log_write(ANDROID_LOG_ERROR, "Tag", "==== 1 ");

    // Init  java byte array
    Array = Env->NewByteArray(1536000);

    //__android_log_write(ANDROID_LOG_ERROR, "Tag", "==== 2 ");

    // Set byte array region with the size of the SendData CommStruct.
    // Now we can send the data back.
    Env->SetByteArrayRegion(Array, 0, 1536000, (jbyte*);

    //__android_log_write(ANDROID_LOG_ERROR, "Tag", "==== 3 ");

        return Array;

Next is end the byte array (containing the image data) over TCP with the following function:

    // Send buffer, the method can be used by both client and server objects.
    public void SendByteBuffer(byte[] ByteBuffer){

    try {                         
        // Get socket output stream
        OutputStream OutputBuffer = ClientSocket.getOutputStream();

        //Write byte data to outputstream

    catch (IOException e) {
        Log.e("TCPIPCommunicator: ", "Client: Failed to send", e);

On the PC side (in c++) i recieve the buffer with a boost lib recieve function:

int CommunicationModuleTCPIPServer::RecieveBuffer(char Buffer[], int Size){

boost::asio::read(ServerSocket, boost::asio::buffer(TempBuffer, 1536000));
//boost::asio::read(ServerSocket, boost::asio::buffer((char*)InputImage, Size));
//cout <<"Temp buffer: " << TempBuffer << endl;

 int ptr=0;
 for (int i = 0;  i < InputImage.rows; i++) {
  for (int j = 0; j < InputImage.cols; j++) {<cv::Vec4b>(i,j) = cv::Vec4b(TempBuffer[ptr+ 0],TempBuffer[ptr+1],TempBuffer[ptr+2],TempBuffer[ptr+3]);



And then i display the variable with the imshow function of opencv. The problem is that i don't get a image in the window on the pc side. i'm thinking the conversion is going wrong somewhere but i dont' see where. Does anybody have a idea? All suggestions and feedback are welcome!