Image converted to grayscale using opencv and JNI draws 4 small grayscle images

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When I convert RGB image to Grayscale image it returs 4 same images but size smaller than original image. I tried but didn't able to solve this..

I get help from this source...

How to do real time image processing in Android using OpenCV?

Below is my code for JNI function...

JNIEXPORT void JNICALL Java_com_example_hellojnic_HelloJNI_ImageProcessing2(JNIEnv*env,
            jobject thiz, jint width,   jint height, jbyteArray p_data, jintArray bgra)
{

     jbyte* _p_data= env->GetByteArrayElements(p_data, 0);
     jint* _bgra = env->GetIntArrayElements(bgra, 0);

     Mat mdata(height, width, CV_8UC4, (unsigned char *)_p_data);
     Mat mbgra(height, width, CV_8UC1, (unsigned char *)_bgra);

     cvtColor(mdata, mbgra, CV_BGRA2GRAY);

     env->ReleaseIntArrayElements(bgra, _bgra, 0);
     env->ReleaseByteArrayElements(p_data, _p_data, 0);

}