Android Jni 利用OpenCV 實現圖像尺寸縮放(三)

原創

2020-02-21 21:14

一，利用OpenCV的pyrDown（）實現圖像縮小，上java代碼

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

private Button btnProc;
private ImageView imageView;
private Bitmap bmp;

// Used to load the 'native-lib' library on application startup.
static {
    System.loadLibrary("native-lib");
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // Example of a call to a native method
    btnProc = (Button) findViewById(R.id.btn_gray_process);
    imageView = (ImageView) findViewById(R.id.image_view);

    bmp = BitmapFactory.decodeResource(getResources(), R.drawable.test3);
    imageView.setImageBitmap(bmp);
    btnProc.setOnClickListener(this);
}

/**
 * A native method that is implemented by the 'native-lib' native library,
 * which is packaged with this application.
 */
public static native int[] grayProc(int[] pixels, int w, int h);


@Override
public void onClick(View view) {

    int w = bmp.getWidth();
    int h = bmp.getHeight();
    int[] pixels = new int[w*h];
    bmp.getPixels(pixels, 0, w, 0, 0, w, h);

    long startTime = System.currentTimeMillis();
    int[] resultInt = grayProc(pixels, w, h);
    long endTime = System.currentTimeMillis();

    w = w/2;
    h = h/2;

    Log.e("JNITime",""+(endTime-startTime));
    Bitmap resultImg = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);

    //(@ColorInt int[] pixels, int offset, int stride,int x, int y, int width, int height)
    resultImg.setPixels(resultInt, 0, w, 0, 0, w, h);
    imageView.setImageBitmap(resultImg);

}

}

二，實現jni方法

extern “C”
JNIEXPORT jintArray JNICALL
Java_com_example_dgxq008_opencv_1readpixel_MainActivity_grayProc(JNIEnv *env, jclass type
, jintArray pixels_
, jint w
, jint h) {

jint* pixels = env->GetIntArrayElements(pixels_, NULL);
if (pixels==NULL){
    return 0;
}

//圖片一進來時是ARGB  通過mat轉換BGRA
Mat img(h,w,CV_8UC4,(uchar *)pixels);  //pixels 操作的是同一份數據

// Mat out;
// cvtColor(img,out,COLOR_BGRA2RGB);
//
// //對應數據指針
// uchar* ptr = img.data;
//
// int length = w*h;
// int i;
// for (i = 0; i < length ; ++i) {
// ptr[4*i+0] = 0;
// ptr[4*i+1] = 0;
// ptr[4*i+2] = ptr[4*i+2];
// }

Mat temp;

//進行向上取樣操作
//( InputArray src, OutputArray dst,const Size& dstsize = Size(), int borderType = BORDER_DEFAULT );

//縮小原圖的一倍
pyrDown( img, temp, Size( img.cols/2, img.rows/2 ) );

//對應數據指針
uchar* ptrTemp = temp.data;

int size = w*h/4;
jintArray result = env->NewIntArray(size);
env->SetIntArrayRegion(result,0,size,(jint*)ptrTemp);

env->ReleaseIntArrayElements(pixels_, pixels, 0);

return result;

}