Android Jni 利用OpenCV 实现图像尺寸缩放(三)

一，利用OpenCV的pyrDown（） 实现图像缩小，上java代码

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，实现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;
}

//图片一进来时是ARGB  通过mat转换BGRA
Mat img(h,w,CV_8UC4,(uchar *)pixels);  //pixels 操作的是同一份数据

// Mat out;

// cvtColor(img,out,COLOR_BGRA2RGB);

//

// //对应数据指针

// 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;

//进行向上取样操作
//( InputArray src, OutputArray dst,const Size& dstsize = Size(), int borderType = BORDER_DEFAULT );

//缩小原图的一倍

pyrDown( img, temp, Size( img.cols/2, img.rows/2 ) );

//对应数据指针
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;

}