带有opencv的Android-图像到灰度

Question

I'm looking for simple example of app in Android which convert color image to grayscale using opencv. I'm trying with thic code, but app crash after this line Mat tmp = new Mat(bmp.getWidth(), bmp.getHeight(), CvType.CV_8U); .

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

    ImageView img=(ImageView)findViewById(R.id.imageView1);

    Bitmap bmp = BitmapFactory.decodeResource(getResources(),R.drawable.ic_launcher);

    Mat tmp = new Mat(bmp.getWidth(), bmp.getHeight(), CvType.CV_8U);

    Utils.bitmapToMat(bmp, tmp);

    Imgproc.cvtColor(tmp, tmp, Imgproc.COLOR_RGB2GRAY);
    Imgproc.cvtColor(tmp, tmp, Imgproc.COLOR_RGB2GRAY,4);

    Utils.matToBitmap(tmp, bmp);
    img.setImageBitmap(bmp);
}

Answer 1

Real quick way to do it. Without opencv.

 private Button button;
 private ImageView image;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    button = (Button)findViewById(R.id.button1);
    image = (ImageView)findViewById(R.id.imageView1);


    button.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {

            ColorMatrix matrix = new ColorMatrix();
            matrix.setSaturation(0);

            ColorMatrixColorFilter filter = new ColorMatrixColorFilter(matrix);
            image.setColorFilter(filter);


        }
    });

I just tried it, works for me.

edit: Check out the link here for official doc. http://developer.android.com/reference/android/graphics/ColorMatrix.html#setSaturation(float)

Answer 2

Your layout has not been laid out yet, while you are in onCreate() , that is why bmp.getWidth() and bmp.getHeight() return 0.
One way to do it is to override onWindowFocusChanged()

private ImageView img;
private boolean isFullyInitialized = false;

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

    img=(ImageView)findViewById(R.id.imageView1);
}


@Override
public void onWindowFocusChanged(boolean hasFocus)
{
    super.onWindowFocusChanged(hasFocus);
    if (hasFocus && !isFullyInitialized)
    {
        isFullyInitialized = true;
        openCvCode();
    }
}

private void openCvCode()
{
    Bitmap bmp = BitmapFactory.decodeResource(getResources(),R.drawable.ic_launcher);

    Mat tmp = new Mat(bmp.getWidth(), bmp.getHeight(), CvType.CV_8U);

    Utils.bitmapToMat(bmp, tmp);

    Imgproc.cvtColor(tmp, tmp, Imgproc.COLOR_RGB2GRAY);
    Imgproc.cvtColor(tmp, tmp, Imgproc.COLOR_RGB2GRAY,4);

    Utils.matToBitmap(tmp, bmp);
    img.setImageBitmap(bmp);
}

Answer 3

Problem solved:

public class MainActivity extends Activity {

ImageView img;
Bitmap bitmap;

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

    img=(ImageView)findViewById(R.id.imageView1);

    bitmap = BitmapFactory.decodeResource(this.getResources(), R.drawable.lena);

    if (!OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_2, this, mOpenCVCallBack))
    {
        Log.e("TEST", "Cannot connect to OpenCV Manager");
    }


}

private BaseLoaderCallback  mOpenCVCallBack = new BaseLoaderCallback(this) {
    @Override
    public void onManagerConnected(int status) {
        switch (status) {
                case LoaderCallbackInterface.SUCCESS:
                {

                    Mat tmp = new Mat(bitmap.getWidth(), bitmap.getHeight(),CvType.CV_8UC1);
                     // Convert
                    Utils.bitmapToMat(bitmap, tmp);

                    Mat gray = new Mat(bitmap.getWidth(), bitmap.getHeight(),CvType.CV_8UC1);
                     // Conver the color
                    Imgproc.cvtColor(tmp, gray, Imgproc.COLOR_RGB2GRAY);
                     // Convert back to bitmap
                    Mat destination = new Mat(gray.rows(),gray.cols(),gray.type());

                    Imgproc.adaptiveThreshold(gray, destination, 255, Imgproc.ADAPTIVE_THRESH_MEAN_C, Imgproc.THRESH_BINARY_INV, 15, 4);

                    Utils.matToBitmap(destination, bitmap);
                    img.setImageBitmap(bitmap);

                } break;
                default:
                {
                    super.onManagerConnected(status);
                } break;
            }
    }
    };

}