android-opencv converting mat to grayscale with using matToBitmap/bitmapToMat

Question

I am using newer opencv library of willowgarage in eclipse. And I want to convert a mat variable into grayscale, I've tried everything I found on the net but they didnt work for me.

Here is my code

package com.deneme.deneme;

import android.app.Activity;
import android.os.Bundle;
import android.widget.ImageView;
import org.opencv.android.Utils;
import org.opencv.core.Mat;
import org.opencv.imgproc.Imgproc;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
public class main extends Activity {
/** Called when the activity is first created. */

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

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

    Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.p26);

    Mat imgToProcess=Utils.bitmapToMat(bmp);

    //******
    //right here I need to convert this imgToProcess to grayscale for future opencv processes
    //******

    Bitmap bmpOut = Bitmap.createBitmap(imgToProcess.cols(), imgToProcess.rows(), Bitmap.Config.ARGB_8888); 

    Utils.matToBitmap(imgToProcess, bmpOut);
    img.setImageBitmap(bmpOut);
}

}

Answer 1

Add the following code in your code block:

Imgproc.cvtColor(imgToProcess, imgToProcess, Imgproc.COLOR_BGR2GRAY);
Imgproc.cvtColor(imgToProcess, imgToProcess, Imgproc.COLOR_GRAY2RGBA, 4);

Or you can access pixels by yourself:

for(int i=0;i<imgToProcess.height();i++){
    for(int j=0;j<imgToProcess.width();j++){
        double y = 0.3 * imgToProcess.get(i, j)[0] + 0.59 * imgToProcess.get(i, j)[1] + 0.11 * imgToProcess.get(i, j)[2];
        imgToProcess.put(i, j, new double[]{y, y, y, 255});
    }
}