Cómo cambiar el tamaño de la imagen antes de agregarla al archivo xml

I have many bitmaps in my xml file and I'm getting an out of memory exception.

I have this code to resize the bitmaps to reduce the space.

public static Bitmap decodeSampledBitmapFromResource(Resources res,
            int resId, int reqWidth, int reqHeight) {

        // First decode with inJustDecodeBounds=true to check dimensions
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeResource(res, resId, options);

        // Calculate inSampleSize
        options.inSampleSize = calculateInSampleSize(options, reqWidth,
                reqHeight);

        // Decode bitmap with inSampleSize set
        options.inJustDecodeBounds = false;
        return BitmapFactory.decodeResource(res, resId, options);
    }

How can I use this code to resize the images in my drawable folder BEFORE they are added in the xml file so I dont get an out of memory exception?