convert Mat to Bitmap Opencv for Android

1) OpenCV Mat constructor expects <rows, cols> pair instead of <width, height> as its arguments. So you have to change your second line to

Mat tmp = new Mat (height, width, CvType.CV_8U, new Scalar(4));

2) Imgproc.cvtColor can change the dimensions of the tmp object. So it is safe to create a bitmap after the color conversion:

Bitmap bmp = null;
Mat tmp = new Mat (height, width, CvType.CV_8U, new Scalar(4));
try {
    //Imgproc.cvtColor(seedsImage, tmp, Imgproc.COLOR_RGB2BGRA);
    Imgproc.cvtColor(seedsImage, tmp, Imgproc.COLOR_GRAY2RGBA, 4);
    bmp = Bitmap.createBitmap(tmp.cols(), tmp.rows(), Bitmap.Config.ARGB_8888);
    Utils.matToBitmap(tmp, bmp);
}
catch (CvException e){Log.d("Exception",e.getMessage());}