ANDROID - color detection using openCV - how to?

my goal is to display a threshed image using the HSV color space in a way that only yellow objects will be shown. i use this code (based on a code given by the openCV 2.3.1 android samples):

protected Bitmap processFrame(VideoCapture capture) {
    //capture.retrieve(mGray, Highgui.CV_CAP_ANDROID_GREY_FRAME);
    //Imgproc.cvtColor(mGray, mRgba, Imgproc.COLOR_GRAY2RGBA, 4);

    capture.retrieve(mHSV, Highgui.CV_CAP_ANDROID_COLOR_FRAME_RGBA);
    Imgproc.cvtColor(mHSV, mRgba, Imgproc.COLOR_RGB2HSV, 4);
    //Core.inRange(mRgba, new Scalar(20, 100, 100), new Scalar(30, 255, 255), mRgba);

    Bitmap bmp = Bitmap.createBitmap(mRgba.cols(), mRgba.rows(), Bitmap.Config.ARGB_8888);

    if (Utils.matToBitmap(mRgba, bmp))
        return bmp;

    bmp.recycle();
    return null;
}

the base (Abstract)class contains the "run" method:

protected abstract Bitmap processFrame(VideoCapture capture);

public void run() {
...
bmp = processFrame(mCamera);
...
canvas.drawBitmap(bmp, (canvas.getWidth() - bmp.getWidth()) / 2, (canvas.getHeight() - bmp.getHeight()) / 2, null);
...
}

i get this distorted preview which i think i can understand (HSV format) but why is it repeating itself (i`v draw a green line to emphasize it) 4 time? and what is the black horizontal line? what am i doing wrong?

one last thing, what is the logic behind:

Imgproc.cvtColor(mHSV, mRgba, Imgproc.COLOR_RGB2HSV, 4);

why is it COLOR_RGB2HSV? shouldnt it be COLOR_HSV2RGB?

Let's say i'v passed this problem, how can i make a gray level image with the yellow objects in their native color? i thought using the Core.inRange() method but when i do this i get black screen.

yes, i guess i look like a total jerk but i need to start from somewhere, don't i?

10x!

Update 1: i tried