InitUndistortRectifyMap and Remap

I am currently writing an openCV program for a pair of stereo cameras. Camera calibration as well as Stereo Calibration are done.

The next step is to find a feature's position in space from the 2 images I get. That's why I have to Stereo Rectify the images and make my calculations afterwards.

The problem I am facing with initUndistortRectifyMap is the following:

-If I pass R1 or R2 calculated by stereoRectify() to initUndistortRectifyMap() I get black images after remapping.

-If I pass r (an empty matrix) to initUndistortRectifyMap() I get unrectified images after remapping. The images I get are a little distorted though.

I need to pass R1, and R2, to initUndistortRectifyMap() for rectifying the 2 cameras, otherwise when passing an empty matrix the stereo heads won't be rotated into the same plane.

Following is my code:

stereoRectify(intrinsic[0], distCoeffs[0], intrinsic[1], distCoeffs[1], imageSize, 
    R, T_Stereo, R1, R2, newP1, newP2, Q, CV_CALIB_ZERO_DISPARITY, -1, imageSize);

if (x_Cam.GetSerial()=="4002678487")
{
    initUndistortRectifyMap(intrinsic[0], distCoeffs[0], R1, newP1, imageSize,        
        CV_16SC2 , mapx1,  mapy1);
    remap(x_Image, imageRectified[0],mapx1, mapy1, INTER_LINEAR);

    return imageRectified[0];
}   

if (x_Cam.GetSerial()=="4002702131")
{
    //flip(in, in, -1);
    initUndistortRectifyMap(intrinsic[1], distCoeffs[1], R2, newP2, imageSize, 
        CV_16SC2 , mapx2,  mapy2);
    remap(x_Image, imageRectified[1],mapx2, mapy2, INTER_LINEAR, BORDER_CONSTANT, 0);

    return imageRectified[1];
}

I checked all the matrix values going in to stereoRectify() and they are correct. The rotation matrices R1, and R2 seem to be correct as well. I am just getting black images as output.

I tried passing rubbish values into InitUndistortRectifyMap() for