Issue with Stereo Binary BM

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I have a stereo pair with a resolution of [640 x 480] grayscale. My program keeps crashing when computing the disparity.

auto sbm = cv::stereo::StereoBinaryBM::create(16, 9); //have tried 32, 64
cv::Mat disparity; 
sbm->compute(im_00, im_01, disparity);

When I initialized the disparity mat however, I get a weird output

auto sbm = cv::stereo::StereoBinaryBM::create(16, 9); //have tried 32, 64
cv::Mat disparity = cv::Mat::zeros(im_00.size(), CV_16SC1);
sbm->compute(im_00, im_01, disparity);