单击较亮像素时，OpenCv Mat :: at抛出异常

Question

我有以下代码

void Segmentation::CallBackFunc(int event, int x, int y, int flags, void* param)
{
    Vec3b bgrPixel;
    int i = 0;
    //Press 0, if face
    if (event == EVENT_LBUTTONDOWN)
    {
        Mat &img = *((Mat*)(param)); // 1st cast it back, then deref
        circle(img, Point(x, y), 3, Scalar(0, 255, 0), 2);
        try
        {
            bgrPixel = img.at<Vec3b>(x, y);
        }
        catch (Exception ex)
        {
            string message = ex.msg;
        }
        imshow("Display window", img);

一切正常，直到我点击相对较亮的像素（例如白色）。在这种情况下，我收到以下例外：

error: (-215) dims <= 2 && data && (unsigned)i0 < (unsigned)size.p[0]
    && (unsigned)(i1*DataType<_Tp>::channels) < (unsigned)(size.p[1]*channels())
    && ((((sizeof(size_t)<<28)|0x8442211) >> ((DataType<_Tp>::depth) & ((1 << 3) - 1))*4) & 15) == elemSize1()
    in function cv::Mat::at