OpenCV将CV_8U转换为CV_64F。

I am trying to convert a grayscale image to the type CV64F. From the OpenCv documentation I have understood that a grayscale image is of the type CV_8U. I have also found that imshow plots different types differently, hence I need to divide by 255 before converting. But after converting the image I still get many saturated pixels.I am trying to convert a grayscale image to the