[Python] OpenCV imshow shows very grainy image. How to fix this?

I have a CT image that look like this when I plot it using dicom:

But when I try to use opencv, it appears like this:



Array is dtype=uint16. My code to visualize in OpenCV:

img = np.array(ct_img * 255, dtype = np.uint16)
cv2.imshow('Annotated',img)
cv2.waitKey(0)


Please help fix the image. Image quality gets worse when I convert to np.uint32 or np.unint8

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