pic should be Tensor or ndarray. Got <class 'numpy.ndarray'>

I followed the ReadMe.md step by step, but the image read by `cv2.imread` cannot work in `mask_generator.generate`
It raised a `TypeError: pic should be Tensor or ndarray. Got `, why `` is not `ndarray`?????

Reproduce the README.md workflow using cv2.imread and mask_generator.generate, then inspect the image type at the handoff where the TypeError occurs. Compare the reported type with the type accepted by generate; done means the cause is documented and the README workflow either succeeds or clearly states the required compatibility conditions.

Written by the indexing model from the issue text.