Python3.5-How to delete (release GPU memory) a variable from inside a function

I defined a function in Python 3.5 called 'evaluate' and the code is shown below ('REC_Y', 'REC_U', 'REC_V' represent the 3 channels of a YCbCr image respectively):

import numpy as np


def evaluate(REC_Y, REC_U, REC_V):
    height = 832
    width = 480

    bufY = np.reshape(np.asarray(REC_Y), (height, width))

    bufU = np.reshape(np.asarray(REC_U), (int(height / 2), int(width / 2)))
        
    bufV = np.reshape(np.asarray(REC_V), (int(height / 2), int(width / 2)))
    
    return (np.stack((bufY, bufU, bufV), axis=2))   

In order to release some GPU memory (since I already had a GPU MemoryError), I'd like to remove 'REC_Y','REC_U','REC_V' from memory after the last line of the code (after 'bufV = np.reshape(np.asarray(REC_V), (int(height / 2), int(width / 2)))'). I have tried 'del REC_Y', but it shown 'REC_Y' referenced before assignment. I have tried del global()["REC_Y"] but it shown that "REC_Y" is not defined as a global variable.

Could you please help me with this issue? How to delete 3 parameters of 'evaluate' function to release GPU memory?

Many thanks!

Numpy does not work on GPU.

Only if you had CUPY or CUDA operations could you try to free some memory on the GPU -> numpy works on CPU.