python計算PSNR

 將兩張圖都轉成float64進行計算，且歸一化到0~1，防止精度丟失

import numpy as np

def getpsnr(img1,bitdepth1,img2,bitdepth2):
    img1 = np.float64(img1) / (2**bitdepth1-1)
    img2 = np.float64(img2) / (2**bitdepth2-1)
    mse = np.mean(np.square(img1-img2))
    psnr = - 10 * np.log10(mse)
    return psnr