SSIM result is different from skimage.measure.compare_ssim

[Pixie8888]

Hi,
Thanks for this tool. I use both pytorch_mssim.ssim and skimage.measure.compare_ssim to compute ssim, but the results are different. For example, ssim evaluation on an image sequence:
pytorch_msssim.ssim: [0.9655, 0.9500, 0.9324, 0.9229, 0.9191, 0.9154]
skimage.measure.compare_ssim: [0.97794482, 0.96226299, 0.948432, 0.9386946, 0.93113704, 0.92531453]

Why will this happen?

[yifeipet]

I think the Pytorch MS SSIM is based on a differentiable MS SSIM algorithm so it's an approximation of the real MS SSIM.