something error in prepare.py

[AltoriaDD]

Hello,Thank you for your work
I find some Picture address error if you run as preapare.py set, in the line of 24，25, 26 ,78
cv2.imwrite(str(test_real_dir)+'{:05}.png'.format(img_idx),img)
The picture cannot be put into the address correctly, resulting in the subsequent py files not running normally.
So I made some changes：
cv2.imwrite(os.path.join(test_real_dir,'{:05}.png'.format(img_idx)),img)
Make the same change for similar parts
Hope it can be helpful for novices.

[wangxihao]

cv2.imwrite(os.path.join(test_real_dir,'{:05}.png'.format(img_idx)),img)

So kind, 3Q!