Motion blur ValueError when blur_limit is even

🐛 Bug

I’m not sure that this line https://github.com/albumentations-team/albumentations/blob/master/albumentations/augmentations/blur/transforms.py#L77 works as expected. It doesn’t take into account allow_shifted parameter at all, since there is or operator.

To Reproduce

Steps to reproduce the behavior:

1. A.Compose([A.MotionBlur(blur_limit=20)])

ValueError: Blur limit must be odd when centered=True. Got: (3, 20)

Expected behavior

I think that check for motion_limit should take the expression like this

if not allow_shifted and (self.blur_limit[0] % 2 != 1 or self.blur_limit[1] % 2 != 1):

Environment

• Albumentations version (e.g., 0.1.8): 1.3.0
• Python version (e.g., 3.7): 3.10.8
• OS (e.g., Linux): MacOs
• How you installed albumentations (conda, pip, source): pip
• Any other relevant information:

[Andredance]

@Dipet Error says that blur_limit should be odd when centered=True. I mean that this expression:

if not allow_shifted and self.blur_limit[0] % 2 != 1 or self.blur_limit[1] % 2 != 1:

doesn’t take into account allow_shifted parameter at all (If self.blur_limir[1] is even it will always raise an error if allow_shifted is True or False). If Motion blur works only with odd blur_limit we should specify it somewhere and make this expression without allow_shifted variable. What do you think?

[Dipet]

No, otherwise, It works with odd sizes only when allow_shifted=False. In that case we need odd value to make centered kernel. Yes. it will work correctly with even kenel sizes, but it maybe a little bit confusing whe you set limit to odd value, but it newer will be reached. At least we need warning that kernel is even and real limit is lower to by 1.