Rotational direction of a blurry wheel

[CVhobbyist]

Let's say that a photo of a wheel is blurry because it rotates fast relative to the exposure time. Can one still tell in what direction the wheel is turning? Is there a way to determine that through photo analysis?

 

[KmH]

That would depend in some part on how blurred the wheel is.

Plus, there are usually other visual cues beyond the wheel itself in an image that indicate what direction a wheel is moving.

 

[Judobreaker]

If the only information you have on that photo is the blurry wheel rolling on a flat surface (let's say you had just a wheel and rolled it into the frame by hand) then no, you can not determine the direction of the wheel.

Take this picture for example: http://www.rakeshkapoor.us/ClassNotes/HTMLFiles/Rolling_20.gifThis photo could be made by rolling the wheel in both directions through the frame, it wouldn't make a difference whatsoever.

A better example would involve a car.
Take a look at this image: http://www.bmw.com/com/en/newvehicles/3series/sedan/2008/allfacts/effdyn/_shared/img/wheels.jpg
Which direction is it going? I bet you're gonna say forwards.
Sure, it is most likely going forwards but what if the car was put in reverse and the photo was taken...? How are you sure this isn't the case?

And what about this one: http://fc04.deviantart.net/fs36/i/2008/330/2/5/cupra_R_wheel_rolling_by_koosh_m.jpg
Can you tell me with 100% certainty which way the wheel is spinning?

 

[DaPOPO]

The third one the car is in for its emissions check and the tires are spinning with the car in drive. The car isn't moving at all....

 

[Judobreaker]

My point exactly. The surroundings in that photo aren't even hinting a direction. Sure you could guess the wheel is probably turning in the forward direction because that's what you usually do in these tests, but you can't know for sure.

 

[CVhobbyist]

With rolling shutters, which normal camera phones have, one can see that one half of the wheel is more blurry than the other half. The shutter follows the downwards movement so it gets sharper, but meets the upward movement so that part gets more blurry.

Here's a funny example:
Key differences between rolling shutter and frame (global) shutter.

View attachment 64714

 

[KmH]

Here is an example (#1) that shows direction - http://www.thephotoforum.com/forum/general-gallery/349817-ceiling-fan-2-shots.html