I don’t know why, but it always bothers me when I see a car commercial and the tires appear to be spinning backwards. Actually, at slow speeds, they look fine, but when the car gets going fast they spaz out and start going backwards (to my eye). This is no doubt a strobe effect related to the shutter speed on the cameras and/or the refresh rate of the television. Since those are both pretty much set in their ways, I propose that the only way to fix this illusion is to alter the car itself.

I think the easiest way to do this is to equip the car with a set of high tech spinner rims. As I understand it, regular spinner rims (see link) have two parts to them. One part actually holds the tire and attaches to the axle and the other part is a fancy faceplate that fits in a groove and is free to rotate. The effect of this is that when your car gets going, the faceplates begin to spin and then when you stop, they continue to spin for a while… pretty nifty.

The high tech spinner rims however, would not be free to rotate as the pleased. At slow speeds, they would be locked in position so that they rotate with the wheel. Then when they reach the higher speeds that begin to cause the television illusion, they would begin to rotate backwards. They could be geared up to rotate in the reverse direction with a rate proportional to the rotation of the wheel itself. That way, when you see these rims on a car commercial, they will actually appear to be spinning forward, at the correct speed.

I suppose there may still be some funny imagery in the transition from low to high speeds, but at least the cars would look normal in either extreme.
-- luecke, Jun 15 2004

Spinner Rims http://www.truckxpr...ys/spinning_rim.htm
the normal version [luecke, Oct 04 2004, last modified Oct 05 2004]

The Wagon Wheel Illusion http://www.bu.edu/s...namorphic/wade.html
Speed 1 works best [ldischler, Oct 04 2004, last modified Oct 05 2004]

Hi-poly 2004 Celica dataset http://snipurl.com/755k
Bring money. [bristolz, Oct 04 2004, last modified Oct 05 2004]

100% CGI http://snipurl.com/755q
Pretty convincing, no? [bristolz, Oct 04 2004, last modified Oct 05 2004]

100% CGI http://snipurl.com/755m
An outdoor “shot.” [bristolz, Oct 04 2004, last modified Oct 05 2004]

finalrender motion blur http://snipurl.com/7569
Beautiful stuff. [bristolz, Oct 04 2004, last modified Oct 05 2004]

Assuming that it has to do with the wheel's rotational position at the time each frame is captured, would spinning it backward really always make it look like it was going forward?

I was expecting it to allow the spinners to rotate at only specific speeds (some harmonic of the frame rate) or to be controlled by the camera to allow setting of an absolute position for each frame.
-- half, Jun 15 2004


Use a variable timing strobe light. That way, you can make the tires look like they're going forward or reverse at a user selectable speed, or just standing still regardless of how fast the car is moving.
-- phoenix, Jun 15 2004


I have no doubt that the car commercials do the "backward tire thing" on purpose. It makes the car look like it's whizzing by silently and smoothly. Meanwhile the piece of crap is probably puttering along at 15 mph while billion-dollar cameras are panning around to speed up the scenery.

You know what, [luecke]? Just last night I thought of posting an idea here for "car with tires that move forward"! We'd be the only company whose cars have tires that travel forwards instead of in reverse, and we'd make a trillion bucks. + for you for thinking like me :)
-- phundug, Jun 15 2004


An artist I know used a high speed camera and afterwards elimated pictures so any backward spinning effect was suppressed.

<Opinion>Those Spinner Rims in the link are just nuts and it is hard for me to believe that anyone would install them.</O>
-- kbecker, Jun 15 2004


[half] - I think spinning it backwards would have to have the exact opposite effect of the regular tire. Sure a regular tire will not appear to be backwards at all speeds, but it seems like it does for most of the speeds they use in car commercials, so I figured the easiest way around this was to reverse the motion during the problematic times. No doubt the speed of the backwards rim would have to be controlled to produce this end effect, not simply to go at the same speed of the tires (in reverse).

[phundug] - I'm eagerly awaiting the arrival of my half-trillion dollar check. You put it in the mail, right?
-- luecke, Jun 15 2004


As the wheel accelerates, it will alternate between appearing to move forward and backward. Once the wheel stops accelerating, it will appear one way or the other. If the car company wanted it to appear to spin forward, they could just choose the appropriate speed. However, once the wheel gets past a certain speed, it can never appear to be spinning as fast as it is actually spinning. I would guess that this influences the car companies to set it up so the wheels appear to spin backwards. Otherwise it would just look like the wheels are spining too slow (not very dramatic). You could implement your idea, not by making the hubcaps spin backwards, but simply by making sure they never spin faster than the fastest apparent speed.

That speed depends not only on the frame rate, but also on the symmetry of the wheel. For example, a wagon wheel with 16 spokes has 16 different positions that look identical. A three spoke car wheel only has three, so it can spin much faster before it appears to reverse.

I suspect that it's actually very difficult (maybe impossible without specialized editing) to film a car with existing equipment such that it appears realistic. As a baseline, look out the window while driving on the highway. Notice that the wheels appear to be a blur. Often you can see right through them to the brakes rotors if there are big enough holes in the wheel. Sometimes it looks almost like the car is levitating, or like the wheels are made out of some solid semi-transparent material. Getting that effect with film is tricky. If you use normal high speed film, the wheels aren't blurred enough. If you use film slow enough to blur the wheels, the car itself will look a little blurred, or if the camera is tracking the car's movement, the car could be clear, but the background will be blurred. We see a real car as not being blurred because our eyes track the car. We see the wheels as blurred even though they aren't moving any faster than the car because our eyes can't track the circular motion. When we are focused on the car, the background is probably blurred, but we don't notice because we are focused on the car. When we focus on the background, it looks clear, but the car is probably blurred. However, on film the car and the background must be clear at the same time because you never know what part of the screen the viewer is focused on, so the film must be high enough speed not to blur the car and background, but slow enough to blur the wheels (which are moving no faster than the car).
-- scad mientist, Jun 15 2004


The problem seems unique to the author.
-- waugsqueke, Jun 15 2004


Hmmm...is that a disqualifier?
-- half, Jun 15 2004


Nope, merely an observation.
-- waugsqueke, Jun 15 2004


Those spinner rims are all the rage here in Motown. I must see 10 of 'em on my way to work.
-- RayfordSteele, Jun 16 2004


Not to knock the idea which I think is imaginative and funny but why fight the physical problem when you can fake it to perfection?

Place high contrast markers on the centers of the car wheels and a high contrast stripe about the perimeter of the wheels. Do your film production/shoot. In post, generate tracking data and camera match data for the wheels using the high contrast markers as track points. In 3D, using a CAD model of the wheel from the auto manufacturer's design center and using the tracking and cam match data, animate wheels with the appropriate corrected motion, motion blur and lighting--a false, but correct looking, caricature of the wheels, if you will. Finally, back in post, composite the animated wheels upon the film plate replacing the physical wheels with the synthetic wheels. Since the viewer will never see any shots with the real wheels, they'll have no AB comparison and it'll be hard for anyone to know they are composites.

Alternatively, generate the entire vehicle in 3D and match motion to empty road BG plates and composite. Many of the cars you see in commercials are 100% CGI these days, especially the ones in a studio setting that rotate as if they are on a turntable. Viewpoint Data Labs (now Digimation) has built a large business selling very high poly count 3D datasets of cars for the car commercial business. Other companies, like Splutterfish, have written high-end car paint, chrome and glass shaders along with gorgeous lighting systems for eye-poppingly photorealistic renderings of cars. (links)

For just the wheels, the best rotational motion blur I've seen is from Cebas, with their finalrender package.

Sorry for blathering on.
-- bristolz, Jun 17 2004



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