Update: Gradient Problems with 3D: It's Not Just Us!

"If the movie is being triple flashed as Disney often requires [see our article 'Where we're at with 3D' for more details], a second problem, colour banding or posterizaton, can occur. This will be evident in large mid-tone areas that slowly transition from one shade of gray or colour to another. Instead of being continuous, the transition will be in steps or bands."
 

Here's the graphic we used to illustrate the problem in our story on Monday:
 

"This occurs because, while the lenses of the glasses go to the opaque state very rapidly, the transition to the transparent state occurs slowly enough that it takes a significant portion of the frame interval. Normally this would just result in a small decrease in brightness, but, because of the way a DLP projector modulates light, there can also be a reduction of colour depth."

To understand this explanation, you need to understand how DLP projectors work.  To change the intensity of a particular colour across the screen and produce, for example, a purple gradient, the micro mirrors have to combine a mixture of red and blue.  Moving along the gradient, the intensities of each component vary.  Unfortunately, because 3D glasses alternate eyes so fast, they split up the gradient into smaller blocks.  Here's how it can happen and produce the rainbow effect with some projectors:
 

The photo taken at 1/200 s show that a very fast shot and split up the colours in a single frame.

Rentme3D suggests two separate solutions: adjusting the time in between each frame as well as the dark time, but recognizes that this approach has its limits.  If you go too far in one direction or the other, the picture can end up unstable or suffer from ghosting.