Monday, March 28, 2011

3D Terminology - Parallax Budget

I've seen a lot of different terms in the 3D community. I would like to address some of these terms and clarify what they really mean. It's not OK to use the wrong term to express an idea unrelated to that term. For example... The term "Parallax Budget" is often used to describe the "Apparent Distance" of an object. Parallax Budget alone does not have any of the values you need to calculate Apparent Distance so the two terms should not be used interchangeably. Also Parallax Budget is not the same as Depth Budget!

Parallax Budget is the range of parallax between the object with the most negative parallax and the object with the most positive parallax. It is often expressed as a % of screen width because that value scales relatively between screen sizes.

For example:
A range from (-5%) to (+5%) is a parallax budget of 10%
A range from (0%) to (+8%) is a parallax budget of 8%
A range from (-2%) to (0%) is a parallax budget of 2%

With this value alone you can know the exact location of one point. That point is the object that falls on the convergence point (if there is one). You can measure the tape distance from your eyes to the screen plane. Not very useful.

It is critical to know the maximum positive parallax number. When applied to your target screen size you can calculate the amount of divergence your audience eyes will have to do to see your images. It's extremely important that you try to avoid this scenario at all costs. Excessive divergence is the source of physical discomfort.

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