Monday, March 7, 2011

Side by Side 3D and HMDs

A key advantage of HMDs over 3D televisions is the ability to get true depth perception in a surround video setting. However, depth perception inside an HMD requires different images for the left and right eyes. There are multiple ways to provide these separate images:

  • Use dual video inputs, thereby providing a completely separate video signal to each eye
  • Time-based multiplexing. Techniques such as frame sequential combine two separate video signals into one signal by alternating the left and right images in successive frames.
  • Side by side or top/bottom multiplexing. This method allocated half of the image to the left eye and the other half of the image to the right eye.
The advantage of dual video inputs is that it provides the maximum resolution for each image and the maximum frame rate for each eye. The disadvantage of dual video inputs is that it requires separate video outputs and cables from the device generating the content.
Time-based multiplexing preserves the full resolution per each image, but reduces the frame rate by half. For example, if the signal is presented at 60 Hz, each eye is receiving just 30 Hz updates. This becomes an issue with accurately presenting fast-moving images, or images that need to rapidly change as a result of tracking information or user movement.
Side-by-side and top/bottom multiplexing provide full-rate updates to each eye, but reduces the resolution presented to each eye because only half the available pixels in each frame are used for each eye. Many 3D broadcasts, such as ESPN, chose to provide side-by-side 3D which saves the need to allocate extra transmission bandwidth and is more suitable to fast-paced sports action relative to time-based multiplexing techniques. Of the multiplexing techniques, I think side by side 3D is best for HMDs.
Side by side 3D has some advantages over the full dual-port mode when using a wireless video link. Sending two completely separate images requires a dual-stream video link or two separate transmitters. With side-by-side, true interactive 3D can be economically achieved with a single wireless video link.
Not all HMDs provide depth perception. Some lower-end modules are essentially bi-ocular devices where both eyes are presented with the same image. Interestingly, most professional HMDs do not provide support for side-by-side format. Fortunately for users, both the xSight and zSight professional HMDs do provide such support. Such support also allows you to tap into the wealth of entertaining 3D videos on YouTube 3D, view video directly from a 3D camera and more.

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