Support of 3D Video Formats
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 may become an issue with accurately presenting fast-moving images.
Side-by-side and top/bottom multiplexing provide full-rate updates to each eye, but reduce the resolution presented to 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.
Not all HMDs provide depth perception. Some lower-end modules are essentially bi-ocular devices where both eyes are presented with the same image.
3D video players sometimes allow maximum compatibility with HMDs by providing the user with a choice of the 3D format to be used.
Read more about this topic: Head-mounted Display
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