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VR-compliant post-processing effects in Unity

Unity Pro offers post-processing effects in the “Image Effects” package. Some of them are, by nature, not compatible with VR systems.

The two issues we will discuss are :

  • Break the stereoscopy

Thanks to parallax, stereoscopic images give our brain some clues to perceive the depth. A mandatory step for our brain is to detect that these slightly different left and right representations correspond to a single same object. This way, adding visual artifacts in only one image or deforming the parallax with 2D image deformations can generate too much incoherences for our brain and the result cannot be interpreted.

  • Create discontinuities at screens junctions

In a multi-screens system such a CAVE, a post-process effect must have continuous effects at physical screens edges. Generally, post-processing effects only use one image at a time. This way, an element that is out of the frame but close to a screens junction will influence only the image of it’s viewport and not the physically-close pixels of the next screen. The influence will immediately stop after the junction. This discontinuity is not natural and breaks the stereoscopy because both eyes don’t see the discontinuity at the same 3D space position.

pp1.png

This capture of the Fisheye effect shows an example of screen junctions issue. The effect generates discontinuities and the stereoscopy is especially broken at the character position. It is not visible here, but the fish eye also locally creates vertical offsets between the left and right images. This breaks the possibility of depth interpretation.

Here are the results of our tests:

pp2.png

 

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