Stereo

How stereo viewing works

The illusion of 3D depth is performed by showing slightly different images to left and right eyes.

The hardware makes available "left" and "right" buffers, and swaps between them alternately - usually at 120 frames per second (120Hz).

Stereo glasses, synchronised with the display, shutter each eye in turn so that it only sees "its" image 60 times per second.

The 60Hz per eye refresh rate is faster than the eye can perceive, therefore the brain is fooled into thinking that it is seeing a single image viewed from two slightly different eye positions, and assembles this into the illusion of depth.

In order for this illusion to work the angular separation of the left and right images must approximate the "squint" angle that would actually occur when a viewer at a typical distance of about 600mm from a display looks at an object "behind" the plane of the display, ie somewhere "inside" the display.

Since eyes are typically about 80mm apart this means that each eye needs to "squint" inwards by an angle of approximately 2 degrees in order to give the correct apparent location of the object, and the left/right image projections are adjusted to give this angle.

Adjusting stereo separation

In practice users will not always be the expected distance from the screen, screen sizes vary, and indeed perception of depth varies from individual to individual. In other words there is no "perfect" setting that will please everybody all the time. In addition people with somewhat wonky vision (like the author!) may find too much stereo separation to be hard to view and - at worst - headache inducing.

Therefore D3PLOT has two modes for controlling stereo depth.

In both cases you can both increase and decrease stereo separation by using More sep <<==>> and Less sep >>==<<, which will adjust either mode by 5% per click.

Reset all to default will restore the default setting.

Recommended practice

Achieving a satisfactory result is likely to be obtained by:

Setting up stereo viewing

You usually only need to do this once, but getting it all to work that first time can be a challenge. This is only a brief description, if you need more help please contact Oasys Ltd Support with details of your equipment.

Hardware Prerequisites:

• The monitor or display device must be able to refresh at 120Hz.
  
  This is twice the normal 60Hz refresh rate of a standard LCD display, and typical monitors will not support this. Monitors that do are often described as being "3D capable", but the key metric is that 120Hz refresh rate. Sometimes such monitors are sold as having a "1ms response time", and most will actually refresh at up to 144Hz.
  
  The reason for this is that stereo requires separate "left eye" and "right eye" images to be drawn in quick succession, requiring twice as many redraws as a normal mono image. If the result is not to flicker this must be done at twice the normal 60Hz rate.
  
  
  
• The cable between graphics card and monitor must support this refresh rate.
  
  Direct "Display Port" or HDMI cables will usually support this, but simple passive adapters between these formats generally will not.
  If using DVI-D the cable must be a "dual link" cable with all pins present. It will be marked as such on the plugs.
  Old-fashioned VGA cables almost certainly will not support it.
  
  
  
• You need some sort of 3D display hardware.
  
  This might be 3D glasses with an Infra Red (IR) or radio frequency emitter to sychronise with the graphics card, or some other hardware.
  
  In addition your graphics card must support stero rendering. Most modern cards will, but for some "engineering" cards such as NVidia's Quadro range it may be necessary to buy an additional adapter into which to plug the stereo hardware.

Software Configuration:

• The graphics driver software must support stereo viewing.
  
  This should not be a problem for any driver installed since about 2012, but it is worth checking that it does and whether any additional downloads are required.
  
  
  
• The stereo display must be the primary display on the computer.
  
  If you have multiple monitors and only one supports 120Hz refresh rates it must be the primary display.
  
  
  
• The stereo display must be configured to refresh at 120Hz or faster.
  
  Normally even a "3D capable" display will be configured by default to run at 60Hz, and you will need to configure it manually to run at the faster rate.
  On Windows 10 it is also necessary to designate the display as being in "3D display mode".
  
  
  
• It may be necessary to run a stereo setup "wizard" in the graphics driver configuration.
  
  This may perform first-time initialisations of hardware and software drivers.
  In the case of NVidia drivers it is also necessary to enable stereo in their "3D settings" list.

Avoiding, or at least mitigating,"slow flicker" effects caused by ambient lighting

You probably won't observe this, especially if the lighting in your environment is modern, high quality or natural. But if you experience an annoying "slow flicker" effect in your peripheral vision when using 3d glasses this section may help.

Stereo glasses alternate between left and right eyes at 120 frames per second, hence the requirement for a monitor running at a refresh rate of 120Hz, which means that each eye is "shuttered" at a rate of 60 frames per second (60Hz). Some forms of lighting, especially fluorescent tubes, can flicker a bit at the frequency of the electricity supply which tends to be 60Hz in the USA, but 50Hz in Europe and much of the rest of the world. Therefore when using stereo glasses it is possible for the "shutter" effect of the glasses to heterodyne with the "flicker" effect of the ambient lighting, giving a "slow flicker" effect in peripheral vision at the difference between these two frequencies.

In the USA where glasses and mains electricity supply are running at more or less the same frequency the effect is not likely to be noticeable, but when the difference is around 10Hz as in Europe and elsewhere the effect can be quite noticeable - and rather annoying. There are various things you can do to mitigate this:

• The cause is the ambient lighting in your environment, so if you can change this the problem will go away. The simplest solution is to turn it off, but replacing worn-out fluorescent tubes or moving to LED lighting may well solve the problem. Alternatively relocating the stereo hardware closer to a window, where natural light predominates (the sun doesn't flicker!) may help.
  
  
• If that is not possible then, depending on your hardware, you may not be forced to use exactly 120Hz as your screen refresh rate. Most 3d-capable monitors will support frequencies up to 144Hz, so if your graphics card will drive them at that frequency and - crucially - your 3d hardware will synchronise at different speeds, it is worth trying different values. Remember that the slow flicker is more or less at the difference between lighting and glasses frequencies, so changing that difference may move it to a regime to which the human eye is less sensitive.

Of the two solutions fixing the ambient lighting is much the best - possibly a "Health and Safety" issue?