Vizard 7 » Reference » Stereo & Displays » Stereo Modes » Frame sequential
7.6
Use this mode for devices that accept a single input for both the left and right eye channels.
Typical devices of this category are:
Frame sequential stereo requires third party hardware or software. These third party products will automatically intervene in Vizard's rendering cycle and create appropriate left and right eye images that are synchronized with the shutter device used for viewing.
At the professional end of the spectrum are graphics cards that support quad buffering. As an example, the entire line of nVidia "Quadro" series graphics cards support hardware quad buffering. Most of these cards have a port on the back of the card for synchronizing with shutter glasses.
Activate your graphics card's stereo mode, then start your script with the following:
WorldViz recommends nVidia Quadro cards for quad buffered stereo. Unlike the case for frame parallel stereo, you do not need to pass the viz.STEREO command when initializing your graphic environment. The hardware will automatically generate the stereoscopic views in a frame sequential manner. When this mode is properly engaged, you will see what will look like "ghosting" of your scene. More concretely, you will see two copies of your scene simultaneously superimposed over one another but shifted slightly horizontally relative to each other. The proper display hardware will trigger off of the embedded synchronization signal and properly separate these two images.
This mode works by using a single graphics channel of a computer and sending the different left and right eye images sequence on after another in time. In other words, the computer may first draw the left eye image, and then on the next frame draw the right eye image. A display device design to handle frame sequential images will segment this stream of alternating images and re-route the left-eye images to the user's left and the likewise for the right eye images. The advantage of this technique is that is requires simpler hardware all around and therefore the costs of such a system are usually considerably cheaper. The disadvantage of such a system is you essentially halve the amount of visual information presented to the user. Consider the case when your computer renders a virtual environment at 60 Hz. If half the images go to the left eye and the other half to the right eye, then each eye individual is only getting visual updates at 30 Hz. This compares to the frame parallel method that would send images to both eyes at a full 60 Hz rate. The consequences of frame sequential presentation can range from subtle to substantial. Halving 60 Hz to 30 Hz can result in quite noticeable flicker artifact that may bother some users. Stimulus involving fast motions will suffer considerably when the effective frame rate is only 30 Hz. However, many frame sequential devices work at higher input rates so if your computer can render at 120 Hz, you would then be back to 60 Hz in each eye.
The key to frame sequential presentation is properly synchronizing the left and right eye generation with the left and right eye display at the viewing end. If the synchronization is off, then the left eye is viewing the right image and vice versa. This is reversed stereo and will essentially void the stereo information you are attempting to present to the user. To ensure that the left and right eye images are delivered correctly, two main methods are used by different manufacturers. DDC coding embeds a synchronization signal in analog VGA signals outputted by the graphics card to the monitor. This signal is invisible but can be detected by display hardware in order to disambiguate which eye a particular frame is destined. The other main approach is to draw a thin blue line at the bottom of the screen whose length encode which is the target eye. Again, the display hardware detects this signal to maintain synchrony.
You should check with the technical documentation for your particular display device to identify which method it uses. To support both DDC and blue-line coding, Vizard works in conjunction with nVidia's Stereo drivers. For special information on setting up such stereoscopic equipment, you should go to nVidia's driver download page. You may also contact support@worldviz.com for some advice.