Published on 04/28/2012

Real depth for real fun

  • Real depth for real fun

If you have a 3D TV or projector, you may be lamenting about the lack of 3D contents. Time to take things into your own hands! With Tao Presentations, you can create yourself 3D animations on your display, and discover the magic of 3D storytelling. Whether you want to give a new touch to your photo album or show off the growth curve of your startup, 3D can really add a unique touch to your presentations.

There are many ways to display depth on a screen. Tao Presentations supports the large majority of them. This article will discuss the different types of 3D display, their respective benefits, and how to best take advantage of them.

 

A few 3D display modes

The following video shows a few of the many 3D display modes available in Tao Presentations. In the video, the various modes are selected using the built-in command menu, which you can activate by pressing the Escape key on the keyboard. You can also select the display mode with the View menu entry. The presentation being shown can be dowloaded directly in Tao Presentations, and is discussed here.

3D Display Technologies

The first thing to consider is the display technology at your disposal. The main techniques to display in 3D are:

  • Anaglyph: the picture for each eye is colored with a different tint, most often red and cyan. This technique works on all display types. It requires very inexpensive glasses, that you can build yourself using transparent plastic film.
  • Passive glasses: the picture for each eye is polarized differently. The current standard is to use left and right circular polarization. The glasses contain polarizing filters. They are relatively inexpensive and lighteweight. They do not cause stroboscopic effect in the presence of high-frequency lights like fluorescent tubes. The technology works slightly differently for projectors and TVs:
    • Passive 3D projectors create two distinct pictures that are superimposed on the screen. It is possible to rig together two different projectors. The mai drawback is that the screen must preserve light polarity, which is not the case for most surfaces. The recommended screens are metallic, expensive, and fragile. They are more suitable for a fixed installation like a movie theater than for occasional events.
    • Passive 3D TVs have a mask that separate even and odd rows on the screen. Each of the eyes therefore receives half the vertical resolution (i.e. 540 lines for a FullHD TV).
  • Active glasses: The pictures for each eye are presented one after another on the screen, at a high refresh rate (for example 120Hz meaning 60Hz per eye). Glasses containing some electronics to synchronize with what is being shown using a specific signal, most often infrared. There are many types of active glasses. Glasses designed for the movie theater will not work at home. Fortunately, Texas Instruments practically defined a standard called DLP-Link for digital projector, which means that DLP-Link glasses are compatible with one another.
  • Autostéréoscopy: A lenticular grid or a parallax grid will separate pixels so that one person standing at the right distance of the screen will see depth without glasses. The simplest versions of these screens are for a single viewer. They can be found for example in the Nintendo 3DS console. Screens of larger sizes, up to 55 inch at least, are now available, which allow several people to see the 3D effect from different positions. These screens are sometimes called "multi-scopic". On this market, two very different design philosophies exist:
    • Companies like Alioscopy use a specific pattern of pixels on screen to create several viewpoints (8 view points for Alioscopy, i.e. 7 stereoscopic pairs). This kind of screen offers not just real parallax, but also true transparency effects. In the case of Tao Presentations, this class of screens also supports rendering videos from standard stereoscopic movies (e.g. side-by-side) with real-time conversion.
    • The Dimenco technology uses a depth map, where one half of the display specifies the color, and the other half specifies the depth. Electronics integrated in the screen will then convert this format into the proper pixel pattern. Creating this kind of picture is easier, and the format is compatible with different layouts of the pixels and lenticular grids. On the other hand, since there is only one depth information per pixel, it is very hard to create realistic transparency effects on these screens.

Choosing the right display technology is difficult, and depends on the application and usage context. Do not hesitate to contact us for information.

 

Logical and physical format

A passive 3D TV screen will send half of the scanlines to the left eye, half to the right eye. An active 3D TV will display the picture for the left eye and the picture for the right eye alternatively (alternate frames). The physical format required by these two kinds of 3D TV is different: for the passive set, the picture is interleaved in space, for the active set it is interleaved in time.

However, consumer 3D TV sets all offer features converting other input formats to their native physical format. For instance, they will normally all accept a video stream where frames are sent one after another (alternate frames). The passive TV set will send the first frame to the even rows, the second frame on the odd rows, and so on. This choice of logical format is made with the remote control of the TV set, using the 3D input menu.

There are logical formats that do not directlly correspond to a physical format. For example, many videos are available in side-by-side format, where the two pictures each occupy half of the frame. This is the format of the pictures generated by the Sony Bloggie3D.

 

Choosing the right logical format

All combinations of logical and physical format do not deliver the same picture quality. For instance, if you show a side-by-side video on a passive TV set, you will divide the horizontal resolution by two (because of the side-by-side format), and then again by two vertically (because each eye only sees every other scanline). If possible, it is better to use an "over-under" format where the vertical resolution is already divided by two, but there is no loss in horizontal resolution. The resulting picture will be sharper.

In general, the best quality will be achieved with alternate frames, since in that case two full-frame pictures will be sent to the display. With the right hardware, you can get true Full HD resolution with each eye. You can even go beyond Full HD, for example with digital cinema 4K projectors.

 

Graphic cards: "professional" or "consumer"

Unfortunately, there is another factor to consider here. The majority of consumer-grade graphic cards will not generate alternate frame signals for OpenGL applications. The corresponding feature, called "Quad buffers", is reserved by nVidia and AMD to their high-end professional cards.

This limitation applies to Windows PCs. Apple Macintosh computers generally offer support for Quad Buffer, except for the last generation of entry-level laptops equipped with Intel HD graphics.

Tao Presentations automatically detects whether Quad Buffer is available or not. If you see a menu entry called "Enable stereoscopy" in the command menu, or "3D (quad buffer)" in the View>Display mode menu, then you are lucky: your card supports OpenGL quad buffer, and you should be able to generate alternate frames.

 

Beware of the overscan

If you use a computer to generate a stereoscopic picture on a 3D TV, you also need to disable overscan. Overscan is a mechanism which crops and scales the picture, and is unfortunately enabled by default on most consumer HD TVs. As a result, one pixel sent by the computer no longer directly maps onto a pixel on the screen, even if the resolutions are 1920x1080 in both cases.

This mechanism gets in the way of stereoscopy, in particular for all geometric modes (side-by-side, over-under, interlaced). In that case, pixels for the left and right eye are no longer exactly where they should be, resulting in a blurred image, ghosting effects, or misaligned left and right eye pictures.

To use stereoscopy, it is critical to disable overscan both on the TV set and on the computer. The way to do that depends on the TV set and operating system. On most TVs, it is an option with a strange name, like "Just scan" on some LG TVs. On the PC and Macintosh, you can find the overscan adjustments in the control panel for the display.

 

Creating 3D content is fun

Understanding how 3D works is a bit complicated, but the reward is worth the journey. A real-time 3D display like the one Tao Presentations offers makes it easy to have fun exploring depth effects, whether with 3D objects or with movies, picture or text.

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