Projector Reviews

3D Video – A Little History

This post is intended to provide a little history for 3D video and to also provide some context for my prior blog on the 3D signal formats that are defined by the HDMI version 1.4a specification and for Blu-ray 3DTM.  I hope that it will also provide some context for future blogs and discussions related to 3D video.

As a little bit history, 3D using the anaglyph technique has been used with television for decades.  This technique requires the viewer to wear eyeglasses using colored lenses (e.g., one red and the other cyan) and this is an inexpensive method to display 3D content with any standard color TV or video projector.  Virtually all consumer video sources (i.e., DVD, Blu-ray and TV broadcasts) offered in 3D prior to 2010 used the anaglyph technology for creating the 3D effect. However, as many of you have probably experienced yourself, the anaglyph technique produces poor results when trying to view video in color and is subject to “crosstalk” between the images intended for the right and left eyes.  Note the commercial movie theaters since the 1950’s have typically used different polarization for the projected light to separate the right and left image streams along with polarized 3D glasses to provide a superior 3D effect.  However, this technique was not appropriate for consumer video as it is not compatible with conventional CRT TV displays.   Below is an illustration typical of the cheap, disposable, paper frame anaglyph glasses provided for viewing 3D videos that use the anaglyph technique.

Typical Anaglyph 3D Glasses

As CRT-based video projector technology evolved during the late 1980’s and 1990’s models appeared, from such companies as NEC, that would accommodate the higher resolutions and refresh rates needed to make them suitable as computer displays.  During this same time period the technology for using liquid crystals in glasses as shutters for 3D viewing emerged in the engineering/scientific community.  These systems work by alternately displaying the images intended right and left eyes and with the 3D shutter glasses synchronized to alternate which lens of the glasses become transparent while the other lens became opaque.  Just over a decade ago PC graphics chip manufacturer Nvidia, partnered with several graphics card manufacturers, introduced a new generation of PC graphic cards (GeForce2) along with software drivers and 3D shutter glasses.  By the time the Nvidia 3D-enabled video cards and glasses appeared there were a number of projector manufacturers offering models that provided sufficiently high refresh rates to support 3D.  I used a Sony VPL-G70 projector at that time that would support a 120 Hz vertical refresh rate which allowed computer generated 3D-video to be presented to each eye at 60 Hz. (the same as with most of the current 3DTVs).  However, there was no source for 3D movies or TV programming compatible with this setup at that time (i.e., there were only a few video games and some business/scientific applications).

I don’t recall any of these CRT projectors specifically being advertised as being “3D Ready.”  A new generation of 720p DLP front projectors appeared about 3 years ago with the “3D Ready” label that essentially offered 3D support in the same way as the earlier generation of CRT front projectors.  They were intended to be connected to a properly configured (both hardware and software) PC that could output 3D at 120 Hz, as a sequence of alternating right and left images.  These first generation of 720p DLP “3D Ready” projectors were functionally equivalent to certain 3D capable LCD flat panel computer monitors in that also supported a 120 Hz vertical refresh rate.  Such projectors and monitors might more appropriately be considered “3D PC Ready” since a PC was the envisioned source of the 3D signal.

After 3D started making a significant resurgence for commercial movies a few years ago, several of the consumer electronics manufacturers saw the opportunity to bring 3D into the home for more than gaming.  The two industry organizations most involved in developing the industry standards for this new generation of 3D were the Blu-ray Disc Association (BDA) and the HDMI Licensing, LLC, on behalf of the HDMI Founders.  The BDA developed technical standards to enhance the capability of this HD disc media to also support 3D.  The Blu-ray 3DTM specification was released to BDA member companies in late 2009.  The technical specification for a new generation of HDMI with the 3D enhancements (i.e., version 1.4a) was released in March 2010.  Both the Blu-ray and HDMI 3D related enhancements were coordinated to ensure they were consistent with each other.  The more all-encompassing of these specifications is the HDMI version 1.4a (HDMI 1.4a) as it addresses both video sources as well as video displays. 

Lacking any industry 3D standards, older display implementations in support of 3D, including those earlier CRT projectors and the newer DLP 720p “3D ready” projectors, had placed the burden on the video source to produce a signal in the format that was supported by that display.  This generally meant the 3D signal had to be provided by the source device with sequentially alternating right and left frames and with a fixed vertical refresh rate (e.g., 120 Hz).   However, the HDMI 1.4a specification took a substantially different approach for 3D support in consumer products.  Rather than placing the burden on the 3D source device to provide the 3D signal in the format required by the display, the new HDMI 1.4a specification has placed the burden on the display device to accept any of the set of 3D signal formats defined as required by that standard.  For source devices (e.g., a Blu-ray player, cable TV box, etc.) the HDMI 1.4a specification only requires that the 3D signal be provided in any one of the signal formats defined as required by that standard.  The Blu-ray 3DTM specification then defines for Blu-ray 3DTM players which one specific 3D format, from the HDMI 1.4a specification, is required.  With this approach the display device (e.g., projector) is required to accept the 3D signal in any of the formats defined as required by the HDMI 1.4a specification and to then decode and process this into whatever format that specific display requires for displaying the 3D video.  Further, it is entirely the responsibility of the display device to apply whatever technology is uses to create the separation of the right and left images streams (alternating images and use of shutter glasses, polarization, etc.). Thus the older pre-HDMI ver. 1.4a approach was based on dumb displays/projectors and smart video sources (e.g., PCs).  Now the new approach defined in the HDMI ver. 1.4a specification calls for smart displays/projectors and dumb 3D sources.  That is the origin of the incompatibility that results from trying to connect one of the pre-HDMI 1.4a (i.e., dumb) projectors to one of the new HDMI 1.4a equipped 3D sources (e.g, Blu-ray 3DTM player).  In this case such a dumb-and-dumb(er) configuration will not produce a brilliant 3D result (actually no 3D).

 RonJ  (Ron Jones)