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How Do 3D TVs Work?

How Do 3D Televisions Work?

Before we begin, let's take a closer look at the dynamics of a 3D TV. Stereoscopy, or 3D imaging, does not entail rocket science, but it calls for a bit of cunning and trickery in order to fool your brain into seeing a 3D picture. Fundamentally, stereoscopic images appear blurred when viewed with naked eyes. That's because the display is sending two sets of images, one for the left and the other for the right eye. When applied with the right type of eyewear (depending on the 3D technology used), these two images are combined by the brain which then interprets them as a single image with depth. These left and right images are typically shot on cameras with discrete lenses, spaced marginally apart to create a slightly different perspective. Alternatively, a conventional 2D film can be post-processed to create left and right eye pictures.      

In the past, flatscreen displays did not make suitable candidates for 3D due to their slower frame rates. For example, a 50Hz TV can only yield 25 frames per second (for each eye) at best. It is unlikely anyone would enjoy flickering 3D images, would they? Thankfully, the AV landscape has evolved dramatically since then. With native 100Hz or 120Hz frame rates (do not confuse this with pixel response time) being a reality now, manufacturers are empowered to develop functional 3D screens for the consumer end. As we speak, however, TV makers are still in the process of tweaking their offerings to bring the stereoscopic experience one step closer to perfection.


3D Formats: Frame Packing vs. Top-and-Bottom vs. Side-by-Side

Not all the 3D content are the same; some come from original 3D sources, some are recreated from 2D. For most consumers, the best 3D content will be those from Blu-ray Discs. Typically encoded at 1080/24p, they employ a method called frame packing, which in layman's terms, is the stacking of two 1,920 x 1,080 images (with some spacing in between) one atop the other. (This creates a tall 2,205 x 1,920 image that you don't actually see.) The 3D image quality is high simply because each eye gets a full HD image.

Due to bandwidth concerns, frame packing is not favored for cable and over-the-air 3D content. In fact, most broadcasters stick to 1080i in order to strike a balance between the need to offer their viewers HD quality content and the need to increase the number of HD channels or streams. In most of these cases, they will try to have the two images needed for each eye be merged into a single image. There are two main ways of doing this: top-and-bottom and side-by-side.

As the name implies, the top-and-bottom method uses either two 1,280 x 360 (for 3D in 720p) or two 1,920 x 540 (for 3D at 1080/24p) images, one on top of the other. The side-by-side method is similar, just that it's now the horizontal (instead of vertical) resolution that's halved. In other words, each eye will get either a 640 x 720 or a 960 x 1,080 image. While some may say that the top-and-bottom method is better for sports content, at the end of the day, neither offers very high image fidelity due to the often noticeable drop in resolution.