3D TV Viewing Distance Explained

What constitutes an optimum TV viewing distance for a 2D HDTV does not necessarily leads to an optimum 3D TV viewing experience in the home.

As we have stated in our discussion on 2D TV Viewing Distance, when it comes to standard TV viewing, the only factors that come into play when determining the optimum viewing distance relate only to the TV screen size and the screen resolution.
 

3D TV Viewing Distance and 3D TV Comfort Zone

In the case of 3D TV, one cannot determine the optimum 3D TV viewing distance simply by relating the viewing distance to the TV screen size and the TV screen resolution only. Keep in mind that the illusion of a third dimension in 3D TV causes the nearest point of the 3D image to appear closer to the viewer than the TV screen itself. Similarly, the farthest point of a 3D TV image appears farther away from the TV screen - this despite that the TV image is actually being displayed on a flat surface at a fixed distance away from the viewer.

In other words, a third factor comes into play that imposes its own constraints on the whole 3D TV viewing distance equation. This is what is referred to in 3D TV technology as 3D comfort zone.

As further explained in our article on 3D TV technology, there is a disparity in 3D TV - known as fundamental disparity - between the eye convergence point and the eye focusing point. This disparity is an unnatural event for the brain since in normal human vision, these two points reside at the same point in space. Move closer to the 3D TV screen and this disparity between convergence and focusing would increase, leading to a more aggressive 3D experience. Move further away and you will start losing more of the 3D impact in your 3D TV viewing.

Fundamental disparity in 3D is directly related to the left-eye/right-eye images separation, or image parallax. The value of the image parallax determines the aggressiveness of the 3D viewing experience. The audience 3D comfort zone refers to that parallax range which results in a 3D viewing experience that is easy on the viewer.  Exceed this comfort zone and the brain would start finding it hard if not impossible to properly fuse the left and right eye images into one 3D image. Should this happen, the 3D image would eventually appear as a blurred 2D-image. In some individuals, this may result in disorientation and even headaches.

So the whole issue when it comes to 3D TV viewing is: What is the optimal 3D TV viewing distance subject to the constraints associated with the 3D TV comfort zone? And how does all this impact the TV screen size and screen resolution?

Before delving further with our discussion on an optimal 3D TV viewing distance, it is important to realize that as in the case of 2D TV, 3D TV viewing distance is more a matter of personal preference. There are no strict and fast rules - but only recommendations.

At the same time, keep in mind that the constraints resulting from the 3D TV comfort zone imposes even stricter limitations as to where one can sit to enjoy 3D TV. In this respect, the recommendations details in this article should help you find that sweet spot for a more enjoyable and immersive 3D TV viewing experience in the home.

In the article on TV viewing distance already referred to above, we have stated that THX recommends maintaining the field of view between 26 degrees and 36 degrees for an immersive TV viewing experience. We have also shown how this translates to an optimum TV viewing distance that varies between 2.2 to 1.54 times the screen width.

In addition, we have shown that how much close you can sit to the TV screen depends on the TV screen resolution. The constraints resulting from visual acuity imply that the maximum viewing distance from a 1080p HDTV should be limited to 1.8 times the screen width; in the case of a 720p HDTV, this corresponds to 2.7 times the screen width.

Move further way from say from a 1080p HDTV than 1.8 times the screen width and you would no longer see the full picture detail supported by the 1080p higher pixel count. Similarly, move further away from a 720p HDTV than 2.7 times the screen width and the image content on your HDTV would soon start appearing the same as that from a standard definition TV! At the same time, move much closer to the TV screen than these recommended viewing distances and you risk seeing the image buildup structure - with the image taking a somewhat blocky or pixilated appearance, while image artifacts would become even more visible; this may eventually ruin an otherwise pleasing viewing experience.

So far so good for 2D TV viewing, but how does the new constraint resulting from 3D TV technology - the image parallax comfort zone - changes the whole equation when determining the optimal 3D TV viewing distance?

In our article on 'Is it Worth Investing in 3D TV Now - Challenges of 3D TV in the Home', we referred to a study by In-Three, Inc. This study shows that the comfortable parallax zone in 3D TV in the home shrinks to just 2-inches - from a positive 1 inch to a negative 1-inch for a viewer sitting 6 ft away from the TV.  In contrast, the parallax range for comfortable 3D viewing in the movie theater for a viewer sitting 40 ft away from the movie screen is 12.5 inches; this leads to a 3D image that appears as close as 8 ft away from the viewer, up to infinity.

The reduced parallax range in the case of 3D TV viewing is necessary as objects closer to the viewer exerts even more pressure on the brain to direct both the eyes converging and focusing muscles to the same spot in space.  This reduced parallax of just 2-inches in the case of home theater 3D corresponds to a nearest point in the 3D image that appears at 70% of the viewer to screen distance away from the viewer, to approximately 165% of the viewer-screen distance. This applies to a person sitting approximately 6 feet away from a typical medium size 55-inch to 60-inch diagonal screen.

We say medium size since despite the massive size 'per se' of say some of the latest 55-inch 3D LED LCD HDTVs, this still represents a relatively medium size screen for a truly immersive home theater experience. In other words, even at this screen size, the mind would still see the image as somewhat smaller than in real life; this in itself affects the mind's ability to get immersed into the movie action. A possible way out to partially solve this issue is to move closer to the TV screen. But to move closer to the TV screen means that you need to go for the highest resolution HDTVs - namely 1080p HDTVs.

This ability to get immersed into the movie action becomes even more challenging in the case of 3D TV content because of the fundamental disparity in 3D viewing between convergence and focusing.

This leads us to the conclusion that for the best immersive 3D TV viewing experience, there is the need to invest in a TV that has the biggest screen size you can afford for your viewing distance and to move closer to the screen as is practically possible.

If your budget does not allow and your room still allows for a bigger screen size, it is better to opt for a larger 720p HDTV (when available) than invest in a smaller 1080p 3D HDTV. But if both your budget and room size allow, the best way for an optimum 3D viewing is to invest in a 1080p 3D HDTV with the largest screen size you can afford.

Move close, but how close? In the home, the TV screen size remains relatively small in comparison to the screen at the movie theater. So to make up for the smaller TV screen size, one has to move closer to the TV to maintain an adequate field of view for an immersive 3D TV viewing experience.

Earlier on in our discussion, we stated that for an immersive 2D TV viewing experience in the home theater, THX recommends a range that varies between 1.54 to 2.2 times the screen width. We have to translate this into the optimum 3D TV viewing distance while remaining within the constraints as resulting from visual acuity and 3D TV comfort zone.

What turns this whole issue rather challenging is that in the case of a 3D image, there is no fixed distance of the image away from the viewer as in the case of 2D TV. Instead, you have two virtual extremes points within which the 3D image resides - a nearest virtual point and a farthest virtual point.

So... How can we arrive at an optimal 3D TV viewing distance when the 3D image does not reside at a fixed distance away from the viewer?

In our opinion, a possible way forward to help determine the best 3D TV viewing distance is to ensure that the average between these two virtual extreme points fall within the recommended THX recommendations for an immersive viewing experience, subject to visual acuity limitations for your TV screen resolution.

Let's take the study already referred to above carried by In-Three, Inc. for comfortable 3D viewing in the home as a basis for our analysis. In-Three found that a person sitting at a close distance of 72-inches away from a 60-inch diagonal HDTV (corresponding to a TV screen width of 52.3-inches for a 16:9 HDTV), the virtual nearest point for that viewer will appear at 51-inches away from the viewer; this is equivalent to 70% of the 3D TV viewing distance away from the TV screen, with the 3D TV viewing distance being the actual measured physical distance between the viewer and the 3D TV screen.  On the other hand, the farthest 3D image point will appear at 118.8-inches away from the viewer, or 165% of the 3D TV viewing distance farther away from the viewer.

This leads to a virtual average 3D image that resides at 85-inches away from the viewer - corresponding to 1.63 times the screen width. This is within both the THX recommendations for an immersive viewing experience as well as close to the limits associated with visual acuity for a 1080p image. But the 60-inch diagonal TV used in the analysis is physically at only 72-inches away from the viewer, or approximately 1.4 times the screen width for a 16:9 HDTV.

This leads to the conclusion that for an immersive 3D viewing experience in the home, one should sit closer to the TV than in the case of standard 2D TV viewing:

• For a 1080p HDTV, the optimum 3D TV viewing distance resides at around 1.4 times the TV screen width, or 0.78 times the distance as resulting from visual acuity for a 1080p screen.

• In the case of a 720p HDTV, the optimum 3D TV viewing distance corresponds to 2.1 times the TV screen width, or 0.78 times the distance as resulting from visual acuity for a 720p screen.

And what about the best viewing angle for 3D TV?

As you may have already noticed from this discussion, 3D TV viewing in the home presents a number of major challenges for the brain to successfully fuse the two slightly different images seen by the left and right eye into one 3D image. And there is even more! The viewer is not only restricted to what constitute an optimum 3D TV viewing distance, but also to what constitute an optimum viewing angle for a more realistic 3D TV experience. Why?

For the viewer to enjoy the best immersive 3D TV viewing experience in the home, one has to view the screen from an angle that matches the camera shooting angle used during filming. Since current 3D content is shot from a fixed head-on perspective, the line from your seating position to the screen should be such as to represent a perpendicular to the screen surface, i.e. your 3D TV viewing should be along the TV axis, for a zero degrees viewing angle. This represents the sweet spot for the most realistic immersive 3D viewing experience.

Move away from this sweet spot and the resultant 3D image will soon start to appear somewhat abnormal as the brain tries to make sense of images seen by the left and right eyes - shot from head-on but that are being viewed at an angle. The brain would expect to see a side view not a head-on view when viewing images from the side.

This implies that if you really want to make the best out of the latest 3D TV technology and get the best out of your new and expensive 3D HDTV, you should not only stay at a closer 3D TV viewing distance than is typical for 2D TV viewing, but also limit your TV viewing angle to as close as possible to zero degrees along the TV axis.

In summary...

To enjoy the best 3D immersive experience in the home, you need to move closer to the TV and invest in the largest screen your budget and you room layout allow. In particular, a closer 3D TV viewing distance would help enhance an otherwise mild 3D experience in the home in comparison to the more aggressive 3D in the movie theater. This significantly less aggressive 3D experience in the home results from the reduced parallax necessary to remain within the 3D comfort zone when shooting 3D content for home viewing.

Equally important, ensure that the seating layout is as close as possible to the zero degrees along the TV axis. The latter is not possible with multiple seating but limiting the number of seats should help ensure that each viewer will still enjoy a great 3D TV experience.

The optimum 3D TV viewing distance for a 1080p HDTV stands at 1.4 times the screen width - just slightly closer than the 1.54 resulting from the THX recommendations for an immersive TV viewing experience. In the case of a 720p HDTV, the optimum 3D TV viewing distance is approximately at 2.1 times the TV screen width.

If you find these distances a bit too close for your liking, just move a little farther away but try to remain within the 1.54x the TV screen width for 1080p HDTVs and 2.7x for a 720p HDTV.

We believe that the above recommendations for 3D TV viewing distance should help you arrive at an optimum viewing position for a most immersive and enjoyable 3D TV experience. However, remember that TV viewing distance is more a matter of personal preference. Therefore...

Do not be afraid to experiment with your 3D TV viewing distance to find the best spot for your liking.