Optimum HDTV viewing distance

HDTV is designed to provide an experience more realistic than the television system it is designed to replace. The "thrilling realism" HDTV attempts to offer arises from increased resolution (detail) and the typically large screen sizes. A larger display increases the visual angle at which content is viewed, both of which contribute to an increased feeling of presence. Thus, the correct viewing distance is critical to the enjoyment of HDTV as it is intended. While helping to define the HDTV standard, RCA engineer and member of the US delegation to the International Telecommunication Union-Radiocommunication Sector (ITU-R), Bernard J. Lechner, made an early analysis of viewing distance, deriving the so-called Lechner distance. This approach, based on the limits of the human eye, can be used for all resolutions (including future resolutions). This is the "optimal viewing distance" found in the ITU-R. Visual angle The optimum viewing distance is affected by the horizontal angle of the camera capturing the image. One concept of an ideal viewing distance places the viewer where the horizontal angle subtended by the screen is the same as the horizontal angle captured by the camera. If this is the case, the angular relationships perceived by the viewer would be identical to those recorded by the camera. A mismatch in this regard is traditionally disregarded, but some rotating motions can make these distortions very noticeable as a pincushion effect. This is likely in 3D video games, so gamers are likely to adopt close viewing positions matched to a game's fixed field of view. If the camera's angle were always the same, an ideal viewing distance could be easily calculated. However, the camera's horizontal angle varies as the focal length of its lens changes. If the camera's sensor has fixed dimensions, a shorter focal length (wide angle) lens captures a wider angle of view, requiring the viewer to sit closer to the screen. Conversely, a longer focal length (telephoto) lens captures a narrower angle of view, demanding a more distant viewer position. Such opposing viewing distances would not only be impractical, but would negate the very purposes of telephoto shots (for example, to see a distant object in more detail, or minimize distortion in facial images) and wide-angle shots (causing the viewer to sit too close to the screen, where undesirable image artifacts would be visible). One compromise assumes the lens is "standard" (a 50 mm focal length, for a standard 35 mm format). A "standard" lens preserves the same spatial relationships perceived by a spectator at the camera location. For a "standard" lens image, viewing distance should be equal to the diagonal length of the screen. It has been demonstrated that viewing a display that occupies a greater visual angle (also referred to as field of view) increases the feeling of presence. Angular resolution With printed graphics, resolution refers to the number of pixels (usually referred to as "dots") in a fixed linear measurement. With HDTV, resolution is measured in terms of the number of pixels in the physical display. When the resolution of a printed image is increased, the image is cleaner, crisper and more detailed. However, image quality does not improve if the increase in resolution exceeds the observer's visual capabilities. For an HDTV's image to noticeably improve, its resolution per degree of arc (or angular resolution) must increase as well as the pixel count of the display. == Recommendations ==

To maximize the feeling of presence and thus provide a better viewing experience, the viewer would need to be situated at the theoretical spot where the HDTV occupies the widest view angle for that viewer. It is also important that the resolution of the display per degree of arc remain at a high quality level. Opinions regarding where the ideal position lies are numerous and varied. Recommendations on HDTV viewing distances fall into two general classes; a fixed distance based on HDTV display size, or a range of distances based on the display size. The most common recommendations from reasonably authoritative sources are presented below. Fixed distance Fixed distance recommendations are the more common of the two types. For the most part, the majority of the fixed distance recommendations were issued before the end of 2007, when arguably HDTV displays were still in the early adoption phase. The concept of optimal viewing distance, is based on the limits of the human eye, i.e. its angle of resolution. This is its ability to distinguish between two pixels. For normal visual acuity (6/6 vision), this angle is 1 arcmin. To obtain a fixed distance for a given resolution, it must be expressed in picture heights (H). Please note! The optimal viewing distance is not suitable for designing a user interface; It is the distance actually observed in households that should be used. It is much greater than the optimal viewing distance and highly variable. Diagonal measurement × 2.5 (corresponding to 20-degree viewing angle) One of the more popular recommendations on the proper HDTV viewing distance is multiply the diagonal measurement of the display screen by 2.5. This recommendation is cited by television manufacturers, retailers, respected publications and websites, though the popular electronics review website CNET suggests that high-resolution content can be watched at a closer distance – 1.5 times the display screen's diagonal measurement (corresponding to 32 degree viewing angle). × 1.6 (corresponding to 30-degree viewing angle) Viewing an HDTV from a position where the display occupies a 30-degree field of view is widely quoted as the SMPTE (or SMPTE 30) recommendation (equivalent to about 1.6264 times the screen size in a 16:9 TV). This recommendation is very popular with the home theater enthusiast community, appears in books on home theater design, and is also supported by a white paper produced by Fujitsu. Although an article on research into setting the specification for the next evolution of HDTV, Ultra HDTV (or UHDTV), does support the premise that HDTV was optimized for a view angle of 30 degrees, (the actual angle is 40.04 degrees). Their recommendation was originally presented at the 2006 CES show, and was stated as being the theoretical maximum horizontal view angle, based on average human vision. In the opinion of THX, the location where the display is viewed at a 40-degree view angle provides the most "immersive cinematic experience", the technically adventurous and the sports enthusiast looking to have the ultimate viewing experience. Today, the typical HDTV consumer's aims may be a little more modest; total immersion takes a back seat to room integration. Major retail chains like Best Buy that once stated their recommendation as a fixed distance, Manufacturers have also started to provide range recommendations, updating their websites with small applications that denote the optimum viewing distance as a range of distances. THX in March 2009 added range recommendations to their website. Retail recommendations The recommendations currently posted on the websites of retailers Best Buy and Crutchfield take more of a middle ground. Both retailers post a minimum viewing distance that accommodates a view angle of just a little over 32 degrees on average. This viewing distance approximates the view angle needed to be able to see pixel level detail. The maximum viewing distance will provide a viewing angle of approximately 16 degrees with Best Buy's recommendation and approximately 20 degrees with Crutchfield's. The maximum viewing distance (minimum viewing angle) provided by Best Buy aligns with vision theory on the highest spatial frequencies perceivable by the human visual system. Crutchfield's maximum viewing distance aligns with the lower boundaries where viewers typically begin to find HDTV immersive. ==Factors influencing the calculations==

Each recommendation serves the underlying goal of the organization that proposes it. Manufacturers will have an easier time selling their HDTVs if they support a position that does not require consumers to purchase as large a set as required by the THX recommendations. In the absence of economic influences, calculating the best screen-size-to-distance ratio that will produce the utmost feeling of presence is not at all straightforward. There are a number of factors that can affect the calculation including the limitations of the human visual system, by a person with normal vision. An arcminute is an angular measurement, which is equal to 1/60 of one degree of a circle. Normal vision is referenced as 20/20 vision in North America, the British Isles, and 6/6 vision in continental Europe respectively. The visual acuity threshold has been identified as a constraint factor in the recommendations on the optimum viewing distance for HDTV, Assuming display is flat, with 1 arcminute as the constraint for seeing critical detail, in order not to miss any detail a viewer would need to be situated at a position where their view angle to a 1080p HDTV is approximately 31.2 degrees or greater (32 degrees for spherical display), for 2160p HDTV approximately 58.37 degrees or greater (64 degrees for spherical display) and for 4320p HDTV approximately 96.33 degrees or greater (128 degrees for spherical display). Also, there is the issue of vernier acuity, which is the eye's ability to detect an offset between 2 lines and stereoacuity, which is the ability to discriminate depth by the use of both eyes. Vernier acuity and stereoacuity are cited as being detected with only a 2–4 arc second degree of separation. Ultimately all of the various types of acuity play a part in how we see things and more importantly, how we perceive what we are witnessing. The complexities of the human visual system and the relationship between different types of acuity are not yet fully understood. Even with different HDTV display technology, such as front or rear projection DLP, LCoS or laser TV, the way HDTV images are rendered limits how close a viewer can be before the image's segmented nature becomes evident. HDTV displays produce images the same way computer bitmaps (also known as raster graphics) are produced, using a mosaic of colored 4-sided pixels. Like computer monitors, each HDTV display has a video resolution consisting of rows and columns of specific numbers of pixels. From far enough away, the human eye perceives the illuminated pixels as a smooth image. Consequently, optimum viewing distance recommendations based solely on human visual system and technological limitations may not always produce the best viewing experience. Viewers with lower visual acuity, who prefer to watch HDTV without their corrective lenses may want to sit closer to see critical details and run the risk of undesirable side effects. End-user content selection Although studies show the feeling of presence and image size are directly correlated, calculating the size to viewing distance relationship may not be a necessary exercise for all consumers. A 1997 study, which hypothesized that increases in screen size would give rise to increased feelings of presence, found that the content was more important than the screen size. The findings were that for commercials, action-adventure and reality programming an increase in the feeling of presence did correlate with increased size. The researcher attributed these findings to the fact that the aforementioned content contained scenes that were shot with a point of view camera, scenes with sudden movements and shorter shots. Conversely, for programming consisting of talk shows and drama programs changing the screen size had no effect on the feeling of presence. == See also ==