Courtesy of HDTV Magazine; Enjoy.
HDTV MAGAZINE'S WAVEFORM
BY
RICHARD FISHER
Viewing distance is critical.
The right viewing distance is critical for enjoying the full benefits of HDTV. What we seek is a distraction-free image large enough on our retina to deliver the illusion of reality. The wrong viewing distance will subtract or eliminate the immersive experience that High-def was designed to provide. Being either too close or too far can also create problems with imaging appearance and color. The wrong distance may even promote viewer fatigue.
Our old NTSC system was geared for 19" 4:3 images. You can watch that screen size at any distance. There is always a formula, however, for calculating just the correct viewing distance for any screen size and its corresponding resolution. This is called the critical viewing distance or CVD.
CVD is that closest distance you sit to your HD without seeing distracting artifacts. For NTSC to appear artifact free a viewing distance of 8 screen heights is required. This distance makes the picture, made up of scan lines and sampling points across the scan line, appear as a contiguous image. Both bias lighting and wall color/ room decor should be taken into account if you are to achieve accurate color perception of your video image. At 8 times PH the image of a 19 inch NTSC screen appears in a 10 degree field of view (FOV). To raise home video to the level of home theater a larger image FOV is required. THX recommends no less than a 26 degree FOV for the back row in a movie theater and 36 degrees as optimal. The SMPTE recommends a minimum of a 30 degrees.
To view an NTSC image on a 4:3 set using this 30 degree FOV recommendation an impossible viewing experience is created. The scan lines and other electronic artifacts makes such a close view of NTSC profoundly ugly. At that distance dark voids or lines are seen strewn across the entire screen.
Over the last 15 years folks have taken data grade projectors and scaling electronics (which converts one scan rate to another) to create huge pictures without the line structure being visible. Still, the amount of information in the image proved to be too little. The artifacts became less obvious, yes, but the resolution-starved image remained fuzzy. Many of us learned to ignore this lack of clarity while enjoying what little we could gain from this recipe.
HDTV was designed for artifact-free viewing from a 30 degree field of view. Two of the human visual system's ocular channels become stimulated from such a view much as woule be in real life. The detail-sensitive part of our vision ranges from zero (dead center on retina) out to 10 degrees. This "channel" is superb for perceiving detail but is poor at detecting motion. Motion detection is left to our peripheral vision, which extends from, and well goes beyond, the 10 degree FOV. When both "channels" of the human visual system are stimulated at the same time by moving images, the sense of reality in the viewer is greatly heightened. It was found from exhaustive study in Japan that anything under 30 degree failed to stimulate their test subjects and anything over 30 degrees produced no added affect. This 30 degree FOV was all that was needed for optimum human involvement, or so the test results indicated.
To achieve this "nirvana" a substantial increase (over NTSC) in image information (resolution/bandwidth) was required. In addition to highly sophisticated electronics new consumer displays had to be produced. These displays are kin to computer or data devices more so than to old NTSC television. Not only is the display to be artifact free at the CVD no digital artifacts (such as pixilation; contouring; blocking and "mosquito" noise) should be seen.
It was decided from those tests in Japan that the new television system had to be made up of at least 1000 scanning lines top to bottom and 2000 sample points across each scanning line (thus the 2 million pixels one hears so much about these days). These first specifications progressed in often contentious international committees to become the present 1080i X 1920 (which you now find for sale in your local retail CE store, and soon to be sold around the world). The 720p was derived as an equivalent image format to the interlaced 1080i..
We finally have a system that gives us a movie theater experience in our own homes. It is complete with accurate color, well defined and detailed images, and is devoid of visible picture structure as well as transmission-related artifacts.
The significance of HDTV resolution is tied to this all-important viewing distance.
HD requires a CVD of 2.5-3.2 screen heights. Beyond 3.2 screen heights you are wasting expensive resolution. If you are too far from the screen there is scant difference between HD and SD (with the exception of screen shape and newly achieved color accuracy). Sit closer than 2.5 screen heights and you likely become distracted by individual pixels and the line structure (and any other video goblins caused by the electronics and image parameters).
The chief aim of HD is to immerse the viewer into the program. You are made to feel at one with the HD image. This happens with a 30 degree FOV (30 degree from one side of the screen to the other). Like viewing an IMAX movie the viewing experience may not be comfortable for everyone. Motion in the moving images can produce a sea sickness. If this applies to you there is no solution other than to increase the viewing distance so that the stable room environment provides a fixed reference. This too can cause added problems, such as poor color perception and viewing fatigue. The better fix is bias lighting, which is covered in the next issue.
KEEP IT SIMPLE
If you ever wanted to create the movie theater experience in your home, you now can.
If the experience of HDTV is important to you then set the rule in your home for being at the right viewing distance. I have found that 3-4 screen heights is optimal. If that distance is not used don’t get wrapped up in resolution specs and concentrate on the display having at least one native HD scan rate--1080i, 720p or even 1080p, plus the HD screen shape of 16:9.
HDTV MAGAZINE'S WAVEFORM
BY
RICHARD FISHER
Viewing distance is critical.
The right viewing distance is critical for enjoying the full benefits of HDTV. What we seek is a distraction-free image large enough on our retina to deliver the illusion of reality. The wrong viewing distance will subtract or eliminate the immersive experience that High-def was designed to provide. Being either too close or too far can also create problems with imaging appearance and color. The wrong distance may even promote viewer fatigue.
Our old NTSC system was geared for 19" 4:3 images. You can watch that screen size at any distance. There is always a formula, however, for calculating just the correct viewing distance for any screen size and its corresponding resolution. This is called the critical viewing distance or CVD.
CVD is that closest distance you sit to your HD without seeing distracting artifacts. For NTSC to appear artifact free a viewing distance of 8 screen heights is required. This distance makes the picture, made up of scan lines and sampling points across the scan line, appear as a contiguous image. Both bias lighting and wall color/ room decor should be taken into account if you are to achieve accurate color perception of your video image. At 8 times PH the image of a 19 inch NTSC screen appears in a 10 degree field of view (FOV). To raise home video to the level of home theater a larger image FOV is required. THX recommends no less than a 26 degree FOV for the back row in a movie theater and 36 degrees as optimal. The SMPTE recommends a minimum of a 30 degrees.
To view an NTSC image on a 4:3 set using this 30 degree FOV recommendation an impossible viewing experience is created. The scan lines and other electronic artifacts makes such a close view of NTSC profoundly ugly. At that distance dark voids or lines are seen strewn across the entire screen.
Over the last 15 years folks have taken data grade projectors and scaling electronics (which converts one scan rate to another) to create huge pictures without the line structure being visible. Still, the amount of information in the image proved to be too little. The artifacts became less obvious, yes, but the resolution-starved image remained fuzzy. Many of us learned to ignore this lack of clarity while enjoying what little we could gain from this recipe.
HDTV was designed for artifact-free viewing from a 30 degree field of view. Two of the human visual system's ocular channels become stimulated from such a view much as woule be in real life. The detail-sensitive part of our vision ranges from zero (dead center on retina) out to 10 degrees. This "channel" is superb for perceiving detail but is poor at detecting motion. Motion detection is left to our peripheral vision, which extends from, and well goes beyond, the 10 degree FOV. When both "channels" of the human visual system are stimulated at the same time by moving images, the sense of reality in the viewer is greatly heightened. It was found from exhaustive study in Japan that anything under 30 degree failed to stimulate their test subjects and anything over 30 degrees produced no added affect. This 30 degree FOV was all that was needed for optimum human involvement, or so the test results indicated.
To achieve this "nirvana" a substantial increase (over NTSC) in image information (resolution/bandwidth) was required. In addition to highly sophisticated electronics new consumer displays had to be produced. These displays are kin to computer or data devices more so than to old NTSC television. Not only is the display to be artifact free at the CVD no digital artifacts (such as pixilation; contouring; blocking and "mosquito" noise) should be seen.
It was decided from those tests in Japan that the new television system had to be made up of at least 1000 scanning lines top to bottom and 2000 sample points across each scanning line (thus the 2 million pixels one hears so much about these days). These first specifications progressed in often contentious international committees to become the present 1080i X 1920 (which you now find for sale in your local retail CE store, and soon to be sold around the world). The 720p was derived as an equivalent image format to the interlaced 1080i..
We finally have a system that gives us a movie theater experience in our own homes. It is complete with accurate color, well defined and detailed images, and is devoid of visible picture structure as well as transmission-related artifacts.
The significance of HDTV resolution is tied to this all-important viewing distance.
HD requires a CVD of 2.5-3.2 screen heights. Beyond 3.2 screen heights you are wasting expensive resolution. If you are too far from the screen there is scant difference between HD and SD (with the exception of screen shape and newly achieved color accuracy). Sit closer than 2.5 screen heights and you likely become distracted by individual pixels and the line structure (and any other video goblins caused by the electronics and image parameters).
The chief aim of HD is to immerse the viewer into the program. You are made to feel at one with the HD image. This happens with a 30 degree FOV (30 degree from one side of the screen to the other). Like viewing an IMAX movie the viewing experience may not be comfortable for everyone. Motion in the moving images can produce a sea sickness. If this applies to you there is no solution other than to increase the viewing distance so that the stable room environment provides a fixed reference. This too can cause added problems, such as poor color perception and viewing fatigue. The better fix is bias lighting, which is covered in the next issue.
KEEP IT SIMPLE
If you ever wanted to create the movie theater experience in your home, you now can.
If the experience of HDTV is important to you then set the rule in your home for being at the right viewing distance. I have found that 3-4 screen heights is optimal. If that distance is not used don’t get wrapped up in resolution specs and concentrate on the display having at least one native HD scan rate--1080i, 720p or even 1080p, plus the HD screen shape of 16:9.
I feel so inadequate with my mere 55" (of course it is exactly half) LOL. 
