To get the most from your home entertainment investment, achieve the best image fidelity from the programs you enjoy, and enhance your viewing comfort, incorporate the SMPTE recommendations into your viewing environment.
What's Robbing Your TV's Best Picture?
Alan Brown | CinemaQuest, Inc.
AN UNDETECTED CRIME:
I love movies! Theatrical motion pictures are a principle source of enjoyment and entertainment for myself and my entire family. I also enjoy helping other people experience this type of entertainment in their homes. Those are big reasons why I became a home theater professional.
Movies are a legitimate art form. A well-produced motion picture has the potential to inspire, delight, amuse, startle and temporarily transport an individual to another time and place. Movies tell a story but don't just appeal to the mind. The visual and auditory dynamics enhance and empower the drama, beauty and impact of the story being told. Great detail and care is exercised in the production of a cineplay to augment the storytelling with visual and auditory cues appropriate to the kind of emphasis desired by the director. "Realism" is conveyed when coupled with the audience's "willing suspension of disbelief." Time can seem to stand still when we are undistracted and captivated by the performance that is telling the story.
The art of home theater design and installation is to provide a fully integrated system that provides picture and sound fidelity, with a minimum of distracting elements. When consumers purchase the equipment for reproducing movies in their home they deserve the best performance possible from their sizeable financial investment. A movie's producer desires the intended audience to experience what he or she sees and hears in the screening room. Image and sound fidelity in a home theater means the audience experiences what the program producer originally intended.
This article will focus on the imaging side of the equation. Sound fidelity is a huge subject deserving its own discussion. I intend to focus on a segment of image reproduction far too frequently ignored in home theater design. An endless variety of articles are published about the hardware available for reproducing moving pictures in the home. Certainly the video display is a critical component in any system designed for home cinema. However, two components are frequently ignored or are insufficiently understood. The two critical components common to every home theater system I'll discuss in this article are the room and the viewer.
In the mid-1980s the Society of Motion Picture and Television Engineers (SMPTE- commonly pronounced simp'-tee) re-evaluated and revised imaging industry standards and practices for the use of electronic displays in the professional community. A segment of focus, pertinent to this article, was their work on human factors. They were concerned about the physical and perceptual affects that viewing conditions had upon technicians performing critical analysis of video programs for hours on end. SMPTE found that room decor and lighting impacted the viewer's ability to see the image correctly, and affected viewing comfort as well. They discovered that standardizing video monitor viewing environment conditions helped maintain production quality and consistency all along the production chain. Image fidelity was preserved and eyestrain or viewing fatigue was minimized. Regular calibration of the monitor for image accuracy was not enough to ensure consistent program quality. The room decor and lighting affected the viewer's perception of the image on the screen. A scientific study of the human visual system has shown that surrounding colors and ambient lighting can skew or alter a person's perception of the primary object of focus.
SMPTE's human factors research resulted in their Recommended Practices document #166: 'Critical Viewing Conditions for Evaluation of Color Television Pictures.' This publication (SMPTE RP166) defines various monitor settings, screen size/viewing distance, coloration of surrounding surfaces, viewing angle, and color of ambient lighting. It also specifies the location and intensity of room lighting, as it relates to the image on the screen.
How does all this relate to the home theater? Imaging science principles practiced in professional monitor environments also are beneficial in a home system. This is due to the common elements of human perceptual characteristics.
Room color specifications in SMPTE RP166 are as follows. Visible surfaces that surround the TV screen should be a truly neutral color. SMPTE used the Munsell Color Order System to define their color references. Neutral is any color of gray throughout the range from black to white. Surface colors that lie within the observer's field of view with the monitor screen should be in the neutral category. The purpose for this specification is to preserve accurate color perception of the image on the screen.
When we view a picture that is surrounded by color, that color is partly subtracted from our perception of the central object of focus. This is a characteristic of how our brain interprets the information sent to it by our eyes. In other words, a video image on a TV that has a red wall behind it will appear to have less red content in the picture. An aqua (blue-green) dress against a blue wall will appear more green. The same garment against a green background will appear more blue. Our perception of the aqua object would be unaltered, if the wall was neutral.
Skilled professional photographers, cinematographers and videographers are very sensitive to this phenomenon when composing a shot with a person's face against a colored background. Skin tones vary widely, as will the makeup used for a shot. Both backgrounds and wardrobe can flatter and compliment a certain type of complexion, or they can conflict. This effect can be substantial or subtle depending on how vivid the nearby coloration is. The best way to enhance and preserve the accurate perception of the natural coloration of an observed object is to provide a neutral colored surround. True neutral colors reflect light evenly across the color spectrum. In other words, a neutral surface will not alter the color composition of light reflected by it.
SMPTE also recommends the use of nearly neutrals for the rest of the surfaces in a video monitor environment. Munsell's nearly neutrals are colored pastels of various values from dark to light. Vivid colors are to be avoided anywhere in the room except for minor accents. This methodology is explained as serving to provide an environment that will help the technician's color perception adapt to a more neutral frame of reference. The human visual system takes some time to adapt to a new environment or lighting condition. Our eyes do not respond instantly to changing conditions. This characteristic is referred to as "persistence of vision."
The lighting used in a critical monitor environment was also an important issue addressed by SMPTE RP166. That document recommends using a type if illumination as close to "CIE D65 " as possible. In "color speak" this is a very specific color of white light. Video monitors are calibrated to maintain this "white point" as a standard of performance. Television images are composed of varying amounts of red, green and blue light. Our human visual system works on the same "RGB" basis. The color composition of white light produced by a video display is the foundation of how all the other colors will appear in the picture. Using a different color of light in the room, other than that produced by the monitor, subtly alters the technician's perception of the image on the screen. Standards are maintained in every video production environment to assure consistent results, regardless of where or by whom the work is performed on a video program. This methodology promotes accuracy, repeatability and fidelity of the original program throughout the evolution of its production.
The final link in the production chain for a video program is the TV being viewed by the intended audience. If the SMPTE standards and recommendations are faithfully adhered to and practiced by the video consumer, image fidelity will be experienced. Any departure from this methodology will result in an altered picture, as perceived by the viewer.
Other lighting recommendations in SMPTE RP166 pertain to the location and intensity of the ambient lighting used in the viewing environment. SMPTE specifies the location should be from behind the frontal plane of the monitor screen. Essentially, the light would reflect off the neutral colored wall behind the display. This orientation prevents screen glare and reflections that would contaminate or obstruct the picture on the monitor. The intensity of illumination is specified to be less than 10% of the brightest white produced on the screen. This condition serves to reduce eyestrain and viewing fatigue.
Viewing a typical TV program in a darkened room causes the iris muscles to contract and expand dramatically and frequently as the level of light on the screen changes with program content. Our iris forms the pupil, which regulates how much light is allowed to reach the retina. As our eyes become adapted to a dark room, the retina becomes more sensitive. Bright portions of a program can seem much brighter than normal. The amount of light produced throughout a typical TV show varies widely and changes frequently. A good demonstration of this behavior is to turn all the lights out in the room, face away from the TV and observe how much the light changes in the room during the program. This effect often resembles a room illuminated by a flashing strobe light. Providing some ambient light in the room moderates or "biases" the range of motion of the iris muscles. This technique is commonly known as "bias lighting." Eyestrain and viewing fatigue can be substantially reduced using this technique. No current self-contained video display on the market can produce its best picture in high ambient light conditions. Light striking the screen washes out the image and causes reflections. That's why many people intuitively prefer watching TV in the dark. However, televisions are often viewed during daylight hours. Manufacturers have to design TVs that are bright enough to provide a satisfactory image in high ambient lighting conditions. This only exacerbates the intensity of the image when the TV is viewed at night or in a darkened room.
Professional monitors are calibrated to produce 30 footLamberts of illumination at peak white. Most consumer TVs come from the factory with light output that is several times this figure. Bias lighting has proven to be even more needful for consumers. This technique was actually used in homes as far back as the 1950s. How many of us in our youth were told by our mothers that it's bad for our eyes to watch TV without a light on in the room? Many people leave some light on because they sense intuitively that it reduces eyestrain. SMPTE discovered that less than 10% ambient light was the ideal ratio. They also verified that using the same color of white light being produced by the TV preserved correct color perception. Providing a neutral wall color for the light to reflect from retained the light's color composition.
Various consumer video magazines have written about bias lighting in recent years. They have advised their readers to build their own from small fluorescent fixtures with "daylight" lamps rated at 6500 Kelvins. This color of fluorescent lamp can be near the CIE D65 white point mentioned in SMPTE RP166. The "color rendering index" or CRI rating of the lamp should be as close to 100 as possible. They also mention using neutral-density theatrical filter gel material to cover the lamp and dim it down to the 10% recommended level. These components can be difficult to locate for many do-it-your-self-ers.
My company has developed and marketed pre-assembled, high quality, bias lights over the last 6 years for both professionals and consumers. We have become the world leader in ideal viewing environment technologies and solutions. If you want the best pictures from your home theater display, the right room conditions are a vital consideration. Our web site offers relatively inexpensive solutions that help any videophile or movie lover improve their viewing experience. To get the most from your home entertainment investment, achieve the best image fidelity from the programs you enjoy, and enhance your viewing comfort, incorporate the SMPTE recommendations into your viewing environment. Stop being victimized by conflicting video viewing environment conditions in your home. View your TV in its best light by following these simple recommendations.
Best regards and beautiful pictures, Alan Brown, President CinemaQuest, Inc. www.cinemaquestinc.com
© 2005 CinemaQuest, Inc.
This post does not have any comments. Be the first to leave a comment below.
Post A Comment
You must be logged in before you can post a comment. Login now.