The Importance of Bias Lighting When Viewing in a Reference Environment

Discussion in 'Displays' started by Gregg Loewen, Mar 30, 2009.

  1. Gregg Loewen

    Gregg Loewen Video Standards Instructor, THX Ltd.
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    Just thought I would start a thread to discuss this very important topic.
     
  2. GeorgeAB

    GeorgeAB Second Unit

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    Gregg is correct in emphasizing the importance of bias lighting. However, the benefits apply to just about ANY electronic display environment where optimum picture quality and viewer comfort is desirable. Even non-reference viewing environments have problems that properly implemented bias lighting solves. Perhaps a better title would have been, "The Importance of Bias Lighting When Viewing Televisions." This technique has been used in video mastering suites for decades, for very specific reasons that relate to image quality and viewing comfort.

    My company has become a world leader in providing education and developing practical solutions for this topic. I intend to expand this thread as time goes by with more details. A good initial tutorial on the technical issues underlying the need for bias lighting can be found here: CinemaQuestv2.0 . Most central to this topic is the human factors research conducted by the Society of Motion Picture and Television Engineers (SMPTE), and others in the imaging sciences around the world.

    Any serious study and discussion of home theater must be founded upon imaging science. There are real and essential principles that support good viewing. Authentic image quality follows certain rules. totally independent of personal preference on the part of the individual viewer. This often is a revelation to the average consumer. As we explore this topic, each reader should find ways to improve the viewing experience in their video system.

    Best regards and beautiful pictures,
    G. Alan Brown, President
    CinemaQuest, Inc.
    A Lion AV Consultants Affiliate

    "Advancing the art and science of electronic imaging"
     
  3. GeorgeAB

    GeorgeAB Second Unit

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    I would be very interested in the impressions from forum members who have actually read the document linked to in my last post. Is this information largely new to you? Have you considered making changes to your TV's viewing environment to enhance your viewing experience? Do you consider convenience more important than a further pursuit of ultimate picture quality? Do you agree that conflicting viewing conditions can diminish the performance of a display?
     
  4. Clinton McClure

    Clinton McClure Casual Enthusiast
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    As always, a very informative read, George! And spot on from what I've seen. Folks would not believe how their eyes can play tricks on them with different ambient lighting conditions, background wall colors, items sitting close to the display, etc...

    My HT is nowhere near the ideal viewing environment, but it is also the living room and has to remain practical in the eyes of my better half. Oh, well... perhaps somewhere down the road I will be able to buy a house with a dedicated HT room or build one. Until then, compromise is the name of the game.

    Still, though, this is something all serious HTFers would do well to read, if for nothing else than for informational purposes. [​IMG]
     
  5. GeorgeAB

    GeorgeAB Second Unit

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    Informational purposes? Yes, as in how to minimize compromises (with their associated consequences to viewing enjoyment), which is difficult if you don't even know what video industry best practices are. Most video consumers just guess.
     
  6. GeorgeAB

    GeorgeAB Second Unit

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    The use of the technique of bias lighting has the perceptual effect of improving the contrast performance of televisions. Improved contrast in an image also has the beneficial effect of making the image appear to have greater sharpness.

    I was reminded of these benefits while reviewing an article from the 'SMPTE Journal,' November of 2002. The title of the article was 'The Importance of Contrast and its Effect on Image Quality' by Segler, Pettitt and Kessel. Here are some pertinent quotes from the article:

    "Contrast could be considered to be the most significant quality that impacts not only the perceived depth of an image, but also affects the apparent sharpness.....While the luminance level of a given image affects how the eye perceives contrast and detail, the ambient conditions surrounding the image can also have a dramatic impact. This phenomena was studied by Bartleson and Breneman (1967) to examine the impact of perceived contrast based not only on the luminance level of the image but taking into account the surrounding ambient luminance levels as well. Their results showed that the perceived contrast increased as ambient luminance increased. With the increase in ambient luminance, the eye interprets black levels as being darker while the impact to the white level is minimal. Since the perceived difference in dark areas is greater under the higher ambient luminance conditions, the perceived contrast is higher. It is a natural tendency to want low ambient luminance levels to strive for "better" perceived image quality and what is thought to result in higher contrast. However, in reality, the opposite is true. This tendency may be justified for current direct view CRT televisions due to the issue of glare that results from the glossy surface of the glass tube [also true for certain flat panel displays today]. With less ambient luminance, the glare is reduced- but it may be important to keep some ambient luminance behind the television [as in the case of bias lighting] to keep the perceived contrast higher.....While sharpness can affect the apparent contrast of an image, the converse is true in that contrast can also impact the apparent sharpness of an image. Images that have lower contrast will appear to be not as sharp as an image of the same content, but with higher contrast.....A subjective study was then conducted to verify the impact that ambient lighting has on perceived contrast. Several non-technical (and thus presumably non-biased) and technical observers were asked to compare a series of images with various ALL [average luminance levels] under different ambient luminance extremes in order to understand the impact that ambient viewing conditions might have on the perceived contrast between the two television technologies [CRT and DMD (DLP RPTV)]. Under dark ambient conditions, the result for images with an ALL > 5% was found to be equal between the CRT and the first DMD display. However, under bright ambient conditions (about 250 nits of luminance on the wall behind all of the units), the DMD display was favored over the CRT by 50% of the observers as having higher perceived contrast.....This proved that ambient conditions have the effect of potentially raising the black level threshold of the eye above the actual black level of the television such that the perceived contrast ratio is higher."

    Here's another related reference from: 'Color Appearance Models,' by Mark D. Fairchild, Ph.D., of the Chester F. Carlson Center for Imaging Science: Munsell Color Science Laboratory.

    "Their experimental results, obtained through matching and scaling experiments, showed that the perceived contrast of images increased when the image surround was changed from dark to dim to light. This effect occurs because the dark surround of an image causes dark areas to appear lighter while having little effect on light areas (white areas still appear white despite changes in surround). Thus since there is more of a perceived change in the dark areas of an image than in the light areas, there is a resultant change in perceived contrast.....Often, when working at a computer workstation, users turn off the room lights in order to make the CRT display appear of higher contrast. This produces a darker surround that should perceptually lower the contrast of the display. The predictions of Bartleson and Breneman are counter to everyday experience in this situation. The reason for this is that the room lights are usually introducing a significant amount of reflection off the face of the monitor and thus reducing the physical contrast of the displayed images. If the surround of the display can be illuminated without introducing reflection off the face of the display (e.g., by placing a light source behind the monitor that illuminates the surrounding area), the perceived contrast of the display will actually be higher than when it is viewed in a completely darkened room."

    Best regards and beautiful pictures,
    G. Alan Brown, President
    CinemaQuest, Inc.
    A Lion AV Consultants Affiliate

    "Advancing the art and science of electronic imaging"
     
  7. GeorgeAB

    GeorgeAB Second Unit

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    I was informed by one of my customers that he learned about bias lighting from this 30 minute video program:

    http://revision3.com/hdnation/koreatrip

    The portion discussing bias lighting is from 18:53 through 23:10. It doesn't mention my company or products but is the best presentation video I've seen on the topic to date. You don't have to watch the entire video stream. Placing your mouse cursor in the video image, once the video fully loads, reveals a slider you can use to select the right time into the program.
     
  8. Ed Moxley

    Ed Moxley Cinematographer

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    I guess rope lights would work good for bias lighting?
     
  9. GeorgeAB

    GeorgeAB Second Unit

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    I have tested many commonly available LED rope lights and have yet to find one that measures very close to 6500K (let alone the D65 video white point) even from companies who claim otherwise. None that I could find offers dimming. The conventional incandescent rope lights are quite yellow, and even more so when dimmed.
     
  10. JeremyR

    JeremyR Supporting Actor

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    I'm far from an ideal situation or a permanent setup for my home theater. I currently am in a cramped basement and sit about 6.5-7 feet away from my 30 day old wall-mounted 42-inch 1080P Panasonic Plasma tv. My wife won't let me use the big family room upstairs. But I've considered the options of putting some bias lighting behind the TV, because I feel my plasma is best viewed in a dark room and i would benefit from some bias lighting. My future Home Theater in my mind looks much closer to the picture on your website GeorgeAB. I don't intend to do a professional calibration of my television, but do plan on using DVE Blu-ray to try and get it as close as I can here shortly once I feel I've put enough hours on it that it has stabilized a bit. What would you recommend for lighting for somebody in my situation? It appears you do have a product or two in my range, but I know we probably can't get into too deep of a discussion on here about that probably.
     
  11. GeorgeAB

    GeorgeAB Second Unit

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    The Ideal-Lume Panelight model is designed specifically for your type of installation.
     
  12. JeremyR

    JeremyR Supporting Actor

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    I don't want it too bright. Would the two lights be too bright behind a 42 inch plasma? How would I mount them. Top and bottom, or on each side?
     
  13. GeorgeAB

    GeorgeAB Second Unit

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    Have you read the product description? The lights are adjustable for output. Most users mount them vertically behind the left and right ends of the panel, but top and bottom may work better for some installations. Some experimentation may be necessary to arrive at the most even illumination of the wall around the TV.
     
  14. GeorgeAB

    GeorgeAB Second Unit

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    Here's a direct link to just the bias lighting section of the video:
    http://revision3.com/hdnation/koreat...bias-lighting-
     
  15. Adam Gregorich

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    We added a bias light several years ago in our old media room. It made a big difference with eye fatigue. Before we added it after about two+ hours we would need to take a break. After adding it we could do a double or triple feature with no problem.
     
  16. GeorgeAB

    GeorgeAB Second Unit

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    http://static.hometheaterforum.com/imgrepo/b/bb/avatar-60-3.jpg[/img]][​IMG][/img] D65 BIAS LIGHTING: FUNDAMENTAL THEORY AND PRACTICE The technique of video bias lighting has been in use for decades by professionals and consumers who understand what is required for optimum picture quality and viewing comfort when using electronic displays. Video programs are mastered on calibrated professional monitors in "dim surround" conditions. It has long been understood that the best viewing condition for television programs is in a darkened environment. Total darkness is not recommended due to the limitations of the human visual system. Televisions and similar electronic displays are much brighter than large format front projection movie screens, which don't require supplemental illumination in the room. TVs are typically four to ten times as bright as the average commercial cinema! What are the recommended elements of properly implemented bias lighting? 1. The color of light should be as close as possible to the video white point of 'CIE D65' (loosely referred to as 6500 Kelvins) for color video viewing ['D50,' the 'E' point, or ~5400K in other specific applications]. 2. The color rendering index (CRI) is often published for a given lamp. A minimum CRI of 90 out of 100 is recommended for color reference applications. 3. The illumination should originate from behind the frontal plane of the screen to avoid reflections, haze, and glare (which interfere with, contaminate, and obscure the image). 4. The lamp itself should not be directly visible to the viewer, but rather the illumination should be reflected by surrounding surfaces or the wall behind the monitor. 5. The brightness of the reflected illumination should be 10% or less of the brightest white the monitor is adjusted to (calibrated for a dark environment). 6. Surrounding surfaces within the observer's field of view of the monitor screen should be neutral in color (gray to white), see: Munsell Color Order System's neutral value scale. 7. Completely surrounding the monitor screen with illumination is not necessary to realize the principle benefits of the technique. 8. It usually works best for the lamp to be mounted on the back of the monitor or TV cabinet (rather than on the wall), in order for the illumination to spread out over some distance. 9. Test patterns for adjusting bias lighting relative to the monitor screen are available in most optical disc programs for setting up home entertainment systems (see: 'Avia II- Guide to Home Theater,' 'Digital Video Essentials,' etc.). What are the proven benefits of bias lighting? 1. Reduces or eliminates eye strain and viewing fatigue in dark viewing conditions. 2. Eliminates image contamination due to reflections, haze and glare on the screen from conventional room lighting. 3. Enhances perceived black levels, contrast ratio, and picture detail by enabling dark adapted viewing. 4. Preserves correct color perception of the video image by the viewer. 5. Prolongs monitor phosphor life (phosphors are used in CRTs, plasmas, LCDs with CCF or white LED back lighting) by enabling dark room viewing and lowering of screen brightness requirements. 6. Provides a low level of illumination in the room for movement and peripheral activities.
    Says who? The following organizations are confirmed to define, recommend, specify, and/or use the technique of video bias lighting: The Society of Motion Picture and Television Engineers (SMPTE) The International Organization for Standardization (ISO) The International Telecommunications Union (ITU) The National Institute of Standards and Technology (NIST) The Metropolitan Museum of Art Industrial Light and Magic (ILM) The Imaging Science Foundation (ISF) THX, Ltd. Electronic Arts (EA) by deluxe Technicolor Microsoft Corporation Image Entertainment Universal Studios PostWorks Joe Kane Productions Ovation Multimedia DisplayMate Technologies CNET Labs Radical Games Factor5 Studios High Moon Studios CinRam Rev13 Films Advanced Television Evaluation Lab- Communications Research Centre- Canada Apple Corporation Filet Post Production Post and Beam Colorflow Post Cheyenne Mtn. Entertainment Zombie Studios CBS Television Twin Cities Public TV Deluxe Digital Studios Splice Here Slant Six Games New Hat LLC Roush Media Samsung Germany Digital Film Lab- Denmark Nice Shoes, VFX New York Desperate Housewives, Editorial Rockhopper Post Live Nation Studios LionAV Consultants Avical The Criterion Collection Max Post Bandito Brothers Studio Twin Cities Public TV Independent Edit Colorflow Post Headquarters Post Chainsaw Edit ABC Television The Moving Picture Company Technical references for more detailed explanations of bias lighting: SMPTE Recommended Practices document: RP166-1995: ‘Critical Viewing Conditions For Evaluation Of Color Television Pictures’ ITU-R BT.710-4 'Subjective Assessment Methods For Image Quality In High-Definition Television' ISO 17121:2000: 'Cinematography -- Work stations used for film and video production -- Requirements for visual and audio conditions' 'The Importance of Viewing Environment Conditions in a Reference Display System' G. Alan Brown, http://www.cinemaquestinc.com/ive.htm 'Digital Video Essentials: HD Basics' Blu-ray Disc program, by Joe Kane Productions 'Tips on Buying a New Flat Panel Display' NIST Flat Panel Display Laboratory, http://www.fpdl.nist.gov/Tips.pdf [includes graphic demonstrations of screen reflection issues] Pertinent technical quotes: "Monitor white reference: In additive mixture, the illumination of the reproduced image is generated entirely by the display device. In particular, reproduced white is determined by the characteristics of the display, and is not dependent on the environment in which the display is viewed. In a completely dark viewing environment, such as a cinema theater, this is desirable; a wide range of chromaticities is accepted as “white.” However, in an environment where the viewer’s field of view encompasses objects other than the display, the viewer’s notion of “white” is likely to be influenced or even dominated by what he or she perceives as “white” in the ambient. To avoid subjective mismatches, the chromaticity of white reproduced by the display and the chromaticity of white in the ambient should be reasonably close." from Charles A. Poynton, Digital Video and HDTV Algorithms and Interfaces Also see post #6 from earlier in this thread. Best regards and beautiful pictures, G. Alan Brown, President CinemaQuest, Inc. A Lion AV Consultants Affiliate "Advancing the art and science of electronic imaging"
     
  17. GeorgeAB

    GeorgeAB Second Unit

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    These videos demonstrate how even subtle changes in ambient lightness can instantly alter our black level perception of an object: http://www.youtube.com/watch?v=xl1lL...eature=channel ; ; http://www.youtube.com/watch?v=kdOQBPCOk5w&NR=1 . This explains why backing up a TV with a dark wall can be counterproductive in preserving convincing blacks on the screen. Only the darker portions of the screen image are enhanced by a lighter surround. The lighter areas of the image are not affected, therefore increasing perceived contrast ratio as well. These quotes document this characteristic:

    "Contrast could be considered to be the most significant quality that impacts not only the perceived depth of an image, but also affects the apparent sharpness.....While the luminance level of a given image affects how the eye perceives contrast and detail, the ambient conditions surrounding the image can also have a dramatic impact. This phenomena was studied by Bartleson and Breneman (1967) to examine the impact of perceived contrast based not only on the luminance level of the image but taking into account the surrounding ambient luminance levels as well. Their results showed that the perceived contrast increased as ambient luminance increased. With the increase in ambient luminance, the eye interprets black levels as being darker while the impact to the white level is minimal. Since the perceived difference in dark areas is greater under the higher ambient luminance conditions, the perceived contrast is higher. It is a natural tendency to want low ambient luminance levels to strive for "better" perceived image quality and what is thought to result in higher contrast. However, in reality, the opposite is true. This tendency may be justified for current direct view CRT televisions due to the issue of glare that results from the glossy surface of the glass tube [also true for certain flat panel displays today]. With less ambient luminance, the glare is reduced- but it may be important to keep some ambient luminance behind the television [as in the case of bias lighting] to keep the perceived contrast higher.....While sharpness can affect the apparent contrast of an image, the converse is true in that contrast can also impact the apparent sharpness of an image. Images that have lower contrast will appear to be not as sharp as an image of the same content, but with higher contrast.....A subjective study was then conducted to verify the impact that ambient lighting has on perceived contrast. Several non-technical (and thus presumably non-biased) and technical observers were asked to compare a series of images with various ALL [average luminance levels] under different ambient luminance extremes in order to understand the impact that ambient viewing conditions might have on the perceived contrast between the two television technologies [CRT and DMD (DLP RPTV)]. Under dark ambient conditions, the result for images with an ALL > 5% was found to be equal between the CRT and the first DMD display. However, under bright ambient conditions (about 250 nits of luminance on the wall behind all of the units), the DMD display was favored over the CRT by 50% of the observers as having higher perceived contrast.....This proved that ambient conditions have the effect of potentially raising the black level threshold of the eye above the actual black level of the television such that the perceived contrast ratio is higher." from the SMPTE Journal, 11/02. 'The Importance of Contrast and its Effect on Image Quality' by Segler, Pettitt and Kessel

    "Their experimental results, obtained through matching and scaling experiments, showed that the perceived contrast of images increased when the image surround was changed from dark to dim to light. This effect occurs because the dark surround of an image causes dark areas to appear lighter while having little effect on light areas (white areas still appear white despite changes in surround). Thus since there is more of a perceived change in the dark areas of an image than in the light areas, there is a resultant change in perceived contrast.....Often, when working at a computer workstation, users turn off the room lights in order to make the CRT display appear of higher contrast. This produces a darker surround that should perceptually lower the contrast of the display. The predictions of Bartleson and Breneman are counter to everyday experience in this situation. The reason for this is that the room lights are usually introducing a significant amount of reflection off the face of the monitor and thus reducing the physical contrast of the displayed images. If the surround of the display can be illuminated without introducing reflection off the face of the display (e.g., by placing a light source behind the monitor that illuminates the surrounding area), the perceived contrast of the display will actually be higher than when it is viewed in a completely darkened room." from 'Color Appearance Models,' by Mark D. Fairchild, Ph.D., of the Chester F. Carlson Center for Imaging Science: Munsell Color Science Laboratory

    Best regards and beautiful pictures,
    G. Alan Brown, President
    CinemaQuest, Inc.
    A Lion AV Consultants Affiliate

    "Advancing the art and science of electronic imaging"
     
  18. Adam Gregorich

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  19. GeorgeAB

    GeorgeAB Second Unit

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    Here are a couple of pertinent excerpts from Charles Poynton's 5/26/10 article titled: 'B, V and M Are Obsolete' "I use the word “reference” because the display used at the end of the content creation chain establishes the intended reference for all downstream displays. If an identical display is present downstream in an identical environment, then it should present an identical picture. In the consumers’ premises, we don’t expect the tight tolerances of a studio display, but we do seek the same aim points." "Color appearance is strongly influenced by surround conditions. My recent proposal for a new standard is entitled 'studio HD reference display and viewing conditions.'" [emphasis is mine]
     
  20. Adam Gregorich

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