Scott,
Thanks for arranging this interview with Joel. I must say, you are one energetic fellow! It seems every time I turn around you are producing more helpful and interesting material for us videophile/audiophile types. Perhaps we can get together again at CEDIA EXPO in Denver this September. I expect you will be roaming around the show floor interviewing more people. You have to stop and eat at some point, though.
One of the aspects of this interview I enjoyed the most was Joel's focus on human perception. I see often that discussions of gamma/EOTF in the forum fail to mention the connection with ambient light level and how humans perceive video images in varying lighting conditions. Video is based upon human visual perception, not the other way around. Many facets of how video should be implemented in an entertainment system are confusing for folks without a fundamental understanding of human factors. I first learned this from Joe Kane, Joel Silver, and their work in the Imaging Science Foundation back in the mid to late '90s. Anyone wanting to design a video reproduction system correctly must understand such fundamental principles. The ISF's original mission included a major focus on training their students how to design good systems, not just calibrate displays.
One thing Joel and I differ a bit on is the suitability of bias lighting behind larger displays. Even the International Telecommunications Union (ITU) recommends bias lighting usage with HD images occupying a 30 degree viewing angle, at only 100 nits screen brightness. The 30 degree viewing angle addresses optimum image size for 1920 x 1080 pictures. Actual display dimensions have no meaning without determining what the seating distance is. This is specified in ITU-R BT.710-4 'Subjective Assessment Methods For Image Quality In High-Definition Television'. As Joel pointed out, this is a recommendation, rather than a formal standard, which allows for differing opinions. There are differences between specific humans, of course, when it comes to their sensitivity to eye strain and viewing fatigue. However, standards bodies such as the ITU, SMPTE, EBU, etc., offer general recommendations that they have determined will apply to the majority of technology users.
There is another factor that needs to be considered in evaluating the impact of brighter, and high dynamic range (HDR), displays regarding viewing fatigue. Joel mentioned how the eyes can occasionally shift focus upon a dark perimeter around a 42" TV, while viewing a video program in a darkened room. He compared this to having a flashlight pointed into your eyes in the dark. This sudden, dramatic, shift in light level strains the eyes- causing us to typically flinch, squint, and/or blink. Our eyes are adaptive, but only up to a point. This sudden and dramatic change also occurs in actual video programs as well.
This characteristic of typical video program viewing can be demonstrated very easily. Any viewer can turn all the lights out at night when viewing a program, then turn to face away from the TV for a few minutes. It is common to see the room lit up by the screen, then strobe and throb as the light varies from scene changes. This is a technique used by program authors to keep the audience's attention. It stimulates the typical viewer's interest to alter the scene composition frequently through the use of varying camera angles, change of objects or people in the frame, varying light levels, etc. I have found that a greater factor in eye strain has to do with changes in image brightness more than image size.
Keep these interviews coming. It's so rare that average forum members get such exposure to world class authorities, experts, professionals, innovators, and practitioners.
Best regards and beautiful pictures,
G. Alan Brown, President
CinemaQuest, Inc.
A Lion AV Consultants affiliate
"Advancing the art and science of electronic imaging"