By Tom Coughlin
Indian Wells, California — At the 2014 Hollywood Post Alliance Retreat (http://hollywoodpostalliance.org), the session on “Better Pixels: Best Bang for the Buck” gave some interesting insights on how we can make better displays — displays made for humans. Participants on the panel pointed out research as well as subjective experiences with 4K as well as HD TVs show that 4K by itself doesn’t lead to a better visual experience.
The session participants said that higher resolution isn’t enough and that in addition to more pixels we also need faster pixels (higher frame rates) and better pixels (better contrast and extended luminance levels). If we really want to make a better display it must reach beyond the limitations of prior display technology.
In Figure 1, from Pat Griffis’ (Dolby) talk, we can see that the human eye has a total sensitivity to light from 1 millionth candelas per square meter (nits) to close to 100 million nits. The low end of this range requires complete adjustment of the eye to a dark environment and the upper range can hurt the eye (e.g. looking at the sun). Pat said that a realistic range for human visual perception is 0.005 to 20,000 nits (satisfies 90% of viewers) in terms of what they can see with out strain or pain.
As shown in Figure 2, Blu-ray content after passing through all the process filters only delivers a full dynamic range of 0.117 to 100 nits.
Robin Atkins created a volumetric model of human perception that is much expanded from the traditional 2D color gamut models. He called this model a color volume, the palette of all available colors at all available intensities. Examining the visual threshold vs. intensity he showed that an acceptable trade off seemed possible with a 10k nit peak volumetric container, XYZ color primaries and a-12 bit perceptual quantizer.
Matt Cowan from Entertainment Technology, Canada, referred us to a SMPTE Motion Imaging Journal article by Andrew B. Watson from NASA Ames Research (SMPTE Mot. Imag. J, 2013, 122:18-22). That analyzes judder and flicker and how motion and brightness are related. This presentation explored how to determine the occurrence of alias events and their relationship to visual frequencies. Masayuki Sugawara from NHK labs discussed tone reproduction and high dynamic range.
The session made it clear that we can create a better human display experience by not just focusing on the number of pixels in an image but also improving the luminance dynamic range as well as the proper values for image frequency. The challenge in making a display made for human that can be purchased by humans is to do this with low costs. With future increases in processing power, bandwidth and storage capacity we should be able to make such a display possible.
Tom Coughlin, the founder of Coughlin Associates (www.tomcoughlin.com) has over 30 years of magnetic recording engineering and engineering management experience at companies developing flexible tapes and floppy disc storage as well as rigid disks at such companies as Polaroid, Seagate Technology, Maxtor, Micropolis, Nashua Computer Products, Ampex and SyQuest. He can be reached at firstname.lastname@example.org.