Video Displays: How Good Is Good Enough? Pt. 2
The Avatar sequel is reportedly being shot at 120 frames per second—5 times the
frame rate of the traditional 24 fps.
In Pt. 1, I discussed how improvements in color space and dynamic range are bringing video displays closer to the abilities of the human eye. Here I’m going to discuss the impact of spatial resolution and refresh or frame rate.
Pixels get all the attention when most people pick out their TVs. 2K, 4K, 8K—how many K’s do I need? But just because a display can put more pixels on the screen doesn’t mean they’re better pixels.
Everyone has had the experience of going to the eye doctor and straining to see if that E is pointing up or down, or left or right. As you go from the top line to the bottom, there’s a point where you can no longer determine which direction the E is pointing. This is how the eye doctor determines your sensitivity to spatial resolution.
My eyes aren’t quite as good as they used to be, but on a flat-screen TV, I can see pixels on a 1080 display when I’m standing about 3X the picture height back. On a 4K, I can’t see pixels until I get inside of 1.5X the screen height. With projectors, you need to be even closer to see pixels as a result of the natural smoothing affect of convergence and optical lenses.
If I’m staring at a spreadsheet, those pixels and distances are pretty accurate, much like staring at those E’s at the eye doctor. But if I’m watching a movie, I’m not straining my eyes to see pixels but instead want to take in the whole image, so I’m moving further back. 4K allows me to sit comfortably about 2X the screen height back, which is as close as I’d ever want to watch a movie. So for the future, don’t give me more pixels, give me better pixels!!!
So far, I’ve been talking about pixels, but unless I’m only talking about spreadsheets, I need to understand more about how the human eye sees motion. After all, I want to watch movies!
James Cameron, of Avatar fame, was one of the first Hollywood producers to push HFR (high frame rate). The original movie spec was 24P, and it was chosen because it was the lowest refresh to allow acceptable audio quality. This means that the entire image on the screen is refreshed 24 times per second.
If I’m watching two people sitting across a table from each other talking, slow frame rate doesn’t bother me. But if I’m watching a plane fly across the sky, or Matt Damon jumping from one building to another in a chase scene, I need faster refresh rates. When you look in the sky and see a plane fly by, you see it move in a nice, smooth continuous motion. But when you watch a movie in 24P, the plane will seem to jump across the screen as it moves from frame to frame. Your brain naturally tries to smooth this out, but when you watch two scenes—one with HFR and one without—you appreciate the difference.
The critics say HFR makes images seem “soap opera”-like, but honestly, isn’t that the way we see things in real life? When we walk through everyday life, does the world look more like a soap opera or a movie? (I did say “look” and not “feel.”)
So currently we hover between 24P for movies, and 60P for video. Experts seem to feel that the threshold for the human eye is around 120Hz (which is what the Avatar sequel is rumored to be shot in). Let me please note that HFR means the movie or content was shot or captured in this high frame rate, not just displayed at faster refresh.
Many flat panels tout 240Hz or even 600Hz refresh, but that is just refreshing the same content on the panel and is intended to fix deficiencies in the panels, not in the quality of the movie. HFR requires a lot of bandwidth, so improvements here are costly, but they have a big impact on the way we see images. So expect this to take a little longer than the other items discussed here.
In the past 10 years, we’ve seen improvements in all aspects of display performance that affect visual acuity. In the next 10 years, we will see even more improvements. The most important thing is that it’s not just about resolution. Getting to 8K will not bring us to the ultimate display. In fact, most people won’t see any improvement from going from 8 million pixels to 33 million pixels. If we all want to watch video and have it replicate real life, we don’t really need more pixels—we need better pixels. Give me pixels with more color, more contrast, and refresh them on the screen faster. In the meantime, give me content that will really take advantage of all that my current 4K UHD display can handle.
A 25-year veteran of the video-display industry, George Walter has been a vice president
at Digital Projection, where he founded its residential division, and a board member for both
CEDIA and Azione. George is the President of Rayva.