Video Displays: How Good is Good Enough?
The last few years, we’ve seen continual improvement in the performance of flat-panel TVs and projectors. Where will it stop? What is the Holy Grail in video display anyway?
The answer to that question is different for everyone, but the solution is the same. When the display is capable of creating an image that meets all the limitations of the human eye, there’s no reason to keep improving. Everyone’s eyes see the world slightly different, whether it be color, contrast, sharpness, or action. That’s why some people hate 3D and others love it. (But that’s a topic for another discussion.)
To compare what a typical person can see versus today’s top displays, we need to look at four areas that affect the imaging in the human brain: color, contrast, spatial resolution, and refresh or frame rate.
First, let’s look at color. We’ve recently heard talk about “color space” or “color gamut.” This is defined in fancy three-dimensional charts, but basically it’s the total volume of color the eye can see or a display can create.
When REC 709—the color standard for HDTV—first came out, it could reproduce about 35% of the total colors the human eye can see. P3, or digital-cinema color space, took the amount to about 50%. Most of us—especially those of us who remember NTSC—think this looks incredible, and yet we’re still only at 50%.
The triangle within the chromaticity diagram on the left shows the color space for HDTV while
the triangle on the right shows the significantly expanded color space for 4K Ultra High Definition
New discussions are about REC 2020, which will take the total color space to 75% of what the eye can see. Some flat panels can do this now, but projectors have a tough time reaching this with conventional lamps and will require pure RGB laser to achieve both the color space and light output needed to really appreciate all those colors.
In roughly 10 years, we’ve doubled the color space that can be seen on a consumer display, yet very little content is available to appreciate the full scope of this improvement. There’s still some room for improvement, but the big gains have already been accomplished.
Now let’s look at contrast. The human eye is an amazing organ. If you remember from science class, it’s made up of cones and rods, which are microscopic sensors that can detect content and send images to the brain.
Rods work at very low light levels (like when you wake up in the middle of the night) and cones need a lot more light and are used to see color. At night, the iris in our eye opens up to let more light in, but the rods don’t detect much color so we pretty much see in black and white. In this condition, we can see a lot of detail in black levels. On a nice sunny day, we get lots of light and color into our eye, and the cones take over. If we compare what the human eye can see in low light levels to what we can see in bright daylight, our range of contrast is huge.
HDR (high dynamic range) comes much closer to approximating human vision than
does SDR (standard dynamic range)
This is the magic of HDR. By applying different values to bright scenes than it does to dark ones, it more closely matches how the human eye responds, providing much more dynamic contrast. HDR has the most overall impact on picture performance than anything we’ve seen since HDTV, and yet few can explain how and why it works. (Not to mention that there are so many watered-down variations.) But let your eye decide, and it will see the impact of HDR every time from anywhere in the room.
In Part 2, I’ll talk about spatial resolution, refresh or frame rate, and why pixel counts aren’t as important as you might think they are.
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.