By Mike Rockwell, Executive Vice President, Advanced Technology Group, Dolby Laboratories
When most people think about Dolby, they think about high-quality sound. But those of us who work at Dolby know that our mission is about high-quality entertainment and communication. That involves sound and images. Lately, we’ve been thinking a lot about the image part of the puzzle, and we’d like to share some of that thinking with you.
All our efforts at Dolby start with an understanding of the science of human perception. With imaging, we start with human vision. And let’s state one thing at the outset: Human vision is an amazing thing.
You probably remember some of the details from a long-ago biology class: Your eye is filled with millions of rods and cones, both of which detect light and send signals through the optic nerve to your brain. Roughly 30 percent of the brain is dedicated to interpreting those signals and turning them into our visual perceptions.
When we look at the world, we think of objects and colors. But vision is really about light. Our eyes don’t detect a car; they detect the light bouncing off a car. The reason the car is blue? It reflects light in the blue wavelength and absorbs light in other wavelengths.
Our eyes can adapt to hugely varying intensities of light exceptionally smoothly. We can walk from a bright sunny day outside into a gloomy, dark house, and within seconds our eyes adjust.
But that doesn’t mean that we can see equally well in any light situation. Wake up early in the morning in your darkened bedroom. You can see shapes of objects on the floor, but not their colors. Under a single dim lightbulb in your closet, it may be difficult to distinguish a green sweater from a brown one. Take them outside on a sunny day, though, and you can see not only subtle differences in color but details in the texture.
But as we all know, there’s an upper limit. If the day gets too bright, everything is washed out in a sea of glare.
The super TV
At Dolby, we wanted to find out what the right amount of light was for a display like a television. So we built a super-expensive, super-powerful, liquid-cooled TV that could display incredibly bright images. We brought people in to see our super TV and asked them how bright they liked it.
Here’s what we found: 90 percent of the viewers in our study preferred a TV that went as bright as 20,000 nits. (A nit is a measure of brightness. For reference, a 100-watt incandescent lightbulb puts out about 18,000 nits.)
You may be thinking, “Wow, I don’t want to look at a TV that bright. Looking at a 100-watt bulb would hurt my eyes!” And you’d be right if the TV was displaying a full-screen, pure-white image. That would be uncomfortable.
But real TV images, like scenes in the real world, include a mixture of dark and light. Only small parts of real-world scenes are very bright, and we have no problem looking at them. In fact, one of the secrets to producing TV images that look like real life is having that mix of true brights and darks.
If viewers want images of as much 20,000 nits, guess what the industry standard is for the brightness of current TV images. (Go ahead, we’ll wait.)
If your guess is more than 100 nits, you’re wrong. It’s true—most viewers want TV images that are 200 times brighter than today’s industry standard.
Does that difference really matter? You bet it does. Today’s TVs simply can’t match the depth and detail of a display that can produce far brighter images. And conventional TVs can’t recreate all the colors found in the world around us. It’s a classic case of “you don’t know what you’re missing until you see it.” When you experience a display with much higher brightness, you never want to go back to a conventional display.
The role of contrast
But brightness is only part of the story. Contrast—the difference between light and dark areas of the picture—also plays a very important role. Your eyes have an incredible ability to perceive contrast. Even if the whitest white on the part of the screen you’re viewing is as much as 10,000 times brighter than the darkest area (a difference known as the contrast ratio), most people will still be able to perceive both parts of the image without a problem.
But that doesn’t mean that a 10,000:1 contrast ratio is all a display needs. As I said above, your eye adapts as it moves from brighter to darker areas. And that adaptation happens even as your eye is roaming around an image. That means that you can see a 10,000:1 contrast ratio in a bright area of the image, then look at a different part of the same image and see a 10,000:1 ratio in a dark area. When you combine all those ratios, you find that a high-quality display should be capable of a contrast ratio of 100,000:1 or more.
If you just raise the brightness of a TV display without increasing the contrast, you end up with dull, washed-out images. When you raise both, something magical happens: images on the TV start to look like the real world. It truly seems like you are looking out a window and not at a display. Exciting.
What are we doing here at Dolby with what we’ve learned about light and displays? We’re developing a technology called Dolby Vision that we’re convinced will revolutionize television. We’ll have more details soon, so—as they say on TV—stay tuned.