When we watch a video, it’s easy to assume that the things that appear in that video—cars, people, plants, and so on—look just like the objects that the filmmaker recorded. If the car in the video is royal blue, for instance, we assume that the car the filmmaker shot was that same shade of royal blue.
But it’s usually not that simple. If you’re watching a television show or a movie, it’s likely that a great deal of care went into the way the colors of each and every scene appear.
Dolby’s Shane Ruggieri is a professional colorist who has spent years working with colors in film and video to help tell stories. Sometimes he changes the color palette of a scene for emotional reasons: heightening the red to communicate anger, for instance, or adding a sickly yellow-green to hint at horror.
Other times the changes Ruggieri makes are practical: by lowering the average brightness and shifting colors toward blue, he can make a scene shot in daylight look like it takes place at night.
But one of the tasks colorists hate is having to compromise a scene’s colors just to fit into the limitations of today’s TVs. The gamut, or range, of colors that current TV standards support is quite limited—not only is it far less than the colors the eye can see; it’s also far less than the colors that today’s cameras can capture.
Ruggieri likens it to being asked to write a story, but not being allowed to use 10 letters of the alphabet. He says it’s like telling the filmmaker: “Go tell a story based in reality, but you can’t use all of the reality you see.”
Why is the color gamut of TVs so limited? It’s related to the lack of brightness and contrast available in today’s TV technology, something Dolby’s Mike Rockwell wrote about in “Is your TV bright enough?”
In the real world, there’s a vast spectrum of brightness. The cheerful yellow of a flower in sunlight can be as bright as 14,700 nits, for instance. (Nits are a measure of brightness, also known as candelas per square meter, or cd/m2. For reference, a 100-watt lightbulb radiates about 18,000 nits.) The hood of a silver car may put out 6,000 nits. Even a patch of black asphalt can put out 2,100 nits on sunny afternoon.
All this makes it surprising that today’s TV standards top out at only about 100 nits—only a fraction as bright as that patch of black asphalt.
The brightness deficit of today’s TV standards has a direct effect on the colors you see in broadcast television.
Here’s how it works: white is the brightest color in any display, since it is made up of all the other available colors. If the brightest your TV image gets is 100 nits, that means every color that isn’t white must be less than 100 nits. Suddenly, that sunny yellow of the flower—14,700 nits when it was filmed—becomes a dull, muddy 80 nits when represented on your flat screen at home. The green of a California highway sign or the red of a London bus? They’re just too bright to be properly represented on your TV at all, requiring colorists to substitute different colors they hope look right, relative to the rest of the scene.
“Reality is a lot different than what you can show on a TV,” Ruggieri said. “That’s the big challenge—how to get a viewer to relate deeply to a scene or story when you can’t show what the director sees on set or even what’s captured by the camera.”
Contrast is key
The story isn’t just about brightness, though, it’s also about contrast. Displays that have greater contrast can show more subtle gradations between shades of color. And those subtle gradations—effectively a larger number of available colors—in turn reinforce the overall sense of contrast. Improving contrast, along with adding technical innovations like higher bit-rate image data, lead to a more realistic image than was previously possible.
If you can see subtle shifts between different shades of yellow in a flower, for instance, it helps you detect the depth and detail of the image. The scene becomes less like a video and more like real life.
At Dolby, our goal has always been to give the creative community the tools they need to express their artistic vision with as few technical limitations as possible. We’re now focused on overcoming the limitations on brightness, contrast, and color gamut that today’s TV standards impose. We won’t be manufacturing TVs ourselves, but we’ll work with our top-notch partners who do.