HDR’s Background

Several years ago, a group of researchers from the University of British Columbia in Vancouver started BrightSide Technologies, working with HDR technologies and other display technologies.

Dolby acquired BrightSide in April 2007, keeping the research team intact and making it the Dolby Canada division of Dolby. Voltolina says Dolby had been working on HDR on its own for a few years, so adding BrightSide made sense.

“Dolby has been working on video internally for a long time,” he says. “We’re selling a digital cinema platform in the market already. . .We look at what other technologies can improve the entertainment experience, audio and video combined. Dolby is really committed to this area (video), with the same quality of commitment Dolby has had in audio.”

With its HDR displays, Dolby adds improved brightness to HDR’s true black capabilities to give users depth to images they won’t see on standard LCD TVs and computer displays.

“That creates an extreme contrast,” Voltolina says. “It’s very appealing to the eyes. It’s how we see contrast naturally. The picture just looks better, but it also translates into a better understanding of the image. The image is very, very realistic in terms of depth. If you have high contrast with depth, it’s very appealing.”

Dolby’s business model with HDR will consist of licensing the technology; the company will not manufacture the HDR displays itself.

Breaking Down Video

Before delving into the specifics of HDR, let’s consider some of the building blocks of video and displays.

LDR. Most video images today are LDR (Low Dynamic Range), even though very few companies use that term (because LDR video is so common). Today’s video consists of an 8-bit value (or 256 shades) of the three RGB channels (red, green, and blue). Combining those RGB channels yields 24-bit true color (about 16.7 million individual colors).

Luminosity. Measurements of brightness, called luminosity, appear in candelas per square meter (also called nits). LCDs and TVs produce about 300 to 600 nits.

Candelas measure the amount of light from a light source. A 100-watt light bulb emits about 120 candelas of light.

Contrast ratio. The idea of contrast ratio seems simple enough: It’s a measurement of the difference between the darkest and brightest capabilities of a display. A larger ratio indicates a display or TV that can achieve deeper blacks and brighter whites. LCD monitors and TVs typically have a contrast ratio of between 500:1 and 1,000:1.

To measure contrast ratios, manufacturers typically display the darkest possible spot in one area of the screen and the brightest possible spot in another area. A light meter then can measure the difference between the two spots, yielding a contrast ratio.

One drawback to relying on contrast ratios, however, is that no industry standard exists for determining and measuring the ratios. Manufacturers can tweak the methods for measuring the ratios to give their displays a more favorable contrast ratio rating. So you might find a display or TV that touts a great contrast ratio, but you might not receive those results in your living room.

Putting HDR To Work

With standard LCD screens, true black (and, consequently, a high contrast ratio) is difficult to attain because of the backlight used inside the screen. HDR fixes this problem and creates a much larger contrast ratio. The biggest difference between HDR LCDs and standard LCDs is the backlight. The CCFL (cold-cathode fluorescent lamp) bars in the standard LCD backlight become an array of LEDs in the Dolby HDR display backlight.

With its LEDs, an HDR LCD greatly improves on the specifications found with a standard LCD. For example, an HDR display can have a contrast ratio of 200,000:1 or more and a luminance of 3,000 nits or more.

Another improvement occurs in the amount of data the HDR display generates. By definition, HDR involves 16 bits of data per color channel, double what LDR provides. The additional 8 bits of data comes from the HDR display software’s adjustment of the brightness value of the individual LEDs (called the luminance channel). Because the brightness value of each LED has 256 possible individual settings, it requires 8 bits of data. The combined image data between the LEDs and LCD yields the 16 bits per color channel for the HDR display.

Even though the HDR display contains millions of pixels versus thousands of LEDs, the HDR software can change the luminance level of each LED faster than the video refresh rate, which allows individual LEDs to successfully control a group of pixels. (Because an LED is a solid-state device, the software can change each LED from “on” to “off” or any level in between in a few nanoseconds.) You can think of the LEDs as producing a low-resolution luminance pattern of the light, which then shines through and enhances the high-resolution LCD pattern of the image.

In addition, the software driving the display “peeks” ahead at the upcoming video frames, anticipating which LED brightness amounts need to be adjusted.

These factors give Dolby’s HDR its unique and superior capabilities. Other companies, including NEC, already have developed LCDs using LEDs for the backlight, but those screens don’t provide HDR capabilities.

At this point, HDR technology can display non-HDR content by stretching the luminance of that content to 16 bits, thereby creating “virtual HDR” content. Most cameras used to create movie-quality video already capture the data needed for HDR content, Voltolina says. However, because current display technologies cannot display HDR, the content providers simply discard the data needed for HDR.

“The data is useless because it can’t be displayed,” he says.

As HDR TVs begin appearing in the market, content providers should begin keeping the HDR data, meaning the creation of HDR-specific content won’t be overly difficult.

The Future Of HDR

Even with its acquisition of BrightSide, Dolby isn’t the only company researching HDR displays. Both Philips and Samsung have given HDR demonstrations at various tradeshows in the past couple of years. The Max Planck Institute in Germany, along with the University of Central Florida, also is researching HDRs.

Although HDR technology would work on any size TV, Voltolina expects companies to only offer HDR TVs at sizes of 32 inches and larger.

“With a smaller screen size, people probably won’t pay extra for the quality,” he says. “There is a segment of the market that is cost-driven, and that’s their choice. But this feature (HDR) differs greatly from the differences you’ll see from 1080i to 720p, where the difference is nowhere near as obvious (as standard LCD to HDR LCD).”

Voltolina says Dolby isn’t ready to release an exact cost estimate for HDR LCD TVs, although they will cost more than similarly sized standard LCD TVs. During the next couple of years, the costs for manufacturing LEDs should continue to drop, which should make HDR displays more competitively priced.

Voltolina says manufacturers could offer HDR displays in three price ranges for each size of display, because HDR display technology allows the manufacturer to control the display quality by adjusting the number of LEDs included in the backlight. The most expensive HDR displays will have the most LEDs; midrange and low-range displays will use fewer LEDs.

In the world of LCD TVs, adding a new feature that truly makes a difference hasn’t been easy. Most LCD TVs look the same, regardless of the company’s name on the console.

“Manufacturers are so eager to differentiate their product,” he says. “The LCD TV manufacturers are so consolidated in the supply chain. Now, they only can really differentiate their products on price point. They’re eager to differentiate on the picture.

“In general, I have not heard anyone in the industry say that this technology won’t make it,” Voltolina says. “Instead, they say, ‘I want to have it first.’”

Of course, that’s after they’ve seen it to believe it.

by Kyle Schurman

Backlight Options LCDs make use of a backlight to illuminate the screen. The difference in backlights is one of the differences between a standard LCD and Dolby’s HDR (High Dynamic Range) LCD technology. CCFL. The backlights in a standard LCD are narrow fluorescent lights that typically stretch along the edges of the screen. Most LCD notebook screens, for example, have lights along one or both vertical edges. The light, a CCFL (cold-cathode fluorescent lamp), contains a mercury vapor that, when ionized, produces an ultraviolet light. The ultraviolet rays strike phosphors that coat the interior of the glass tube, and the phosphors produce a bright white light. A diffuser between the CCFL and the display screen diffuses and spreads the light evenly across the screen, providing the backlight for the display. The traditional LCD cannot vary the brightness of the CCFL tube. The CCFL tube needed for a typical laptop screen is about half the diameter of a pencil and slightly longer (as shown at right). A circuit board inside the LCD drives the CCFL. In the cutaway of a standard LCD screen shown on page 47, the CCFL is on the left side. HDR. With the HDR display technology from Dolby, thousands of LEDs make up the backlight for the LCD. (The LEDs can be all white or all tri-color.) An HDR manufacturer can vary the number of LEDs in the backlight; more LEDs would increase the cost of the screen but would provide greater quality. The display software analyzes the video image dozens of times per second, determining (and adjusting accordingly) the proper brightness for each LED in the array. True black. When black is required in a part of the HDR display, the software turns off the backlight LEDs in the area, which gives the LCD screen a true black. The LEDs can range in luminance from 0.015 nits to 3,000 or more nits. This wide range of luminance results in an HDR display with far more depth and contrast than a standard LCD. With a standard LCD screen, the CCFL is always on, meaning, when trying to create black, the LCD screen must try to block as much light from the CCFL backlight as possible. However, some light from the CCFL backlight always will bleed into the area where black is required, leaving it well short of true black. "You have to stop as much light as possible," Dolby’s Voltolina says. "That's not very practical.” Beyond the overall quality of the light, using LEDs instead of CCFLs in the backlight offers two significant benefits. First, there is no mercury in LEDs (unlike CCFLs), which helps environmental concerns. Second, Voltolina says, LEDs can provide a 35 to 40% energy savings versus CCFLs when creating the same amount of light. Source: Dolby (and BrightSide Technologies)

HDR Specifications Front view Dolby is using the DR37-P TV (that BrightSide Technologies initially developed) as a prototype to demonstrate HDR's capabilities. Dolby's business model for HDR is such that the company will not make the HDR displays itself, but it will license the technology to LCD manufacturers. Even though Dolby hasn’t released the specific dimensions of this prototype, you can see from these examples of the DR37-P, the console size of an LCD TV with HDR capabilities looks identical to a standard LCD TV, including a thin console. Side view Specifications for the 37-inch DR37-P screen include: • Highest luminance (white): More than 3,000 nits • Lowest luminance (black): 0.015 nits • Contrast ratio: More than 200,000:1 • Color channel: 16 bits per color • Resolution: 1,920 x 1,080 HD • Number of LEDs: 1,380 Source: Dolby (and BrightSide Technologies)

HDR In Action The HDR software can control the brightness value of each individual LED, using one of 256 different brightness levels (as shown below). When trying to create a true black, the LEDs in that area are turned off. LED pattern Actual image As shown at right, the HDR software gives the LEDs in the area of the brightest portions of the image the highest brightness levels. LEDs in areas of the image that are darker receive lower brightness levels. Notice how brightness of the LEDs (upper right) match the brightest and whitest areas of the image (lower right). (Each square in the upper-right image represents an individual LED.) In areas of the white sails that have a slight shadow on them, the LEDs are not as bright as in areas of the sails with no shadows. In the darkest areas of the final image (the hull of the boat and the sky with no clouds), the LEDs are turned off. Source: Dolby (and BrightSide Technologies)