HDR displays are the next step toward true-to-life visuals

6 févr. 2017

Qualcomm products mentioned within this post are offered by Qualcomm Technologies, Inc. and/or its subsidiaries.

The progression toward true-to-life visuals has been on a rapid pace for many years. Although much of the focus has been on increasing pixel resolution and supporting faster refresh rates to achieve a more immersive experience, pixel quality improvements are also paying massive dividends. If you attended CES 2017, you know it was difficult to go anywhere on the show floor and not be awestruck vibrant screens with fantastic color, brightness, and contrast. The common theme was High Dynamic Range (HDR). To be clear, we are not talking about HDR capture, which most consumers are aware of as a camera feature. We are talking about a change in the content and, importantly, both the processing and display panels that allow for HDR visuals on our screens. So what’s the big deal about HDR?

HDR images and videos are visually stunning since they are much more realistic and immersive. HDR gives us the brightest brights and darkest darks. It allows us to see details in the shadows and not have the whole image washed out by one bright object. It gives us smooth color transitions rather than color banding. HDR simply offers us a closer representation of how the real world looks.

In the image above, you can see how the “HDR OFF” side (in comparison with “HDR ON”) fails to show the detail in the shadows (the rock wall close to the water) and provides less vibrant colors (the rock wall and the water). Three technology vectors are essential for HDR to increase visual quality and make sure that every pixel counts.

  • Contrast and brightness means that you get brighter whites and darker blacks closer to the brightness of real life.
  • Color gamut can be thought of as the range of colors. It is a subset of visible colors that can be accurately captured and reproduced by either graphics, photography, or displays.
  • Color depth is the number of gradations in color that can be captured and displayed. It is associated with the bits per pixel.

Achieving realistic HDR is challenging since real-life brightness has a wide dynamic range that is hard to capture and replicate. For example, the luminance of the sun is approximately 1 billion nits (a measure of brightness), while the luminance of starlight is around 0.001 nits. This huge variation means that the dynamic range of light in the real world is approximately 10^12 to 1 (or 1 trillion to 1).

For our devices, the camera attempts to capture the real-world light, and the display attempts to replicate it—but they both fall short. Camera sensors typically have a dynamic range of less than 1000 to 1 for a single still image capture. Modern LCD displays used in smartphones typically support luminance values only in the range of 500 to 0.1 nits. Human vision, on the other hand, is quite large and can accommodate a dynamic range of approximately 10,000 to 1 in a single view and 1,000,000 to 1 in a dynamic view. In other words, our eyes can see the difference.

It’s not just brightness. Our devices can’t capture and replicate all the colors in the real world. Devices and video systems up to now have been based on the BT.709 and BT.601 color spaces, which contain only a small percentage (about 33.5%) of all visible colors.

HDR10 is the next step toward true-to-life visuals. The HDR10 specification has a variety of requirements, specifying minimum requirements for the actual content and the visual processing. ULTRA HD PREMIUM, which is the brand name consumers will most likely encounter when shopping for a device, requires HDR10 and in addition sets requirements for the actual display.

HDR10 requires visual processing enhancements to the three essential technology vectors of HDR:

  • Contrast and brightness: HDR10 supports a new electro optical transfer function (EOTF) that expands the maximum brightness from 100 nits to 10,000 nits.
  • Color gamut: HDR10 supports a wider color gamut defined by BT.2020. BT.2020 represents 57.3% of the visible color spectrum as opposed to the 33.5% covered by the previous standards, BT.709 and BT.601.
  • Color depth: HDR10 supports 10 bits per color channel (red, green, and blue) for a total of 30 bits per pixel, which means the ability to represent over a billion colors. Compared to 8-bit color channels of the previous standard, HDR10 offers up to 64x more colors, which is most useful for smooth color transitions to remove banding.

As a side note, HDR10 also requires support of HEVC Main 10 video decode.

So why are we talking about HDR10? The technologies and ecosystem are aligning to make HDR10 possible. In terms of key ecosystem drivers, devices such as TVs, and content such as movies and TV shows from Netflix and Amazon, are already available. On the technology side, we’ve seen exponential improvements in many technologies to make HDR10 possible, such as multimedia technologies (graphics, video, image, and display processing), displays (increased pixel density, viewing angles, and color gamut), and power efficiency.

Qualcomm Technologies is playing a large role in making HDR10 possible. The Qualcomm Snapdragon 835 processor supports HDR10 video decoding all the way out to the display for richer, truer colors — in other words we are ULTRA HD PREMIUM ready. To efficiently enable HDR10 within the constraints of mobile devices, Snapdragon 835 takes a heterogeneous computing approach.

Heterogeneous computing utilizes specialized engines across the SoC for efficient processing, providing high performance at low power and thermals. On Snapdragon 835, just about the entire SoC is used to execute the various HDR tasks, such as the Qualcomm Adreno 540 GPU for graphics processing, the Video Processing Unit for HEVC Main 10 video profile support with metadata processing, and the Display Processing Unit for both color processing (tone and gamut mapping) and native 10-bit color BT.2020 support over HDMI, DisplayPort, & DSI displays.

We’re excited about HDR10 since it will enhance the visual quality on all the screens in our lives, from smartphones and tablets to VR headsets and TVs. HDR10 will bring us one step closer to our ultimate goal: visuals so vibrant that they are eventually indistinguishable from the real world.

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Qualcomm Snapdragon and Qualcomm Adreno are products of Qualcomm Technologies, Inc.