What is HDR?

Posted Fri Apr 28, 2017 at 06:15 PM PDT by
HDR sample

Keeping track of the latest audio and video tech can be daunting. Thankfully, High-Def Digest has you covered. Welcome to our new Home Theater 101 series, where we'll be explaining emerging technologies while also recommending the very best possible A/V gadgets n' gear you can buy at your particular budget level. 

And when it comes to recent display advancements, few are as buzzworthy as HIGH DYNAMIC RANGE.

But just what exactly is HDR and how does it work? And what's the deal with all of the competing formats? Fret not! If you don't know the difference between HDR10 and Dolby Vision, this guide is here to breakdown the ins and outs of High Dynamic Range. So, without further ado, let's dive right into...

HOME THEATER 101
WHAT IS HDR?

THE BASICS


High Dynamic Range, or HDR for short, is an advanced display and image mastering technology used on select 4K TVs and Ultra HD content. The process uses expanded brightness to improve contrast between dark and light aspects of an image, bringing out deeper black levels and more realistic details in specular highlights -- like the sun reflecting off of an ocean -- in specially graded HDR material.

This increased brightness performance is measured in nits. In general terms, the more nits a display can produce, the brighter the image and greater the HDR performance will be. The UHD Alliance currently requires LCD displays to produce more than 1000 nits peak brightness and less than 0.05 nits black level, or OLED displays to produce more than 540 nits peak brightness and less than 0.0005 nits black level to receive Ultra HD Premium Certification, ensuring an optimal HDR experience. With that said, there are still many displays that offer some level of HDR performance without reaching those numbers.

In addition to enhanced contrast, HDR is often also bundled with support for a Wide Color Gamut (WCG), offering a greater range of colors than those found in traditional HD sources and TVs using the previous Rec. 709 standard. This means that WCG content and displays can now produce more realistic colors, providing a more true-to-life representation of an image. Though current Ultra HD and HDR specs provide support for the Rec. 2020 wide color gamut, wider color gamut content available now is typically produced in the DCI-P3 color space (aka the color space where commercial cinemas operate).

Check out the chart below to see the differences between each gamut. The entire curve represents the full visible color spectrum. The smallest triangle represents the old Rec. 709 gamut; the solid triangle represents the wider DCI-P3 gamut; and the large dotted triangle represents the Rec. 2020 gamut. (Source: AVS Forum)

As you can see, the Rec. 709 gamut is missing out on many of the colors covered by the larger DCI-P3 and Rec. 2020 color spaces, allowing the wider gamuts to produce hues that don't even exist in the previous standard. 

When content is graded in HDR with WCG, the video is usually encoded with metadata. This metadata is then interpreted by an HDR display during playback, telling the TV what colors to render and how bright the HDR highlights should appear. HDR metadata is typically implemented in one of two ways: static or dynamic.

Static metadata uses the same HDR-grading for the entire video, offering one expanded range for the full runtime. In practice, this type of metadata leads to some dim scenes looking darker than they were originally intended. Meanwhile, dynamic metadata is able to adjust brightness levels on a scene-by-scene or even frame-by-frame basis, offering a more accurate HDR experience.

There are currently several different competing and co-existing HDR formats, with the two main options being: HDR10 and Dolby Vision, offering a variety of specific performance quirks, advantages, and disadvantages.

HDR10


The default HDR standard for most content, including Ultra HD Blu-ray discs, is HDR10, an open standard High Dynamic Range content and playback solution. The format supports the Rec. 2020 color space, a bit depth of 10-bits, and a max output of 1,000 nits. Likewise, HDR10 uses static metadata, but an expanded version of the format with dynamic metadata support, dubbed HDR10+, is being finalized. 

HDR10 playback is supported through the widest variety of displays on the market from manufacturers like Sony, Samsung, LG, VIZIO, and Hisense. HDR10 is also the required base HDR format for Ultra HD Blu-ray discs. Likewise, HDR10 content is available through several streaming services like Netflix and Amazon Prime Video, offering a growing collection of titles.

In order to watch HDR10 content, users will need an HDR10 capable display along with an Ultra HD Blu-ray player or HDR capable set-top box. Likewise, the format requires an HDMI 2.0a connection for external sources and HDCP 2.2 compliancy for copyrighted material.

HDR10+ is currently supported by all of Samsung's 2017 UHD TVs, including its premium QLED TV lineup. Likewise, the first HDR10+ content is set to launch through Prime Video later this year. Exact requirements for HDR10+ playback have not been confirmed yet.

DOLBY VISION


Serving as the main competitor to HDR10, Dolby Vision is a proprietary end-to-end HDR format that covers content creation and playback. Versions of the format are available in cinemas and home theaters, with the theatrical implementation being an integral part of the Dolby Cinema process, which uses the Dolby Vision laser projection system. Currently, there are more than 50 Dolby Cinema locations around the globe (HERE is a list of Dolby Cinema at AMC locations here in the US).

Meanwhile, for the home theater, Dolby Vision supports the Rec. 2020 color space, a bit depth of 12-bits, and a current max output of 4,000 nits -- though future output could be upped to 10,000 nits. Unlike HDR10, Dolby Vision uses dynamic metadata and needs more specific hardware than HDR10, initially requiring displays to include a special Dolby Vision chipset (though recent developments have made software solutions a possibility).

Dolby Vision for the home theater is currently available on several displays from manufacturers like VIZIO, LG, and Sony. On the content side, Dolby Vision is an optional addition for HDR on Ultra HD Blu-rays. Lionsgate, Universal, and Warner Bros. have all announced plans to master Ultra HD Blu-rays with Dolby Vision, with the first titles announced so far being Despicable Me and Despicable Me 2. In addition, Dolby Vision content is also available through streaming services like Netflix and VUDU.

In order to watch Dolby Vision content, users will need a Dolby Vision-capable display along with a Dolby Vision capable Ultra HD Blu-ray player or set-top box. Unlike HDR10, Dolby Vision only requires HDMI 1.4 connections, but copy-protected content still needs HDCP 2.2 compliancy. At this time, it remains to be seen whether HDMI 2.0a receivers will be able to pass-through Dolby Vision video (at the very least, firmware updates will be required).

ADDITIONAL HDR FORMATS


Outside of the main HDR10 and Dolby Vision standards there are few other emerging high dynamic range formats as well. Most notably, there is the Hybrid Log Gamma, or HLG, standard developed by the BBC and NHK. The royalty free HDR format is geared toward delivering high dynamic range content over live broadcasts. And unlike other formats, HLG's HDR process doesn't actually use any type of metadata. So far, LG and Sony have confirmed HLG support for select 4K displays.

In addition, Technicolor's Advanced HDR solution is also geared toward broadcast high dynamic range, along with SDR to HDR conversion. According to Technicolor, Advanced HDR is actually "format agnostic and can take all HDR formats, as well as SDR formats, as inputs and then normalize and deliver all of them on any HDR or SDR device, ensuring a consistent experience in both HDR and SDR worlds." The tech is a combination of Technicolor HDR ITM which up-converts SDR to HDR, and Technicolor HDR which is able to distribute HDR and SDR content through one stream. So far, LG is the only manufacturer to make mention of Technicolor Advanced HDR support for its 2017 displays.  

RECOMMENDED GEAR


There are currently several great HDR display solutions on the market, covering a wide-range of price points and panel technologies. Here's a rundown of some recommended HDR gear available now...

65" VIZIO P-Series Ultra HD HDR Home Theater Display ($1,600) - This affordable yet high-performance Ultra HD display from VIZIO includes HDR10 and Dolby Vision support with 600 nits, along with full-array local dimming with 128 zones, and wide color gamut support. With that said, the display does not include a TV tuner. 

65" LG B6 OLED Ultra HD TV ($2,997) - This premium OLED display features HDR10 & Dolby Vision support with wide color gamut playback and Ultra HD Premium Certification. Thanks to its industry-leading black levels, this is one of the best-looking flat-screen displays on the market.

65" Class Q8C Curved QLED 4K TV  ($4,798) - As one of Samsung's top-of-the-line QLED TVs, this quantum dot curved-screen model offers HDR10 support (but not Dolby Vision). The display is also one of the first with HDR10+ support. Wide color gamut playback is included as well along with a QLED peak luminance between 1,500 and 2,000 nits.

  


So, there you have it. Those are the basics of HDR. If you still have any questions about High Dynamic Range, please let us know in the forums! 

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