“Not by sound alone”: How Dolby Vision makes the world brighter

We recently talked about Dolby Atmos technology (we discussed it in more detail in our podcast ), which brings new audio sensations when watching movies. In this regard, it is worth mentioning one more technology, which is the second component of Dolby Cinema - Dolby Vision.

Photo OgreBot / CC

Dolby Vision is the standard for high dynamic range (HDR) video. The essence of HDR video is not in high resolution; Realism is more accurate color and contrast than standard dynamic range (SDR). That is, the image becomes brighter, but only in the right places.
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About how this technology differs from HDR-photos can be read here . But if in brief - to get a wide dynamic range in the photo, you need several pictures taken with different settings. In the situation with video, the emphasis is on a more detailed display of images at the same time in bright and dark places.

What else is from HDR video

There are other standards developed by different companies. In general, they can be divided into two main subgroups: PQ (Perceptual Quantizer) and HLG (Hybrid Log Gamma) - the latter is developed jointly by the British BBC and the Japanese broadcaster NHK. Technology Dolby Vision, as well as standards Prime Single (from Technicolor and Philips) and HDR10 belong to the first group - PQ.

HDR10 and Dolby Vision support the technology of the electron-optical transfer function (EOTF), which was developed by Dolby. The Society of Film and Television Engineers (SMPTE) has standardized PQ technology called ST.2084.

HLG technology is used for television broadcasting, as it can combine SDR and HDR into one channel, and the required signal will be used depending on the receiver that the end user has. You can read more about HLG technology here , and we have already written about other types of HDR and how to use them in our blog .

But how does Dolby technology relate to other standards? In 2016, the UHD Alliance developed a new standard UHD Premium. Televisions that meet this standard, support 4K video, can give a brightness of at least 1000 nits, etc. This specification stipulates the use of different standards, including SMPTE ST.2084 and 2086, but what technology will be used depends on the choice of the manufacturer. Dolby Vision technology TVs must be labeled with a special logo. A list of specific devices is presented on the Dolby website on the Products tab .

TVs

In order to see the HDR image, you need a device that supports this format. SDR TVs are limited to the Rec.709 standard, and the image on them looks fainter. LCD and OLED displays may reflect the DCI-P3 cinema standard used by the HDR10. But Dolby Vision supports the Rec.2020 standard, which makes the color even more voluminous (of course, this is a subjective assessment).

Theoretically, a display that fully meets this standard could reproduce the full color saturation, which is 75% of the visible color spectrum. Only here there are no TVs that can fully convey such a color space. Today, Dolby Vision TVs, like the HDR10, only support approximately 90% of the wide color gamut of the DCI-P3 standard (which represents 42% of the visible spectrum).

So which displays are more suitable for Dolby Vision? There is no clear answer to this question. OLED TVs have one indisputable advantage - the perfect black level, which helps to achieve the desired contrast. On LCDs, black looks brighter. In addition, it was difficult to get a rich color on them, because of the filters used, which simply made the color darker, not brighter. But in modern LCD-TVs to achieve a wider color range (WCG) turned out thanks to the " quantum dots " (although at the moment it is rather a marketing name), therefore, Dolby Vision technology is quite compatible with these two types of displays.

But another difference that can be seen on the existing equipment is the difference in peak brightness. Dolby Vision can use brightness up to 10,000 nits, and devices with HDR10 have enough brightness of 4,000 nits. Dolby Vision can adapt to the screen of any brightness level, but it turns out that according to the characteristics of peak brightness and color spectrum, this technology is more promising.

A little more about color and brightness. On conventional televisions, 256 shades (8 bits) are available for each of the three primary colors. HDR uses 10 bit sampling, which is 1024 shades for each color. And the color depth of Dolby Vision images reaches 12 bits, although 10-bit sampling is recommended for home viewing. Due to this, bright areas begin to stand out and are perceived as more realistic. Compare the image of HDR10 and Dolby Vision on the example of a frame from “Mad Max” here .

Content

But the main difference between these two formats is not what devices are required for their transfer. Dolby technology is built in at all stages from content production to the moment of playback on a specific screen. During the creation of video content, the director and colorist work on it separately to achieve the desired colors. And the difficulty with HDR TVs is that they can change the palette at their discretion (depending on the algorithm). And guess what the picture will see the end viewer is almost impossible.

Dolby Vision solves this problem in the following way: when creating video content, colorists can use a control monitor developed by Dolby. Later, along with the signal to the TV that supports this technology, metadata is transmitted that tells the TV what the picture should be.

Unfortunately, there is not a lot of suitable content, but as we have already said, Dolby Vision and HDR10 are based on one ST.2084 standard. Therefore, content producers can first create video in HDR10, and then add dynamic metadata for Dolby Visio.

How Dolby technology influenced Star Wars: The Force Awakens:


But it is not necessary to wait for the release of new paintings. Many films shot in the last 10 years have a much wider dynamic range compared to what televisions were capable of displaying. Therefore, even old movies on new devices can "play with new colors."

Many streaming studios already support Dolby Vision, for example, Amazon Prime Video, Netflix and Vudu. And in 2017, a UHD Blu-ray player with Dolby Cinema technology will be released. You can find out which films were shot with the support of Dolby Vision and Dolby Atmos, and you can choose what to watch on streaming platforms on the Dolby website on the Movies & TV tab.

PS One more fresh material in our blog on GT - Entertaining music: Number 5 and a little about how a usability player and programmer "see" music .