Dolby Vision and HDR10 enable amazing new video viewing experiences with a wider color gamut and deeper contrast. Learn how this new technology works, and what the differences are between Dolby Vision and HDR10.
With the introduction of the revolutionary iPhone X
and Apple TV 4K,
the video experience is taken to a whole new level
with the addition of support for high dynamic range video.
With HD, you only see 16 million colors.
But with HDR, you see one billion colors.
HDR allows content creators
to use a much richer and vibrant color palette,
which results in unbelievable and stunning image quality.
To better understand how HDR works,
let's first take a look
at the evolution in color capabilities.
Here is a representation of the visible color spectrum.
With the introduction of HD in 1990,
the color space was defined in ITU Rec 709
and covered about 36 percent of the visible spectrum.
But, a lot has changed since 1990,
and since then, the P3 color space was introduced.
This color space is widely supported across our platforms
for all types of app content.
Then in 2012, Recommendation 2020
was introduced to define the color space
for Ultra High-Definition television,
which offers a much wider color space
that covers more than 75 percent of the visible spectrum.
Video content can now be delivered to supported devices
in any of these three color spaces,
enabling far more realistic and rich color reproduction.
But, the color space itself isn't the whole story.
The luminance range and settings of the target display
is also extremely important
and impacts how a given color is going to be perceived.
This combination of color space and luminance range
is often described as the color volume,
with the luminance values on a logarithmic scale.
With standard dynamic range content,
it is assumed that displays
offer a peak luminance of 100 nits,
yielding a relatively modest color volume.
However, HDR formats are designed to support displays
capable of up to 10,000 nits of peak luminance,
yielding a much richer color volume
for content creators to work with.
To further understand the impact of luminance,
let's take a look at a 100 percent red square
in the P3 color space.
If the brightness setting of the display is at about 50 percent,
the red square might look something like this.
However, if the brightness of the display is turned up,
the very same RGB value looks quite different
and more intense.
Similarly, if the brightness is turned down,
it looks much more dull.
As you can see in this illustration,
simply utilizing the RGB values without having control
or context of the luminance of the display
leads to vastly different color perception by the viewer.
This also doesn't take into account
other influencing factors such as the ambient light level
or the color temperature of the ambient light.
Another key goal of HDR is to help improve
consistency in playback across different displays.
In SDR video, the target display is assumed to be capable
of up to approximately 100 nits of peak brightness.
However, the actual capabilities of modern displays
far exceeds this value,
and so each display then attempts
to interpolate the appropriate brightness levels
to match its own luminance range.
This leads to all kinds of variance
in the appearance of a given video
across different displays, and in many cases,
a very loose interpretation of the original artistic intent.
Now that you have a basic understanding
of the key elements of color and luminance,
and some of the goals of HDR,
let's dig into the types of HDR video that we support.
We support two HDR standards: Dolby Vision and HDR10.
These two formats share some common principles,
but also differ in many ways.
One of the commonalities between the formats
is how the luminance values are encoded.
Because the human eye is more sensitive
in dark ranges than light ranges,
the luminance values are encoded on a curve,
so that greater detail in darks
can be encoded using the limited bits available.
In SDR, the gamma curve was relatively shallow,
but this was sufficient
for the assumed peak target display luminance of 100 nits.
For HDR, a new luminance encoding curve
has been introduced.
Known as the Perceptual Quantizer,
it can better map these perceptible luminance changes
across the broader, 10,000 nit range.
This curve, described in SMPTE ST 2084,
allows for even smoother gradation
of dark luminance values,
yielding a far better experience for the viewer.
This curve is utilized by both Dolby Vision and HDR10.
In HDR10, a static set of metadata
is included in the video stream.
This metadata includes information about the display
on which the content was originally mastered,
such as its effective color gamut, white point,
and luminance range.
It also includes information about the content itself,
namely the peak and average luminance levels.
This metadata can then be used by the target display
to tone map the content to the output capabilities
of the display.
With HDR10, the metadata is applied
to the entire length of the program.
Dolby Vision gives you even more control,
allowing for metadata to be conveyed dynamically
on a scene-by-scene, or even frame-by-frame basis.
This way, the available luminance range of the display
can be optimized throughout a program
that might include both very dark and very bright scenes.
The format also carries a much broader metadata set,
further enabling the target display
to perform much more detailed tone mapping
and detail management.
Finally, Dolby operates a certification program
to ensure that each Dolby Vision capable display is consistent,
so content will always be displayed as intended.
For more information on authoring your HDR content
for delivery to supported devices,
please visit our HTTP Live Streaming developer page
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