Yesterday the Blu-ray Disc Association formally completed the Ultra HD Blu-ray specification. The specification has been under development for some time, with the first information about it being released in September of last year. The new specification allows for higher resolutions, a greater range of colors, and larger capacity disks in order to store a new generation of Ultra HD content.

The biggest point of the new Ultra HD Blu-ray specification lies in its name. Ultra HD Blu-ray will support the 3840x2160 Ultra HD resolution that has become standard across so called "4K" or Ultra HD televisions. That being said, an increase in resolution is not the only important part of the Ultra HD Blu-ray spec. The Ultra HD content standard, more accurately known as BT.2020, defines various aspects that go beyond resolution, including color gamut, color bit depth, and frame rate.

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In my view, the most important aspect of the BT. 2020 standard is the use of the Rec. 2020 color gamut. The color gamut that has been used for basically all picture and video content for quite some time now is called Rec. 709 or sRGB. sRGB is actually quite a narrow gamut, and has an lower overall number of colors than even the NTSC (1953) gamut that was used for video content before it. The Ultra HD specification uses the much larger Rec. 2020 color gamut, which will allow for colors of greater saturation to be reproduced. You can see this in the image above, with sRGB being the smaller triangle, and Rec. 2020 being the larger triangle that surrounds it.

In order to support the larger Rec. 2020 color gamut without introducing color banding, a higher bit depth is required. This is because a greater number of discrete colors will be required to display gradations that span a greater range of saturations. Ultra HD Blu-ray supports 10bit per channel color depth for content that uses Rec. 2020 for its color encoding. This moves the number of possible colors that can be displayed from approximately 16.7 million to 1.07 billion. I think it would have been better to use 10bit color for sRGB content and 12bit color for Rec. 2020 content, as current 8bit sRGB content can already experience noticeable color banding, but it looks like the additional space and hardware support required have not been deemed worth it.

While the new Ultra HD Blu-ray standard supports the existing 50GB capacity for Blu-ray disks, there will be disks of greater capacity for content that requires higher bitrates. 50GB disks will have video encoded at up to 82Mbps, while 66GB disks can support up to 108Mbps, and 100GB disks support 128Mbps. In order to encode videos with these high resolutions, bitrates, and greater color depth, Ultra HD Blu-ray will make use of HEVC video encoding.

While the appeal of physical media such as Blu-ray is in decline due to the rise of streaming media, it's still the go-to for users who care about having the highest possible visual quality. It will definitely take time for Ultra HD Blu-ray to be adopted in the market, and possibly longer for Ultra HD TVs that actually support the Rec. 2020 color space. It will be interesting to see where the market for movies and TV shows moves in the future, and what position physical media will be in at that time.

Source: Blu-ray Association (via Tech Report)

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  • auralcircuitry - Wednesday, May 13, 2015 - link

    How does this color definition differ (if at all) from the Dolby Vision spec? If TVs start to incorporate one or the other will it matter?
  • Brandon Chester - Wednesday, May 13, 2015 - link

    Dolby Vision uses Rec. 2020 so it shouldn't matter what it's branded as.
  • dragonsqrrl - Wednesday, May 13, 2015 - link

    66GB discs? I'm guessing that's the dual layer version of BDXL?
  • Ryan Smith - Wednesday, May 13, 2015 - link

    Correct. 2 layers for 66GB, 3 layers for 100GB.
  • chucky2 - Wednesday, May 13, 2015 - link

    So has it actually been confirmed that the underlying format is BDXL? Does this mean that existing BDXL drives will be capable of properly reading a Ultra HD Blu-ray?
  • Ryan Smith - Wednesday, May 13, 2015 - link

    So far I have not seen any information to confirm that.
  • Murloc - Thursday, May 14, 2015 - link

    absolutely not a given, maybe a firmware upgrade will do it, or maybe the hardware just can't do UHD and you have to upgrade....
  • herocero - Wednesday, May 13, 2015 - link

    I buy discs for movies where I care about SOUND. any changes in the ultra spec I can drool over?
  • phoenix_rizzen - Wednesday, May 13, 2015 - link

    Object-based sound systems like Dolby Atmos and digital something or other are included.
  • cmdrdredd - Wednesday, May 13, 2015 - link

    I read elsewhere that it includes support for Dolby Atmos and DTS:X Lossless formats.

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