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Thread: Some Truth About UltraHD/4K and Compression

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    Official HDJ Industry Insider AndrewRobinsonOnline's Avatar
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    Default Some Truth About UltraHD/4K and Compression

    werthliving.com

    Originally published on my personal site.

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    The impending release of UltraHD or UHD (aka consumer 4K) has many enthusiasts both excited as well as confused. Those that are excited believe it (UltraHD) will solve whatever problem they believe they’re having at the display level while others look at it and ask, what’s it all about -or perhaps what’s it all for? More people probably ask me about UltraHD and 4K these days over any other topic facing the specialty and even pro video space. Sadly, I don’t have all the answers and those that should -i.e. the manufacturers and technology creators -are being purposely vague. Why? Because there is still so much left to determine. So what do we know?

    We know this, UltraHD/UHD/4K is coming to our homes with displays capable of displaying such resolutions supposedly being available as early as summer, though more realistically late fall early winter. First generation sets are bound to be cost prohibitive for the masses with prices ranging from just over $10,000 on up to over $30,000. Many of the displays will be large 70-plus inches diagonally, though most will likely not exceed 85-inches at first. When 40-60 inch displays begin to hit the market the prices should drop dramatically as the average TV size in the US is NOT 70 plus inches but rather somewhere in the vicinity of 47. But do you need it?

    To understand that part of the question you must understand the difference between HD and UltraHD/UHD/4K. First, UltraHD/UHD/4K are all basically the same thing. Keep in mind we’re discussing UltraHD/4K ONLY as it pertains to the consumer marketplace right now, so yes, UltraHD, UHD and 4K are, in truth, going to be the same. And that is not where the similarities stop. For starters, let’s look at HD, but rather than break down all of HD’s many variations let’s focus on its best, which is Blu-ray.

    Blu-ray is a high-definition disc format that is capable of holding files ranging in size between 25 and 50GB. There are larger capacity Blu-ray discs coming to market, however they’re predominantly found in the computer markets not in the specialty AV ones. So for the sake of this discussion we’re going to stick with the consumer form of Blu-ray. Blu-ray is an HD format, arguably its best, and as such has a maximum resolution of 1,920 x 1,080 pixels. Frame rates can reach up to 60 frames per second (59.94 to be exact) though the common frame rate for movies is 24p or 24 frames per second progressive. Bit rates can reach as high as up to 48Mbit/second though they’re most commonly found to be limited to 36Mbit/second, which is sufficient, not to mention stable. Audio plays a role in this equation too as Blu-ray can encapsulate “uncompressed” audio codecs such as Dolby TrueHD and DTS-HD Master Audio, but assuming UltraHD/UHD/4K format will too let’s let audio be for the moment.

    Getting back to the Blu-ray standard, the compression codec most commonly used are H.262/MPEG-2, H.264/MPEG-4 and VC-1. You don’t have to know what these mean though know that H.264/MPEG-4 is arguably the most common and will play a role later in this discussion. Lastly, the format itself is an 8-bit format, with a color space known as Rec. 709. So in summation Blu-ray is; HD (1,920 x 1,080) at 24 frames per second, with up to 36Mbit/second data rates using H.264/MPEG-4 encoding with Rec. 709 sampled at 8-bit 4:2:0 all on a 50GB disc. That’s Blu-ray as it stands today.

    Now, it is important to understand that many of the above referenced variables are independent of one another. For example; resolution, i.e. pixels, have ZERO influence over color. However, compression, i.e. H.264/MPEG-4, can have an effect on transfer rates, capacity etc, thus making compression far more important a variable than say resolution. I mention this for two reasons; one, current UltraHD marketing is hammering home the importance of resolution and two, everything moving forward in the video realm -from capture to exhibition -is going to be about compression. With that being said, let’s look at UltraHD.

    UltraHD is the consumer format of D-Cinema or Cinema 4K. Since the consumer format is but a vague facsimile (at present) of true Cinema 4K let’s not waste too much time discussing Cinema 4K and instead focus upon UltraHD/UHD/ consumer 4K. Here’s what we know so far, UltraHD is four times the resolution (not quality) of HD. Meaning it has a native resolution of 3,840 x 2,160 pixels. The reason for UltraHD’s perfect four times pixel count has to do with the aspect ratio 16:9, which allows for HD (1,920 x 1,080) to scale proportionately to UltraHD or 3,840 x 2,160. It’s clean. It’s simple. UltraHD can also encompass the even higher resolution known as 8K, but let’s ignore that for now as it is even further away than consumer 4K. Now, from here things become a bit more vague -at least at this stage in the game. There is the possibility that UltraHD/4K, in the consumer realm, could include a broader color space, greater frame rates and higher bit depths. I say it could however, at present, all signs are pointing to it not doing those things for one reason and one reason alone -file size.

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    Last edited by AndrewRobinsonOnline; 02-02-2013 at 08:35 AM.

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    Default Re: Some Truth About UltraHD/4K and Compression

    Color space does not affect data rate and therefore should not affect file size. Displays would have to support it for accurate reproduction, however.

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    Default Re: Some Truth About UltraHD/4K and Compression

    You would be correct (if memory serves me), however I don't believe I specifically said that color space directly affected data rate but rather than increasing various aspects of the HD standard to that of Cinema-4K would result in larger file sizes. I may need to clarify my statements a bit better, however, increasing bit depth, color sampling and such would result in a larger file or require more compression be applied.

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    Default Re: Some Truth About UltraHD/4K and Compression

    I thought it was generally accepted that H.265 would be used for UltraHD which would provide better compression?
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    Default Re: Some Truth About UltraHD/4K and Compression

    h.265 is (reportedly) a better compression scheme than its predecessor, h.264. However it (again, reportedly) is more advanced in that it can keep quality the same as what we've grown used to with HD (Blu-ray) and streaming (name your service who uses h.264) but with dramatically smaller file sizes. It's also sophisticated enough to provide for more resolution, more color etc, however, going up in "quality" will mean that more compression will then have to be applied and not less. Look for bit rates to drop dramatically from the 20-30 Mbps we enjoy now with Blu-ray to most likely 15 or less with h.265. Remember, to a certain extent, we're squeezing better quality (reportedly) through an infrastructure that is already in existence. While new players (and displays) might have to be adopted if h.265 takes hold and is the backbone to a new physical format, with regards to streaming it needs to be small enough to stream via our existing pipeline.

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    Default Re: Some Truth About UltraHD/4K and Compression


    We would like to run that review here as well.
    zoha

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