4K and 8K have a standard, does it matter?
By Chris Heinonen on
Just like Rec. 709 gave us the standards for HDTV, and Rec. 1886 is going to give us a standard for gamma, we now have a draft standard for 4K and 8K video for the home. While nothing in here is final at the moment, it gives us a good idea of what these formats might look like at home. So what are the key things that are contained here?
– 4K is going to be 3840×2160, or 4x current 1080p resolution, and not 4096 pixels wide as you find in theaters
– Support for up to 120Hz refresh rates, though I doubt we see this due to the incredible amount of bandwidth required for content
– Everything here is now progressive and not interlaced, so no more debates about 720p vs 1080i and which looks better as everything will be progressive
– The RGB primary points are much, much larger. Even larger than DCI and other color specifications.
– 10-bit or 12-bit support for Luma and Chroma data
– 4:4:4, 4:2:2 or 4:2:0 chroma subsampling is supported
Now what in there really matters? The best thing to me is the support for a much larger color gamut and for greater bit depth with encoding. The larger gamut is tricky as displaying that will require LED light sources or something else to display those images. Most displays now can’t do that, even if they are 4K, so we will see how this progresses. The larger bit-depth for luma and chroma will lead to smoother gradients, better shading, and more detail in images. Both of these are far more important to me than 4K, where you need to have a display that is massive and that you sit very close to in order to reap all the benefits.
The big question is how will this content be delivered? We can look at the DCI standard to get a good idea of how this might work. DCI uses 4K resolution, 12-bits per pixel for color data, and progressive frame rates and has a maximum bit-rate of 250 mbit/second. It also uses JPEG2000 compression which is more advanced than the compression standards currently used for Blu-ray content, which allows them to save space and still have higher image quality. JPEG2000 might not have been possible when Blu-ray was designed, due to encoding or decoding hardware at the time, or it just was not considered necessary with the resolution and color depth of Blu-ray.
If we want similar image quality compared to Blu-ray, we’re going to be storing 4x the resolution, as well as 50% more bits per pixel, so we are talking about films that are 6x as large on average. With a Blu-ray disc holding up to 50 GB currently, that means we might have 300 GB films in the future to distribute. Some of that will be made up using more advanced compression techniques, and we could also shift to more advanced optical media, like BDXL, that allow for 128 GB on a disc. Given that this won’t be distributed for a few more years still, that allows for plenty of time to have a new optical media that can support this extra resolution and color depth for consumers to benefit from 4K.
How they are going to provide this over cable or OTA is beyond me at this point. Our airwaves are already full at this point from HDTV, and if you get HDTV from your cable or satellite provider it is currently compressed by a huge amount to save space. Asking them to send a signal with 12x as much data (since it is now progressive instead of interlaced, remember) is asking them to possibly choose between 12 cable channels or a single 4K channel. Our Internet connections also are not ready to handle this at the moment, especially with Comcast and other providers offering data caps of 300 GB which equates out to 1-2 movies a month in 4K, much less streaming content.
So 4K and 8K are in the future, with a specification now laid down for them, but there is far more to them than just more resolution. Hopefully we will start to see 1080p displays in the future that will support this larger color gamut and more bits per pixel, as even without the higher resolution you can still see a huge benefit from these features. Scaling the image down to 1080p for your display while keeping these features in place will still provide an image far beyond what Blu-ray or HDTV signals can do today, and hopefully we will see that at home soon.
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