Ultra HD Blues...and Reds and Greens
Are there advantages to be had from 4K resolution? Using the Sony projector on a 96-inch wide screen, I found that the 4K material I had on hand, courtesy of Sony’s FMP-X1 Media Player, was only marginally superior to the same material upconverted in the projector from 1080p Blu-ray to 3840 x 2160 (consumer “4K”). The 4K sources did offer a subtle but appealing improvement in smoothness and clarity, with no loss of fine details. But it took critical viewing under a direct A-B comparison to clearly see the differences.
A truly definitive A-B comparison of 4K vs. 1080p would require a 4K projector displaying 4K material vs. a 1080p projector with the same material in 1080p. But not just any projectors would do. The 1080p projector and program material would have to be absolutely identical, in all but resolution, to the 4K display and sources. The color, gamma, brightness, black level, lens quality, and a host of other factors would have to be indistinguishable between the two setups. We’d also need a variety of pristine sources, since the quality of any video presentation can be no better than the quality of the source material.
Such a rigidly controlled comparison is impossible in the consumer realm, and perhaps unlikely even on the pro side. We know of no 1080p projector or other type of display identical in every respect, apart from resolution, to a 4K sibling.
Both sources in my comparison were being viewed on the same 4K projector, so we might initially conclude from my observations that 4K sources may not really be needed. With consumer 4K sources and displays still in their infancy, I’m not quite ready to go there yet. But even if that were ultimately the case, it doesn’t rule out the possibility that a 4K display of sufficient size, showing cleanly upconverted 1080p material, might offer real advantages over a 1080p display. For example, a 4K projector, properly designed, must use superior optics to take full advantage of 4K sourcesoptics that will benefit upconverted 1080p as well. (If that suggests that it may be difficult to offer a cheap and good 4K projector, since a projector’s lens is a significant cost factor in its manufacture, well, there it is. Electronics have become cheaper over time; good lenses have not.)
But let’s assume for the sake of argument that true 4K resolution alone (including a 4K source) will not produce an improvement big enough to matter to most viewersat least on anything but a very large display. Are there any other possible benefits to Ultra HD from source to screen? The answer is yes, and it involves color.
Our current HD color system has three major limitations: 8-bit color depth, lossy color compression (color subsampling), and a color gamut well short of the limits of human vision. Most video displays work with a color depth higher than 8-bits, but those extra bits are interpolated and not present in the source. And while most HDTVs and projectors can produce a wider color gamut than the present REC709 HD standard, going beyond REC709 by setting the user controls to a wider gamut (an option available now on most HDTVs) will simply produce distorted color. The added colors are not in the source. The accompanying diagram shows both today's REC709 color gamut vs. REC2020. The latter is the widest of the gamuts being considered for Ultra HD, though whether such an extreme gamut is achievable with current technology is still an open question.
For those who may be wondering what the Ultra HD standard actually is for color, there isn’t oneor at least not one that’s fully complete and approved. While the Ultra HD sets currently on the market will all be able to display current (and likely future) 4K source resolution at up to 30 frames per second (the Sony 600ES is rated up to 60fps), there’s no guarantee that they’ll be able to take advantage of the enhanced color we might see in the final Ultra HD standard.
Note that the source material I viewed on the Sony projector had none of these possible future color enhancements. Despite its 4K resolution, the 600ES's color is identical in all respects except one to today’s REC709 HDTVs. The exception is x.v.Color (xvYCC), and the 600ES can take advantage of this feature if it's in the source. A limited range of sources that use x.v.Color is now available on a few Sony Blu-rays and some of the material on Sony’s 4K Media Player.
But x.v.Color is a different animal to the possible Ultra HD enhancements mentioned above. It can expand color to some extent, but it's not a color gamut. It's merely an extension of selected colors beyond the REC709 gamut. I didn't use x.v.Color in my viewing of the Sony, since selecting x.v.Color on that projector locks out all of the optional gamma selections. The one remaining gamma, in the Off position, was too low. I’d gladly give up the subtle enhancements of x.v.Color for the obvious advantages of the correct gamma. And in the review, I did.
So when we talk about possible color enhancements we might see in the final Ultra HD standard, we’re not talking about x.v.Color but rather about something altogether more revolutionary. But the road to reach them won’t be easy. Such enhancements will require a lot more storage space to accommodate the extra data needed for 4K resolution and enhanced color.
There’s a lot of chatter these days about 4K downloads being the way to go and the NextBigThing. But it’s also possible that a 4K download, given current bandwidth limitations, will look no better than a 1080p Blu-ray&$151;and very possibly worse. It will be sold to the eager public as 4K, but the improvement over a 1080p download might not be worth the candle.
To consistently achieve what Ultra HD might have to offer, without major compromises, we’ll need a new disc formathopefully one that’s backward compatible for 1080p playback with the millions of Blu-ray players already in consumer’s living rooms. But any such “Ultra Blu” format must remain a discussion for another time.
Whether the change to 4K, with resolution and color enhancements, will be a revolution as significant as was the transition from SD to HD is still an open question, though in my opinion it will not be as dramatic. That doesn’t mean I think it’s unimportant. I want all the improvements Ultra HD can offer, both subtle and obvious, as do all videophiles. But with video, as with any new technology, it’s the average consumer who will determine Ultra HD’s success or failure. The change from the current standard must be visible to everyone, and not just an attempt to shake up a margin-starved video market with a new buzzword.