Tech Analysis: 4K gaming on PlayStation 4 Pro

It all seems to have rather gone rather quiet for PlayStation 4 Pro, mere weeks before the system's launch. What's clear is that anyone who didn't attend the PlayStation Meeting in person a couple of weeks back still hasn't seen much of what the system is capable of. Follow-up downloadable media released in the wake of the event has mostly been bereft of quality and doesn't showcase the hardware favourably. Meanwhile, the first public reveal of the system at EGX recently was limited to just six units running just one title - Call of Duty: Infinite Warfare.

With just over a month to go before the new console launches, the lack of exposure for the system is puzzling. There are many reasons to be optimistic about the hardware's chances, principally because the software I've seen - principally Days Gone and Horizon Zero Dawn - looks impressive. They're not launch titles, of course, but they perhaps hint at the kind of quality we may see more generally a couple of months on from release. More than that, the price-point of the PlayStation Pro - $399/£349 - makes the hardware a no-brainer for new console buyers as we move into the holiday season.

The bottom line is this. While we can fully expect bundling deals and special offers to drive down prices on existing hardware, the retail pricing for PS4 Pro is undeniably compelling - $100/£100 more than the new CUH-2000 'Slim' PlayStation 4 model buys you 31 per cent of extra CPU power, 2.3x the GPU grunt, faster RAM and twice the storage space. As things stand, the base PS4 is suddenly looking very expensive for what it offers, relatively.

How PS4 Pro connects to your display

Connectivity between PS4 Pro and a 4K screen is very simple. In the resolution area of the video output settings, two new options join the existing 720p, 1080i and 1080p selectables. These are, in turn, 2160p YUV420 and 2160p RGB.

2160p YUV420 is interesting in that this allows PS4 Pro to connect to older 4K screens that lack the full HDMI 2.0 implementation. By reducing chroma information, the required bandwidth drops down in half, allowing HDMI 1.4 screens to get a full 60Hz signal.

The compromise is that hard reds, blues and greens can show low resolution artefacting. However, in our tests, we've found that it's not an issue in a typical living room environment. 2160p RGB doubles the bandwidth requirement, meaning HDMI 2.0 is a must, and sends the framebuffer through losslessly to the 4K screen.

What's curious here is that PlayStation VR's external processing box only seems to support HDMI 1.4, meaning that Pro functionality is limited to 2160p YUV420 - and HDR won't work either. Both 2160p RGB and HDR will require PSVR users to disconnect the external processor and hook up the console directly to the screen. This is not ideal, obviously.

If it all sounds like a bit of a minefield, another new option is added to PS4 Pro's video output settings, called 'video output information'. Selecting this confirms the resolution and colour format (RGB etc) of the connected display, and whether HDR is supported or not. The HDCP level of the screen is also revealed. If an HDMI 1.4 receiver is detected, you are warned that certain 4K material (we assume video streaming from the likes of Netflix etc) may not display at 4K.

A new HDR option has recently been added to the front-end of all consoles, and we've quickly tested Deus Ex: Mankind Divided on the base PS4. It is outputting a 1080p signal with HDR information to the display - a standard we weren't even aware of as existing until recently. We believe that it may be a recent addition to the HDMI 2.0b spec, and it requires that the PS4 is placed in full-range RGB output mode in order to work (we saw a very washed out image in limited range mode).

By pricing PlayStation 4 Pro in line with the original PS4's launch cost, Sony has realised that there's a certain price ceiling acceptable for a mainstream console launch, and while the omission of the UHD Blu-ray drive is a bad move for a device aimed at the higher end, more discerning user, it's clearly a business decision aimed at getting as many consoles into homes as quickly as possible. Keeping the price low also helps to address the key concern about the hardware, which is pretty simple: to what extent does it actually improve the visual experience? Before addressing that, it's worth pointing out that the relatively small price bump from PS4 to Pro means that even if you're buying just for more refined performance, excellent anti-aliasing and 2x the storage, you're still not getting a bad deal.

And that's important, because the pitch Sony has made has - at best - been rather shaky thus far. And what's concerning is that Microsoft's Project Scorpio proposition is basically the same. While both platform holders are giving developers carte blanche to use the new hardware as they see fit in terms of enhancing their games, the basic aim of the new kit is all about running existing games at higher resolutions, leveraging the advantages offered by 4K screens. The difference is, essentially, about pixel counts - as became clear in the recent Eurogamer interview with Microsoft.

"[Sony is] talking about checkerboard rendering and up-scaling and things like that," says Microsoft's Albert Penello. "There are just a lot of asterisks in their marketing around 4K, which is interesting because when we thought about what spec we wanted for Scorpio, we were very clear we wanted developers to take their Xbox One engines and render them in native, true 4K. That was why we picked the number, that's why we have the memory bandwidth we have, that's why we have the teraflops we have, because it's what we heard from game developers was required to achieve native 4K."

What you won't hear from Sony or Microsoft are the magic words - 60 frames per second - because fundamentally, both PlayStation 4 Pro and Scorpio are based on a similar technological base with the same key limitation in place: a hard and fast lack of choice on available x86 CPU technology. Hopes linger that Scorpio utilises AMD's new Zen architecture, but having already announced eight CPU cores in its next console, this seems highly unlikely. AMD's own eight-core Zen CPU targets Intel's high-end Broadwell-E processor as competition - and those processors start at $400/£400.

The attempt to sell a mid-gen console refresh is therefore based on the idea of the user owning or upgrading to a 4K screen - something that's very hard to market to users who don't own the technology. On top of that, it really helps if you own the right 4K display, principally one that supports high dynamic range. Oh, and do make sure that it's the right HDR screen. Many otherwise excellent screens accept the input, then scale it back to SDR - rather like the Samsung KU6400 we reviewed yesterday. Others support HDR, but aren't particularly bright, meaning you need to play in a darkened room to get the best effect. Meanwhile, some of the best and the brightest HDR screens - such as the Samsung KS8000 series - don't support low latency game modes when working with HDR content, adding over 100ms to lag. It's a minefield.

The question boils down to this: is 4K really worth it? And the answer to that is pretty straightforward - it definitely is. The detail increase is profound in its own right and moves into a different level entirely with HDR engaged. And the notion of a £350/$400 box able to service this resolution effectively represents a phenomenal value proposition, when a PC capable of doing the same job costs at least twice as much. However, In terms of enticing users towards upgrading their displays, much work remains to be done. All of the 4K content seen at the PlayStation Meeting is clearly and obviously a substantial visual upgrade over 1080p, even if it isn't actually native 4K. Sony's approach with the PS4 Pro is to treat ultra HD as a canvas for higher resolution gameplay, as opposed to a hard and fast pixel count that must be adhered to at all times.

The quality of the upscaling varies on a title by title basis, but at its best, in living room conditions, it looks close to native. The principle behind the 'checkerboard' scaling is pretty straightforward - a 2x2 pixel structure is extrapolated up to 4x4, apparently using new hardware built into PS4 Pro's GPU, so there is no cost to developers. The real question is how the hardware does the job.

Mark Cerny is apparently going to reveal more soon, but we're currently inclined to believe that a temporal component is involved - that information from previous frames is collated and used to help extrapolate the additional pixels. Perhaps we're looking at a more refined, non-interlaced version of the kind of technique used in Killzone Shadowfall's temporal upscaling. There's more evidence of this in Call of Duty: Infinite Warfare. Playing the game at EGX on PS4 Pro hardware, Tom Morgan and John Linneman noted a perfectly mapped 4K output on static scenes, with some checkerboard fringing in motion. Owing to the extreme pixel density of 4K displays, the artefacts aren't so intrusive in motion.

Returning to the PlayStation Meeting, Horizon and Days Gone really were the highlights in terms of producing a 4K presentation that could pass as native, but Infamous First Light was also striking. Sucker Punch's title also revealed a potential limitation of the technique - I noted some fuzzy fringe artefacting on alpha effects where the checkerboard isn't fully filled out, and similarly I saw something that looked very similar on Nathan Drake's hair in the Uncharted 4 demo. The difference between the two was that the artefact seemed to persist on the Naughty Dog demo, whereas I only spotted the issue on Infamous when the game paused to drop into Photo Mode. The commonality here is that it's alpha effects that are affected.

We're also inclined to believe that checkerboarding can be used to scale up to an intermediate resolution - such as 1800p or thereabouts - before a standard upscale kicks in. This may explain the Deus Ex: Mankind Divided screenshot on this page. Pixel counting suggests a 7/8 pixel ratio, giving us 3360x1890. However, there are no checkerboard artefacts at all, initially leading us to think that's a simple, conventional upscale in place here. However, our hands-on time with Call of Duty showing just how good the technology works on static scenes suggests that this Deus Ex shot may have been taken from a relatively static image. It's certainly at odds with our perception of the title in motion at the PlayStation Meeting, where the artefacts were actually amplified by the game's overly intrusive sharpening filter. Another title that may combine checkerboarding and upscaling is Mass Effect Andromeda - though we really need better media to work with than is currently available.

But one comment in particular from a Sony developer I spoke to at the PlayStation Meeting stands out - that there's more to the PlayStation 4 Pro than the checkerboard upscaling alone, along with Mark Cerny's comment that the new hardware has "adopted many new features from the AMD Polaris architecture as well as several even beyond it". We already know that the revised AMD GCN cores available in the PS4 Pro are able to process two 16-bit floating point operations in the time taken for the base PS4 hardware to complete one, meaning that revised, Pro-optimised shader code can be much faster.

On top of this, we now understand that the Pro GPU includes custom hardware for accelerating virtual reality. While we're still chasing down the precise detail here, logical steps forward would be akin to what we've seen in Nvidia's hardware - stereo geometry processing, and multi-resolution shading. The latter in particular is a big deal: it would allow Pro developers to concentrate GPU resources on elements of the scene that are actually visible, as opposed to fully processing the periphery of the viewport, with resolution literally wasted in the final lens warp.

The question is really to what extent this is actually custom hardware developed by Sony, or whether we are looking at elements of AMD technology that have indeed been harvested from future Radeon kit. An interesting, albeit unverified report arrived this week discussing how the upcoming Vega architecture increases efficiency from the GCN shaders, and you can't help but wonder whether Sony already has access to this technology in the Pro based on what we've learned about the hardware so far. Similarly, we are curious about whether the relationship with AMD works both ways - the option to use checkerboarding in the PC space could be very interesting. With so many 23-inch and 27-inch 4K displays on the market, exhibiting extreme pixel densities, checkerboarding artefacts would be very hard to pick up on, even in a desktop environment with the user closer to the screen.

More interesting is that the fundamentals of the GPU design are more ambitious than we previously believed. PS4's GPU effectively uses a modified version of the Pitcairn design used in the Radeon HD 7850 and HD 7870. Xbox One is based on the Bonaire Radeon HD 7790 and R7 260X. With that in mind, when it was revealed that PS4 Pro features 36 compute units, it seemed that Polaris 10 integration in the new PS4 Pro processor was a lock. However, what's clear is that the new console is different, more functionally rich in some respects and much more of a custom design than its predecessor. It also helps to explain why there is not an existing Radeon part (that we know of, at least) on the roadmap that's a good candidate for Project Scorpio's six teraflop GPU. PS4 and Xbox One were built in an era where the future of console hardware was in doubt, where both Sony and Microsoft were conservative in their designs compared to Xbox 360 and PS3. With PS4 Pro and Scorpio, both platform holders know that they have a strong userbase leading to more ambitious designs.

Thus far, everything we've seen so far suggests that the PS4 Pro is a really interesting piece of hardware, and we really can't wait to really put it through its paces. However, while remaining generally optimistic about the machine having seen some of its demos, there are some aspects where we should sound a note of caution. Firstly, while scaling up existing games to 4K (whether natively or via checkerboarding) inevitably leads to a cleaner, crisper, more impressive image than the base PS4's 1080p standard, it's our contention that other aspects of the presentation need to scale with it - and there have been signs that this could be challenging.

Our Rise of the Tomb Raider PS4 Pro vs PC comparison highlights that the new console lacks the memory to house the top-tier textures put together by Crystal Dynamics. Instead, the artwork is a match for the Xbox One title. By and large this is not a huge issue during gameplay, but the high-end artwork requires little in the way of additional GPU computational resources but clearly makes much more of the stratospheric pixel count. It's an enhancement that - fundamentally - is worth having, but the PS4 Pro retains the same 8GB of GDDR5 as its older sibling, meaning that mostly the same assets will be used as the base 1080p titles.

Secondly, my colleagues John Linneman and Tom Morgan noted that the EGX demo of Infinite Warfare on PS4 Pro hardware appeared to use low levels of anisotropic filtering - the same as the base PS4 version. Texture filtering and the lack of it is a continuing issue with current-gen consoles generally, and doesn't look great at 1080p. Clearly, it will be more of an issue at 4K, regardless of whether you're upscaling or rendering natively.

And finally, there's the issue of performance. We expect more from the Pro, but according to both John and Tom, the EGX demo of Call of Duty Infinite Warfare appeared to exhibit frame-rate drops more severe than the base version of the game. It should be pointed out that different content was running, and obviously the title may still have had development time remaining, but at the PlayStation Meeting, Deus Ex also seemed to run slower than the existing PS4 game. Assuming this is borne out in actual testing of final code, this is actually in breach of Sony's technical requirements for PS4 Pro titles. The platform holder has been stringent about upholding performance standards in PSVR so we hope the same applies to Pro software.

And this highlights another concern we have right now: even if we factor in PS4 Pro's enhancements, the fact is that generally speaking, boosting a GPU's compute capability needs to be matched with increased memory throughput to get the most out of it - and PS4 Pro's 25 per cent increase in bandwidth seems a little lackluster compared to the 2.3x boost to compute throughput. As a counter-point, we should point out that AMD's RX 480 competes well with the outgoing R9 390, despite a huge shortfall in memory bandwidth between the new hardware and the old.

All of which helps to puts the spec for Microsoft's Project Scorpio into perspective. The bandwidth boost we would expect is there, the additional compute power is there and unless the Xbox designers are using cutting-edge G5X memory, it'll have a 4GB memory advantage too. Certainly, the motherboard renderings revealed at E3 do seem to show 12 memory modules in a clamshell arrangement around the main processor, suggesting a 50 per cent uplift in memory allocation vs PS4 and Xbox One. Just as much of a giveaway is the fact that Microsoft is building games right now that include high detail artwork designed to look good on 4K displays, requiring more memory than you'll find in the standard Xbox One.

At the time of its initial reveal, the notion of Microsoft touting "the highest quality pixels" for Project Scorpio sounded ridiculous - and maybe the point was badly phrased - but we've always been clear that is that there is more to image quality than pixel count alone. Time and time again we've seen either very little difference in quality between two images with different resolutions, or Xbox One titles presenting more detail than PS4 equivalents owing to much improved anisotropic filtering.

"Higher quality pixels" - assuming we're referring to increased texture quality, decent anisotropic filtering and fewer post-processing compromises - may suggest that the next-gen console head-to-heads may be more interesting than the basic 1080p vs 900p differentials we tend to see in the here and now on current-gen console hardware. With PS4 Pro arriving imminently, we get the feeling it won't be too long before Microsoft shows Scorpio in action and at that point we should get a good measure of what the new Xbox offers. After all, the message from the Xbox team for the next 12 months is essentially going to be about how much more you could get by holding fire on a new console purchase. But the fundamental challenge remains in marketing what these machines are truly capable of, and it's equally applicable to both platform holders. We need to see 4K looking at its best, as a tangible upgrade to full HD, and somehow, we need a way of showing just how much HDR brings to the table. In a world of 1080p SDR screens, that isn't going to be easy.

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