Why the PS3 framebuffer only scales horizontally

[pcflynn89]

So a few days ago, I asked what resolution MGS4 ran at and AlStrong, a mod here, pointed me towards this thread containing all known game resolutions, which was helpful and interesting. http://forum.beyond3d.com/showthread.php?t=46241

In that thread, AlStrong claims sony "gimped" the ps3 framebuffer to only horizontal scaling. I believe I found the reason why Sony has done this. In an interview with Studio Liverpool (makers of Wipeout HD - a game that runs 1080p60 at all times but uses dynamic resolution) Digital Foundry inquires how the dynamic resolution scaling works and why they do it.

Essentially, the framebuffer is adjusted in steps of +/- 32 pixels based on the complexity and render speed of the previous frame. By adjusting the horizontal resolution only, the game remains at "1080p60" as there are always 1080 lines of vertical pixels. At times when there is only 1 ship in view, the game really runs at full 1920x1080 at 60fps. When multiple ships are in view and lots of particle effects are happening (weapons, collisions) the game can scale all the way down to 1280. By scaling the horizontal resolution down, the framebuffer can decrease to almost the same size as a 720p frame, while keeping the vertical resolution of 1080. Interesting and pretty smart if you ask me.

The whole article is well worth a read and is very interesting. http://www.eurogamer.net/articles/digitalfoundry-wipeout-hd-fury-interview

Page 2 at the bottom discusses the horizontal scaling method.


Moral of the story: the ps3 scales horizontally because it allows for a closer-to-true 1080p.

 

[Shifty Geezer]

Except if they allowed arbitrary scaling, a developer could choose to just scale horizontally, while other developers wanting a full screen scale would also have access to that...

 

[T.B.]

Sorry, but these are two different things.
The scaling done in WipEout is not automatic, but something they do themselves. As far as I understood it, they even keep the GUI at 1080p at all times. They could just as well vary the vertical resolution.
As to why the scaler only works horizontally, I guess it's implemented to work per scan-line, although I vaguely remember something else going on...

 

[pcflynn89]

I would insinuate that by doing this, sony is pushing developers to make 1080p games.

I am new to this so be nice

They talk about the scaling in pretty good depth in that interview.

 

[Arwin]

The reason why the PS3 doesn't do more than horizontal scaling is basically because there's no dedicated scaling hardware on board. This horizontal scaling is something that if I remember correctly is supported by RSX exactly like that. Even then, the PS3 developers will have implemented both a 720 and a 1080 based output resolution, or some other form of "manual" scaling (usually upscaling), i.e. scaling in their engine.

This in contrast to the 360, which has a dedicated scaler chip on board (like most modern TVs) which allows games to mostly just target 720p and have people play that at most output resolutions out there, without developers having to worry about those resolutions.

 

[grandmaster]

Moral of the story: the ps3 scales horizontally because it allows for a closer-to-true 1080p.

No, AlStrong was right - the PS3 scaler really is gimped. If it wasn't, all games would play at a scaled 1080i/1080p resolution as they do on 360.

Sorry!

 

[TimothyFarrar]

Silly humans, perhaps extra hardware scaling can be a waste of Si when developers can sometimes render at a choice non-video-out-matching-resolution prior to the last full screen post render pass and up/down-sample then. BTW much easier to re-sample along a single scan line...

 

[AlNom]

Silly humans, perhaps extra hardware scaling can be a waste of Si when developers can sometimes render at a choice non-video-out-matching-resolution prior to the last full screen post render pass and up/down-sample then. BTW much easier to re-sample along a single scan line...

It can't be that much die space can it

On the other hand, the developer would have to have control over what the upscale/downscale target is according to the OS setting. The onus would be on the developer to detect that (if they can query that?) and scale how they want.

Dubious decisions as with Soul Calibur IV on 360, which is rendered at 1365x960 but software scaled to 720p no matter what, make me worry about leaving it up to the developer. If a person is using 1080p, the result is a second scaling (1365x960 ->720p ->1080p) as opposed to a direct scaling (1365x960 ->1080p); considering the 360 hardware would have done a single scaling automagically... one wonders what the heck they were thinking. :s

In light of other... certain... discussions... What would be the cost of a good image post-process (scaling and... say... morphological AA ) (of course, all subject to developer awareness ) Some cheapo scale would be trivial, but... something a bit more interesting than bi-cubic for those nasty edges...

 

[patsu]

It is probably because the hardware was designed without much consultation with the outside world. Only IBM, Sony and Toshiba engineers were involved.

 

[TimothyFarrar]

Actually I was being sarcastic about using the texture units to do up/down-sampling. Full screen passes can be on the order of a 1ms cost on the PS3. Not cool to use them unwisely.

 

[Gitaroo]

how are the scaling done when you play PS2 and PS1 games? Cuz some games that I play looks super clean compare to their own 480p option.

 

[Rangers]

It is probably because the hardware was designed without much consultation with the outside world. Only IBM, Sony and Toshiba engineers were involved.

Since it was based on a PC GPU wouldn't it just be a quirk of G70 that carried over to PS3?

Thats kind of how I always understood it. It was bugged in G70, so it was bugged in RSX.

 

[patsu]

I don't know. The PC GPU card drives computer monitors. PS3 drives assorted consumer TVs. Someone in Sony needs to be in charge of the overall end user experience. I see there is a dude in charge of PS3 hardware marketing in US, but I don't think he controls the PS3 design. It was done way before.

 

[joker454]

Thats kind of how I always understood it. It was bugged in G70, so it was bugged in RSX.

That's what I was told, basically that the silicon for scaling is there but it's bugged, producing bogus results when scaling vertically. NVidia has a history of shipping broken hardware so I guess it's not hugely surprising, like the old 6800's that were supposed to hardware accelerate video playback but oops it didn't work on the early ones that were sold. As for how Sony ended up with that particular rev of 7 series hardware is anyone's guess.

 

[patsu]

As for how Sony ended up with that particular rev of 7 series hardware is anyone's guess.

It could be any component. Basically if it's not in the specs, it won't be considered a requirement. If the product manager thinks the scaler is good enough, then it's good to go.

 

[AlNom]

Sony's maybe not too happy about that...

 

[patsu]

It's probably weighted against the BOM cost, and other factors. Somewhere inside here, we may fit a Super Companion Chip story/rumor.

Is the scaler a big problem ? I have a 1080p TV.

 

[Xenus]

Yeah that's why you need to spec out everything. If you don't tell someone you want to be able to do it and just assume it'll get done you end up with someone okaying something that didn't work for it.

 

[grandmaster]

It's probably weighted against the BOM cost, and other factors. Somewhere inside here, we may fit a Super Companion Chip story/rumor.

Is the scaler a big problem ? I have a 1080p TV.

It's a problem if you have a 1080i-only set, in that you're limited to 480p if the game has no 1080p framebuffer support. It's also a problem if you have a cheapo set with a crappy, laggy internal scaler. We're really going over old ground here but it is patently obvious that having an internal scaler that works on all games is clearly a desirable thing to have and if omitting is a deliberate design decision by Sony, it is somewhat short-sighted.

 

[patsu]

They pushed it to the software to handle via the horizaontal scaler. It may not cost extra for them since it's already in RSX built-in. Perhaps they think those old TVs will go away within the 10 years lifecycle (with OLED, 3DTV and other upcoming tech). They may have saved the money for other things like HDMI, Blu-ray, HDD, etc.

The problem is we don't have a face to associate these decisions with. No channel to understand/clarify their context. Makes it hard/impossible for Sony to connect with the consumers. All these may be potential (lost) opportunities for them to forge customer relationships.