Bruce's Thoughts on PS3 Horizontal Scaling in SDK Monday, January 29 2007
Some of you might remember I pinged Bruce Dawson (one of our senior software design engineers here) earlier with some questions around 1080i and 1080p. At the time I was trying to understand where Sony was coming from with all their "TrueHD" talk, especially as the 360 had just enabled 1080p output as well.
Anyway, last week we heard the news that the PS3 had fixed scaling on 480i PS2 titles running in backwards compatibility mode. This is a good thing. But we also heard that the PS3 SDK had been updated to allow PS3 titles to scale their content, but only horizontally. This is a weird thing.
I couldn't wrap my head around all the technical implications here, so I asked Bruce for his thoughts. Since there's nothing confidential here, I thought I'd share what he sent me. He knows his stuff, so if you find something you strongly disagree with or just want to ask a question on, add a comment to the discussion. I'll ask Bruce to swing by and answer as he has the time. Bruce's thoughts follow:
I see no sign that the PS3 contains a chip that can do vertical scaling, and this new feature (horizontal scaling) is a poor substitute for a true hardware scaler. It is a step forward for owners of 1080i only HDTVs, once PS3 games support it, but it is nowhere near as good as the Xbox 360’s scaler.
This recent announcement is just for horizontal scaling, and horizontal scaling is easy. To do high quality horizontal scaling you just need to buffer up a few pixels and intelligently average between them.
Cheap horizontal scaling is even easier: you just send pixels to the video output a bit slower (or send pixels at the same rate, but read them from memory slower). It’s the sort of thing that consoles have always been able to do. This new horizontal scaling feature just sounds like they are adjusting the video output rate.
Vertical scaling, on the other hand, is much harder. You need to be able to buffer up (or sample from) two or more lines of data, and then intelligently average between them. For high quality scaling you want to be sampling from a half-dozen lines or more. The Xbox 360 can do this. I don’t know whether the PS3 can do this, but if it could I think we would have seen it by now.
This new feature means that games that have previously only supported 720p can now, sort of, be modified to support 1080. When these games detect a display that can’t support 720p they can switch to using a 960x1080 buffer. This is only 12.5% more pixels than 1280x720 so the increase in fill rate and memory consumption should be manageable. Then they can tell the PS3 to stretch this buffer to 1920x1080 at display time and voila, 1080 support.
Except, it will be pretty weak 1080 support with an odd and substandard result. The horizontal resolution will be worse than with 720p (960 across instead of 1280), and the images will be twice as blurry horizontally as vertically. 960x1080 is going to look worse than 1280x720 (although it’s certainly an improvement over having to drop back to 480i).
I had figured that Sony didn't somehow manage to hide a hardware scaler from the general public and that there had to be some sort of trick to it.
If Bruce is right, then that may explain it. Regardless, for bringing this tidbit to light, you may get some flaming from the PS3 fanboys =).
Regardless, at least it is some sort of fix for the 480p/1080i owners which is a step in the right direction.