They will have to have a Eureka moment to do it and think they are working on achieving just that. The only other option they have if they don't discover how to make it better is to dumb down the shadows.
We're basically in the realms of original research there, I think. Cue keynote speech and Gran Turismo 5 (patched) footage at the next SIGGRAPH event...
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GT:HD looks "better" in 1080p simply because its framebuffer is 1920 x 1080. We should compare it in 720p, that's where image quality and effects, scenery etc. will really make the difference, rather than absolute sharpness. I mean, I've seen GT4 running at full 1080p (emulator), it's pretty sharp, but it doesn't look better than GT5.
I think GT5 looks great overall. I can still be amazed by it when come back to the game and I see the demo running, after a short hiatus. Someone summed it up nicely earlier in the thread: it's
disappointing when you notice the little shortcomings in the scenery, but it's not game breaking. To be honest with you, I'm more annoyed by the colour compression that PD uses to save bandwidth costs. But I don't see anyone else complain about that!
The technical achievements have absolutely everything to do with the appearance of the game. Without them, it wouldn't look half as good, or we simply wouldn't have had certain features. I'm amazed that the Nürburgring looks the way it does - the game clearly only loads a small portion at a time, including the distant scenery "shell" and texture, then streams in and populates that area with the high-detail stuff as needed. That's why stuff tends to go missing, and is also the reason why pop-in is inconsistent and sometimes very jarring. To have that level of data-streaming going on at the same time the game is running 16 cars, and the graphics / effects looking the way they do is mind-boggling!
But, there's
always room for improvement. 👍