Camp, it is true that a progressively-scanned image will bypass a TV's line-doubler. I think what Dave is saying is that if your TV has a high-quality line-doubler, there won't be as big a difference between the progressively-scanned image and an interlaced image that has been doubled by your TV. Whereas if your TV has a crummy doubler, the difference between the two can be much more apparent.
I think a progressive image will always look a little better; how much better is determined by how well your TV's line doubler re-integrates in interlaced signal. For the record, on my Pioneer the difference is slight, but noticeable when comparing the two images back-to-back. If you snuck in my house and switched my Xbox to interlaced, I doubt I would notice when I booted it up to play.
what Dave meant is that when the 480i signal is linedoubled by a very good deinterlacer, the difference to the 'pure' native 480p signal will obviously be less than when a bad-to-average deinterlacer is used on the 480i signal, or the 480i signal is even displayed interlace to begin with.
But even the best deinterlacer isn't able to get the same detail out of the 480i signal that is present in the 480p. This has 3 reasons:
1) The interlace signal is filtered quite a bit vertically, to minimize 'interlace-flicker'. The loss in detail through this filtering can't be reconstructed.
2) The interlace signal also isn't quite as detailed horizontally. The rise-time of the progressive signal is quite i bit higher, leading to more clarity. This is most likely not due to filtering, but rather due to the frequency response characteristics of the RAMDAC when displaying interlace content.
3) On film-based DVD, you get the full 24 frames of 720x480 pixels after you perform inverse 3:2 pulldown.
On video-based DVD, you have 60 interleaved fields of half resolution (720x240) in the 480i signal and you can use clever deinterlacing to minimize combing or bobbing artefacts.
The progressive output of the XBox on the other hand does have 60 full fields of full resolution (720x480 or 640x480). So its twice as much data to begin with. No deinterlacer can reconstruct this information.
On a revealing setup like mine, XBox progressive 480p looks MUCH better than 480i deinterlaced through even the most expensive scalers. I use the Key Digital CVC-A2 transcoder to convert the component output to RGBHV.
If have also seen a significant improvement on several other RPTV or FP setups. Whether your setup will benefit as much as mine, i can't tell obviously. But the signal IS that much better, given the proper circumstances.
P.S. When i have a nasty mood, i might post screenshots of games like Halo or Rallisport on my setup
To 3) again. My point here is, that the native progressive output of a DVD player uses 3:2 frame padding to output 60hz. This means there are only 24 actual 720x480 frames contained, the rest is repeated redundacy. The interlace output also contains all of these frames, you simply need to 'fit the fields together' properly. So an almost perfect reconstruction is possible.
But the XBox progressive output differs from that DVD progressive output in that it really has 60 full 640x480 frames in it and NO redundacy. The interlace signal always only outputs HALF of that information (60 fields of 640x240), although everything is rendered.
This missing half of information can't be restored, no matter what, which makes the advantage of XBox progressive output a totally different animal from DVD progressive output.
Dave & Bjoern - thanks! That's exactly what I meant. And thanks for the information regarding the differences between line doubling the a DVD output and a videogame. I had heard that it was very different with a videogame, but never gave it much thought. Your explanation makes a lot of sense.