Ok here is something that came to my mind after reading about a guy who built his own progressive scan DV camera:

We like proscan because it gives us 'film-like' motion and does not exhibit interlace artifacts, right? That's really cool and I like it too... but I also think there might be another reason to embrace proscan, a reason that makes it important for the camera to do real progressive, not post, not deinterlacing. The real thing.

As I seem to recall, the DV25 codec has no interframe compression, but seems to have some form of interfield compression. Of this is true, than having the same info written to both fields should yield a better image, right? Could that be as good a DV50@60i? If DV25 is said to have a compression ratio of 5:1, would using proscan be actually giving us something like 2.5:1 performance?

Yes, DV has not interframe compression. I'm thinking DV compresses
each frame seperately, but I'm not sure on that. If both fields
contain the same information then you would loose 50%
vertical resolution unless I'm missing something. I'm also not
seeing how this would decrease the compression level since
both fields will be compressed the same.

ignacio,

can you tell me where did you read about that guy who made his own progressve camera?

any links?

thank you

filip

Hmm, yes Rob, I had not though about that: each field is only supposed to have half the lines... if the bandwidth allocated for each frame is shared between two fields, then having similar info on both fields reduces compression artifacts but we will not really ever have the same info in each field, so it's not like having two exact same frames in an interframe compression scheme, thus we don't get a dramatic quality gain... probably just a very mild one.

Of course if we are compressing 'Sony-style' line-doubled 30 fps, both fields would have the same info and, as you say, we would have reduced vertical resolution and, as I believe, less compression artifacts. I guess I prefer real proscan though... (sigh)

Filip, the article on the home-built proscan camera is right here in another thread:
http://www.dvinfo.net/conf/showthread.php?threadid=21115

Both fields do not have the same information.

In progressive-scan, both fields are captured at the same moment in time, but contain very different data.

In interlaced, both fields are captured at different moments in time, and also contain very different data.

Right Barry, so basically, I was wrong :-)