Live Performance 720p v's 1080p

[David Heath]

Originally Posted by John Peterson

Several have argued that shooting 720p will produce a better SD DVD because less down conversion is required. And others argue differently. None of the threads have reached a definitive conclusion yet.

I think there has been a conclusion, but there are a few complications.

Main one is what sort of motion is needed - "film-look" (24-25fps), or "fluid motion" (50-60fps).

If the former, it's easy - shoot 1080p/25, there should be no argument. For the second, the choices are 720p/50 or 1080i/25, and I think the concensus is that if the SD DVD is the primary product, 720p/50 is better, because each progressive frame produces a unique SD field. Start off with 1080i/25 and it first has to be de-interlaced before downconversion - never a good idea - you cannot simply derive each SD field from the corresponding HD field.

If the HD version is the primary product, and fluid motion is desired, there may be a strong argument for 1080i/25, but then it's likely the SD version will be somewhat compromised compared to if the starting point had been 720p/50.

The future lies with 1080p/50, and all arguments should then go away...... :-)

[Bo Skelmose]

arghh... Sorry read and wrote it as SD and not SP - What I meant was that I have no SD modes on my ex-3...
I have tried with 720-50p also and I guess different NLE's does different downconvert to 50i - Premiere CS3 does not make a proper downconvert to 50i from 50p format - my experience is that 25p to 50 i makes a better downconvert in premiere but maybe it has to do with the settings.....

[Alister Chapman]

For SD you want either 50i or 25P. There is no standard 50P SD format which might be why Premiere is struggling.

As David says roll on 1080/50P... but sadly it's still going to be a couple of years at leat before it becomes common place.

[David Heath]

Originally Posted by Bo Skelmose

Premiere CS3 does not make a proper downconvert to 50i from 50p format -

My comments were meant generally, not for specific NLEs. But HD 50p *SHOULD* downconvert well to SD i25. There's a 1:1 releationship between the input HD frames and the output SD fields.

..........my experience is that 25p to 50 i makes a better downconvert in premiere but maybe it has to do with the settings.....

But 25p has film look motion (or "jerky", depending on point of view). A 50i (i25 in the new standard - the EBU decrees the numbers should always refer to frames) system indicates fluid motion, which a 25p starting point can never give.

[Andy Shipsides]

IMHO you should always shoot 1080p and downconvert later. Shoot 720p for slow motion and for scenes where you want to capture high speed motion. Otherwise shoot 1080p. To achieve 60p in 720 the camera is shooting at exactly half vertical resolution, so it isn't downconverting from 1080p to get 720p it is converting to 1280x720 from 1920x540.

I think that a final SD product will always look better when starting from the high resolution possible.

[Jeremy Hughes]

Originally Posted by Andy Shipsides

IMHO you should always shoot 1080p and downconvert later. Shoot 720p for slow motion and for scenes where you want to capture high speed motion. Otherwise shoot 1080p. To achieve 60p in 720 the camera is shooting at exactly half vertical resolution, so it isn't downconverting from 1080p to get 720p it is converting to 1280x720 from 1920x540.

I think that a final SD product will always look better when starting from the high resolution possible.

Great answer Andy. Particularly on how the imager shoots the 720 60p. I never realized that. I wish they made it a little quicker to jump between formats and speeds in the menus when you are seriously under the gun though.

[Tim Polster]

[QUOTE=Andy Shipsides;1155414]IMHO you should always shoot 1080p and downconvert later. /QUOTE]

While we can all agree more resolution is great, but the word always is a bit strong in this context.

What if the project looks best with the smooth motion of 60p?

1080i and 1080p are not the same thing. I prefer to shoot 720p60 over 1080i for the progressive frame handling if the slower framerates do not match the project style.

[David Heath]

Originally Posted by Andy Shipsides

To achieve 60p in 720 the camera is shooting at exactly half vertical resolution, so it isn't downconverting from 1080p to get 720p it is converting to 1280x720 from 1920x540.

I think you may be confusing cameras, Andy, if you're referring to the EX?

The best tests I've seen on the EX are from the BBC R&D department - see http://downloads.bbc.co.uk/rd/pubs/w...X1-and-EX3.pdf .

Most relevant to this discussion are the zone plates and discussion on page 16, and it becomes clear that the 720p must be derived from 1920x1080, not 1920x540, as the vertical resolution is well over 540 AFTER downconversion.

Vertically, things are a little better, there is a smooth progression into extinction at 680 and virtually no aliasing. Therefore, the downconversion appears to be a little asymmetric, but in an acceptable way.

It's also worth noting what the BBC say about deriving SD from the EX:

There is no standard definition recording mode in the EX1. However, it records at 1280x720p in HQ mode (35Mb/s), and this mode is interesting because it represents the best way to get a standard definition picture from the camera. If recordings are made at 1080 interlaced, then the down-converter (external) will have to de-interlace in order to produce the output fields, while recording at 1080 progressive may not give the look the user wants (jerky motion). .............

and.........

Clearly, a subsequent down-conversion to standard definition from this format should be the best route to take. It is highly unusual to see such good downconversion in a camcorder.