Converting 720p to 720 interlaced???

[Bill Edmunds]

I was reading through the HD100 brochure and came across this: "the progressive signal can be easily converted to interlaced." Ummm... how? I know Final Cut can deinterlace footage, but how do you "interlace" progressive footage?

[Stephan Ahonen]

You just take each progressive frame and eliminate either the even or odd lines. You would do this for NTSC 30i broadcast of 720p material, scaling the progressive frames down to 480p before interlacing them. It's far easier than 1080i->480i downconversion, which I suspect is why most broadcast networks chose 720p as their HD standard instead of 1080i.

[Bill Edmunds]

Originally Posted by Stephan Ahonen

You just take each progressive frame and eliminate either the even or odd lines. You would do this for NTSC 30i broadcast of 720p material, scaling the progressive frames down to 480p before interlacing them. It's far easier than 1080i->480i downconversion, which I suspect is why most broadcast networks chose 720p as their HD standard instead of 1080i.

If you don't scale it down to 480p before interlacing, what do you wind up with? 720i? How would you do it in an NLE?

[Stephan Ahonen]

There is no interlaced 720-line standard, so you would never need to do it. The only way a 720-line image will ever be interlaced is if it's cross-converted to 1080i or downconverted to 480i. What the brochure is referring to is that a progressive signal is more easily converted to an interlaced standard than an interlaced signal can be converted to a different interlaced standard or a progressive standard.

I suspect any decent NLE would automagically handle interlacing the footage if you ever dropped a progressive clip into a timeline that was using an interlaced standard.

[Marijn Schuurmans]

Hello,

I thought you have to shoot your footage at twice the frame rate before you can turn it into fields. I can choose an option in the timeline "interlace consecutive frames" but you keep half your f/s (because 2 fields are 1 frame).
So if i want to turn 25p progressive material into interlace and just export a movie at 50i I see no difference.

[Stephan Ahonen]

That's correct, 25p can't magically turn into 50i because the temporal resolution isn't there in the first place. You have to shoot 50p.

[Nima Taheri]

How about turning 50p into 25p? How does the NLEs/converters do the pulldown/conversion?

Will 50p footage converted to 25p have the exact same look as if it was shot in 25p?

[Ken Hodson]

Sure you can turn 25p into 50i. It doesn't suddenly gain temporal motion, but will look just like the 25p material, except on an interlaced TV. Just like watching a movie on your TV. Films are shot at 24fps and watched on your 50i/60i TV. No need to shoot 50/60p if you need to interlace, that is just silly.

[Stephan Ahonen]

Originally Posted by Ken Hodson

No need to shoot 50/60p if you need to interlace, that is just silly.

There certainly is a need for it if you want it to look like native 50/60i material, and that's what I'm talking about here. The ability to pull down frames really goes without saying.

[Werner Wesp]

Quite right, if you want all the 'advantages' of interlaced (i.e. smoothness) you'd need to shoot in 50p.

What is actually meant by the phrase that is is easy to convert should be read as: "you can save your progressive video as an interlaced one without loosing to much quality" - of course you won't gain any smoothness that is there with the interlaced originated footage - the data in 2 fields will be of 1 image, taken at 1 point in time (instead of 2 fields for 2 moments in time as is the case with original interlaced footage).

It is especially easy if you compare it to the conversion of interlaced in progressive. There you'll loose quite some of your image quality (in the worst way you'll cut your vertical resolution in half. Obviously there are better ways, but there's always some strain on the original image quality).

How about turning 50p into 25p? That depends on the method you'll be using. You can show 2 frames at once with 50% opacity, creating (more or less) the same effect as the 'motion smoothing filter' in the JVC cam or you can choose to show just 1 of the 2 frames originally recorded. In that way you'll have the same as what's shot in 25p. The only thing that xould be different in the last one is that you might have shot it with a shutter of 100 in stead of 50, so after converting it to 25p, it'll look like 25p shot whit shutter 100, instead of the more 'normal' look of 25p shot with shutter 50...

[Ken Hodson]

I didn't understand the nature of the discussion of getting the footage to look like it was shot on an interlaced cam, but simply converting to interlaced. There still is no need to shoot at a high frame rate in my opinion, just shoot properly in the first place. Like any of the millions of film that we watch on our TV's.

[Stephan Ahonen]

Originally Posted by Ken Hodson

There still is no need to shoot at a high frame rate in my opinion, just shoot properly in the first place. Like any of the millions of film that we watch on our TV's.

You're making the rather large assumption that everything we shoot will lend itself naturally to slow and controlled camera moves and subject motion. Remember that this is an ENG camera as well and it's not limited to shooting indie films and interviews, but also fast-moving unpredictable events in the field. Also bear in mind that HDxxx footage may be required to cut seamlessly with other interlaced or high frame rate progressive footage, especially in a broadcast setting. I've seen someone try to cut an interview shot on an HD100 in 30p into a 60i SD broadcast and it simply looked bad. Even with a fairly stationary subject the lower temporal resolution was clearly visible.

[Ken Hodson]

Originally Posted by Stephan Ahonen

You're making the rather large assumption that everything we shoot will lend itself naturally to slow and controlled camera moves and subject motion. Remember that this is an ENG camera as well and it's not limited to shooting indie films and interviews, but also fast-moving unpredictable events in the field. Also bear in mind that HDxxx footage may be required to cut seamlessly with other interlaced or high frame rate progressive footage, especially in a broadcast setting. I've seen someone try to cut an interview shot on an HD100 in 30p into a 60i SD broadcast and it simply looked bad. Even with a fairly stationary subject the lower temporal resolution was clearly visible.

If you can't shoot properly, don't shoot with a progressive cam. I have seen more then a few interview type films shot at a mere 24fps film never mind 30fps and of course they look fantastic. How odd. Hmmm. Of course if you must shoot in an ENG fashion, with random cam swings and simply in a way that suits interlaced video there is always the 50p/60p SD mode to fall back on. Otherwise don't use a progressive cam. I have shot lots of interviews in 30p and I simply don't have a clue as to why you say it looks inferior. It simply looks filmic instead of video-ish. If your interview is temporal resolution limited, I would simply have to ask, what the hell is the interview subject doing?

[Werner Wesp]

I have to agree to both of you. No matter how fast the action is, you can shoot it and make it look great in 25p or 30p. Even shot from the shoulder ENG-style. Once, I've made a 2 minute clip of some badminton just to show that, for those that didn't believe 25p could be smooth. You need to be able to handle the cam, but with the rules in mind and some dedication to your work it's fine, even in ENG circumstances.

On the other hand Stephan has a point when he says it's visible when you intercut it with 50i or 60i. That is quite true as well. You'll spot that a mile away.

[Marijn Schuurmans]

I've shot a videoclip in Pal 25p. Now they want to broadcast it interlaced from a DVCam recorder. Will I loose resolution?
Thanx.