Why lower field first vs. progressive?

Shredder wrote on 8/19/2002, 11:19 AM
Hi,

Is there any benefit to render lower field first instead of progressive? I'd like to render progressive so I can eventually burn my files to DVD.

If I play a progressive file on a non-progressive device, like VHS or even regular TV, is the quality degraded compared to LFF, or is it the same in that case?

LFF is clearly lower quality if displayed on a progressive device.

I guess here's my thinking: Some of my source files are LFF, but my titles, effects etc. would benefit from progressive rendering. I'd like to get as much qulaity as I can.

Finally, since I'm trying to understand, in LFF, you have 29.97fps, is each frame 720x480, or just 1 field (so 360x480 pixels of data). -- Does progressive result in double the visible pixels per frame, resulting in twice the quality?

I haven't been able to get a straight answer on this.

Thanks,

Jon

Comments

Chienworks wrote on 8/19/2002, 11:48 AM
In response to the last, the fields are made up of every other scan line, so a field is 720x240. Two fields are interlaced together to produce the full 720x480 frame. The problem is that the two fields are also 1/60 second apart in time so that combining them into a single progressive frame can lead to the combing effects that you see during rapid motion (lines 1, 3, 5, 7 ... etc. come from an image that happened 1/60 second AFTER lines 0, 2, 4, 6 ... etc.).
Cheesehole wrote on 8/20/2002, 2:12 AM
you should probably read into this some more because you don't have to render to progressive for DVD's, but it's still a good idea for a lot of stuff. this article gave me a really good education on these matters. since you are thinking about DVD's this is especially relevant.

http://www.hometheaterhifi.com/volume_7_4/dvd-benchmark-part-5-progressive-10-2000.html

I don't think there is ever a need to render to interlaced for DVD or DV unless you have a special reason to (if all your source material is interlaced you may as well keep it that way).

personally, I shoot and render to progressive for just about everything. (if I'm shooting specifically for smooth slo-mo, then I'll shoot Interlaced to get 60 samples of time per second instead of only 30) interlace technology and the combing artifacts is something I like to avoid when possible.
DougHamm wrote on 8/20/2002, 12:43 PM
One simple answer: If you are doing generated text rolls, transitions, PIP movement, pan/crop, etc. on footage meant for TV output and you want the rendered output to move smoothly (60 fields per second) you should render interlaced. Otherwise stuff that was interlaced will remain so, but newly generated movement will be progressive, giving you an odd mix of smooth and stuttery movement.

-Doug
Cheesehole wrote on 8/20/2002, 9:30 PM
I wouldn't say stuttery, but yeah that's a good point Doug. if you are outputting for TV you'll want to match your interlaced 'source footage' with interlaced 'generated footage' (moving stills, overlayed graphics, etc...) so everything has the same sort of liquid smooth 60i motion.
DougHamm wrote on 8/20/2002, 10:52 PM
Yeah, I used 'stuttery' for lack of a better word. It certainly isn't 'jerky' like some would say. Perhaps 'staccato'? :)

I've actually used progressive mode for some things I've done, like a half-hour promo video for the Stroke Recovery Association of Manitoba I did last year. It lends a certain overall feel to the right kind of material. I own an original Canon Optura, the only camera I know of that has ever featured a full resolution 30fps progressive CCD. Low light sensitivity and battery life weren't foremost in the design plan, but otherwise this camera was and still is a wonderful little tool!

-Doug