24p conversion: What source should I use? 30i vs 30p

[kakomu]

Hello all:

When I record with my MiniDV camcorder (Canon Optura 50, NTSC), I tend to set the camcorder to TV mode (shutter priority). I tend to shoot in either 30 or 60. When I shoot in TV 30, I get 30p with no interlacing and a decent amount of blur. When I set it to TV 60, I get 30i.

What I'm wondering is, in which mode should I shoot if I plan on doing a conversion to 24p? I know that if I shoot in 30i, I can easily convert the video to 60p with a bobber and then to 120p and decimate to 24p. On the other hand, mvflowfps did a pretty good job of converting a 30p clip I made into 24p. The motion blur in my 30p source clips look better than the motion blur in my 30i source clips.

I can also maintain a full frame when I shoot at 30p, but I'll have to go with a half frame with 30i.

So, which source would be better for 24p conversion?

[Guest]

Use the one that produces results that you find preferable.

BTW, there's no need to go up to 120fps with your bobbed stream.

[Blue_MiSfit]

Indeed. It really depends on how your camera creates 30p internally. It will either scan its senor progressively (ideal), or it will just do a bad deinterlace (likely)

I would try shooting a repeatable scenario with the camera in both 60i and 30p modes, and compare the results of using a decent bobber + mvflowfps versus the camera's progressive output + mvflowfps.

Decimation could be used as well, but flowfps will probably look a lot better (at the risk of some motion artifacts)

~MiSfit

[2Bdecided]

I think it's a matter of reducing the mvflowfps artefacts. It's quite noticably horrible when it goes wrong - and it will go wrong!

If you are going up to 120fps with mvflowfps, you can add some motion blur with a simple temporal soften before decimating. This can be very useful for 24p if the original shutter speed was faster than 1/48.

Cheers,
David.

P.S. I've done this already...
http://www.hv20.com/showthread.php?t=2876&highlight=format
...but the clips have expired. The still are still available to view though.

[WorBry]

When I shoot in TV 30, I get 30p with no interlacing and a decent amount of blur. When I set it to TV 60, I get 30i.

Interesting. Are you sure you are actually getting 30p? I was under the impression that the Optura 50 only offers interlaced recording (60i, or 30i as you call it). Had a look at an on-line manual and some reviews and cant find any mention of a (pseudo) progressive or frame mode. The Tv-30 and Tv-60 settings you refer to are actually the adjustable shutter speeds in Tv (Shutter Priority) mode, are they not?

At 1/30 sec shutter speed, it would seem natural that the motion difference between consecutive fields captured at 1/60 sec intervals will appear in the composite 60i frame as blur rather than the discrete interlace lines (mice teeth) apparent at 1/60 sec shutter and above. This is explained by the fact that at shutter speeds lower than 1/60 sec a camcorder CCD does not completely discharge, allowing pixel charges to spill over from one recording cycle to the next (hence blur), wheras at higher shutter speeds the CCD is forced to completely discharge between cycles.

I guess there is a possibility that the camera is performing some internal deinterlacing - at worst discarding alternate fields. However, if it were true 'frame mode' recording, where the normal CCD timing is offset to capture both fields at the same instant, I'm sure Canon would have described it as such, and typically there would be some loss in vertical resolution, and likely aliasing artifacts.

If you are happy with the overall 'look' (degree) of the 'Tv-30 mode' blur (at the expense of losing fast motion detail), why even bother converting to 24p?

[kakomu]

Well, after taking a much closer look at the resultant raw images of TV30 vs TV60, I cannot say for certain what is going on. I do know that at 30fps, no combing exists, but I can't say for certain if that's because the fields are blended or it's an actual progressive frame. I guess the euphoria of having discovered some totally awesome blinded me.

[IanB]

@kakomu,

Well I guess you need to do some testing.

Mount the camera on a tripod. Shoot a static scene in both mode, something with fine detail, like a newspaper. Shoot a moving scene in both mode. Ideally smoothly pan the camera at a reasonable rate, again with a scene with plenty of fine detail plus some vertical, horizontal and angled sharp edges, i.e. poles and wires make good test material.

Then critically examine all the footage.

[2Bdecided]

The Canon HV20 and HV30 camcorders will do a "fake" 30p (60i) or 25p mode (50i) if you reduce the shutter speed sufficiently, which sounds just like the camera described here. This is visibly different from the real progressive modes available on the HV20 and HV30; when using the shutter speed trick in interlaced mode the data seems to be taken from a single field and expanded to fill the frame.

The results aren't that bad really.

http://www.hv20.com/showpost.php?p=54055&postcount=42

"discussion" which reveal most people can't see the difference (though remember this is HD)...
http://www.hv20.com/showthread.php?t=6604&highlight=field&page=4

Cheers,
David.

[WorBry]

Had a look at my old(ish) back-up Sony DCR-PC115E (PAL DV) camcorder and lo and behold, tucked away in the Digital Effects menu is a Slow Shutter option with 4 possible shutter speeds - 1/25, 1/12, 1/6, 1/3 sec.

Tried the 1/25 setting and guess what - no interlace combing. Not bad on a tripod with moderate subject movement, but for hand-held shots, way too much blur, even on slow pans, for my liking, not to mention an appreciable degree of edge aliasing.

Again, this begs the question, is the camera performing some internal deinterlace/single field trickery or is it simply the natural result of capturing consecutive interlace fields in the normal way (every 1/50 sec) within a 1/25 sec exposure window.....in the manner I eluded to above (for a 60i NTSC cam, that is).

Again, there is no mention in the manual of this being a special 'progressive', 'movie' or 'frame mode'. The stated use is for 'recording dark pictures more brightly', which I guess it does, albeit with an appreciable amount of noise. Certainly doesnt come close to the pseudo-progressive Frame (Procinema) Mode on my Pana NV-GS400.

Couldnt see myself using it for general, hand-held, home video recording (I rarely use a tripod and always carry a good video light). I'd go with 'normal' (1/50 sec shutter) 50i recording any time. Went through a 'film look' phase myself - deinterlacing (MVBob/MCBob) to 50p and then decimating to 25p with motion blur (using mvfps and similar temporal super-sampling/blur routines). Was never entirely happy with the results - always some structural distortion with the available mo-comp interpolation tools. Nowadays I prefer to keep at 50p (XviD and x264) for PC viewing.