Isnt 60I the same as 29.97?

[MagicCat]

HI All

After ten years, I thought I understood the differences in the new and old formats. Maybe I need to forget my entire career and learn over:

I just read a tutorial ( http://eugenia.gnomefiles.org/2009/02/09/butter-smooth-slow-motion/ )of how to get smooth slow motion through a variety of processes. The person that authored the particular tutorial I was looking at, suggested that to make his process most effective, the camera needs to be setup to shoot in the "Highest frame rate possible" and suggested 50 or 60I. (The Tutorial was geared towards AVCHD Cams but seemed to imply it would work well for even for my HVX footage, if shot in a 60i mode)

Why are people referring to 60i as a faster frame rate than 30p or 29.97???? Isnt 60I just the politically correct way of calling 30fps video, ( AKA: 29.97) Interlaced?

I understand 30p and 24p Video, and understand over-undercranking completely. I use it all the time from 2fps to 60. But someone suggesting that 60i is a way of overcranking threw me for a loop?!?. Maybe it has something to do with GOP Codec video like HDV, AVC or XDCamEX.

It should be noted that I also have a friend with an HMC150 and he also talks about using 60I for Slow-mo? Maybe there is something to this???

Someone please eduacate me on what Im missing here. Im all Befuddled now.:huh:

MagicCat

[Barry_Green]

60i = 60 motion samples per second.

30p = 30 motion samples per second.

29.97i = an immensely irritating and confusing naming system that serves no purpose but to muddy up the discussion.

29.97i = 60i
29.97p = 30p

29.97i looks nothing like 29.97p. So let's just dispense with the "29.97i" terminology once and for all! :) Camcorder manufacturers are pretty much universal in referring to 60i as 60i, 50i as 50i; I don't think any camera manufacturers are using "29.97i" terminology. Avid still does.

[MagicCat]

Yeah, lets leave the 29 behind.

Do Samples Equal actual "Frames acquired per-second" or is the camera actually "scanning" a single frame twice at 60i, for better, smoother, more newsy-looking (smoothness of interlaced) playback/re-production.

In short, I would think if something is being sampled, there are 30 extra frames in there somewhere when shooting at 60i.

Color me stupid Barry, I'm still slightly confuddled.

[Barry_Green]

Let's take the example of 1080/60i. It could be called (confusingly) 1080/29.97i. But what it really is, is 540/60p. There are 60 scans every second, each one of 540 lines (a "field"). There is no such thing as a "frame" of 60i, there are instead groupings of even and odd field pairs, but they don't actually form a "frame" since they're sampled at different points in time.

So really, it's 540/60p. Half the vertical resolution, scanned at 60 frames per second. The system alternates between scanning even lines or odd lines, but other than that, you really can think of it as 540/60p and it'll make the whole thing a whole lot easier to understand.

[MagicCat]

Thanks for that Barry. Yes, that is what I thought to begin with. That was a VERY good/accurate way to present it too!! 540i or in the case of DV, it would be 240i. Interesting!!

What I don't understand is how one could claim to get slow motion by converting it to 30p??. That makes no sense to me at all?. If you de-interlace something that was 60i, it is still 30 frames a second no matter how you cut it. For that matter, DV, or something shot on lets say, a VX1000 is inherently interlaced Video. De-interlacing it exporting as progressive scan will not make it run at half speed.

Unless Im just not understanding it right, the Tutorial I wrote about in the beginning of this thread, stated to shoot in 60i, kind of suggesting that there were more frames to break down, to provide better slow motion. It is true that interlaced video looks much smoother than Progressive scan, and I suppose that is because it is sampling more fluidly so there arent any abrupt, or at least "perceptible" breaks between frames. when converted to progressive scan properly. Maybe that is what they are getting at??

[Barry_Green]

If you de-interlace something that was 60i, it is still 30 frames a second no matter how you cut it.No, if you de-interlace 60i, you get low-res 60p. De-interlacing means making one frame out of a half-resolution field. You have 60 fields, so they can become 60 frames. Low-res frames, but frames nonetheless.

So, yes, if you shoot 24p you have 24 motion samples per second (using full frame progressive imagery). If you shoot 60i you have 60 motion samples per second (but only half-resolution "fields".) If you slow down that 60i to play back at 40% speed, and de-interlace each field to become a full frame, then you have perfectly rendered 60fps slow motion. It's just low-res slow motion.

[Damodt]

Sorry to jump in here, but this is interesting. So shooting at 30p overcranked to 60 give the best slo-mo on the HPX?

[Barry_Green]

On an HPX170, HPX300, or HPX500, you have variable frame rates to choose from in the 720p mode. So choose 24pN, 25pN, or 30pN, whichever you prefer, and then choose the frame rate you want based on how slow you want the slow-mo to go. 48fps in a 24pN project = 2:1 slow mo, same as 60fps in a 30pN project or 50fps in a 25pN project. 36fps = 1.5:1 slow-mo in a 24pN project. Yes, all these techniques will result in full-resolution, crystal-clear, perfect slow-mo from an AG-HPX series camcorder.

Be sure to set your shutter to the syncro scan shutter, and choose a shutter angle between 150 to 220 degrees, usually around 180 to 200 degrees.

[Damodt]

:thumbup::dankk2:

[MagicCat]

No, if you de-interlace 60i, you get low-res 60p. De-interlacing means making one frame out of a half-resolution field. You have 60 fields, so they can become 60 frames. Low-res frames, but frames nonetheless.

Interesting. As always, you are a Font of Knowledge and the supreme simplifier of all things technical to the vidiot peasantry Barry!! I had always thought that De-Interlacing was essentially the process of taking all 60 fields and flattening them into a single frame, Hence, my statement that "no matter how you cut it, you end up at 30fps" Alas!! my lightbulbeth turneth on-eth. (boy do I feel stupid, after all, when you de-interlace, you have to make a choice of upper or lower. DUH?!) That also completely makes sense why interlaced appears so fluid.

With this in mind, is the process of de-interlacing by interpolation, be the process of combining both fields to make one frame? Or have I just requested a whole other topic.

You need to Change your name to Barry Not-So Green :thumbsup::thumbsup::thumbsup:

[Barry_Green]

"interpolation" usually means using one field and up-rezzing it from 540p to 1080p, doubling its vertical size and "interpolating" (i.e., "guessing") the missing information.

The other way to de-interlace is to "blend fields" where it takes two or more adjacent fields and tries to guess what should go between the current fields' lines, compensating out for motion etc. For accurate slow-mo you'd want to use "interpolate".