www.ssontech.com

[cupoftea]

Hi,

pretty new to syntheyes, only been looking at it for a couple of months. I have been shooting some shots in my house just to get used to the software and practice a bit, as I have a project starting in the next couple of weeks at work for which I'll be using syntheyes to get camera solutions for some 3d and 2d inserts.

My question is... I have been shooting on a sony DCR VX200E, it's a pretty old pro-sumer camera, but after doing a few tracks on some interlaced footage I was pleasantly surprised to find out that it will shoot in progressive scan mode...

I did a quick shot of the coffee table and captured the video, imported it in to syntheyes with interlacing set to 'no' and then became incredibly disappointed; with the shot in SE I noticed that I have what seems to be a 24 fps sequence with every second frame as a repetition of the previous one; ie frame 1 and 2 are the same, frame 3 and 4 are the same, frame 5 and 6 are the same and so on.

besides the fact that this makes for a jerky 12fps video, it also seems to put a spanner in the works for syntheyes in that it is trying to extrapolate an expected movement on every second frame when in fact there isn't one (just a repeat of the previous frame and therefore the previous feature position).

So, my questions are... firstly does anyone know if this is common in low end progressive scan implementation in camcorders (is it 'psf'?) or if it isn't, then am I doing something dumb with the camera settings when shooting?. I don't want to go back to shooting interlaced footage as the images I get from 'progressive scan mode' are much crisper, and easier to work with (or rather, would be easier to work with if there where twice as many).

can anyone help me get the best out of this fairly low-fi set-up?


on a related note the camera I'l be using at work is a sony DSR-PD 170p, although I think it's pretty much the same generation as the vx200 so wll probably have the same progressive scan implimentation, does anyone have any experience with this camera to confirm or deny this suspicion

Apologies for the long winded question, probably haven't explained it that well either...

[kenekeu]

I had the same thing happen on an HVX200 using the 3:2 pulldown to 24 FPS. If you are going to use progressive footage you need to have true progressive footage not a pulled down simulation of progressive footage. I had to use Shake to eliminate the duplicate frames then everything went perfectly.

I doubt if a low end camera can shoot pure 30P so you are going to have to use Quicktime or some video editing application to deinterlace to true 30P. I don't know too much about your camera so I'm not sure exactly what to tell you. Check the manufacturer's website for specifications and also check the discussion forums on the manufacturer's site for clues. Good luck.

[ssontech]

NOTE: these kinds of patterns are extremely common as the data recorded to tape must meet a specific 29.97 frame rate to be at spec. So if the source is 24fps then a repeat pattern is needed. This pattern is different than an interlace, because there is no loss of data or resolution involved. It is just a coding gimmick to meet the existing standards. So you can use a variety of tools to pull it back out, for example Final Cut has one. You want to do this pretty much no matter what you are doing, not just SynthEyes, to recover the original as-shot frames.

Bonus tip: the standard tape frame rate is 29.97 by decree, right? The repeat pattern, of whatever flavor, increases the frame rate by 5/4, so removing it chops the frame rate by 4/5. To make the numbers work out nice, and avoid having to do anything trickier, typically the "24 fps" footage is really 23.976 fps === 29.97 * 4 / 5. You need to be really sure you get the 23.976 part right everywhere or you can wind up with some very subtle duplicate/dropped frames and sound sync problems. Some older software may not accommodate a 3-fractional-digit frame rate at all---if you call it 23.98 you're still going to have some problems on long shots. You've been warned.