Stop motion swing analysis

[Don Palomaki]

Mark Rosen posted a comemnt on using 30p vs 60i to do stop motion analysis of a bat swing. Because the thread is closed, and a quick search did not turn up anything obvious on video for swing analysis:

I would think that 60i (with high shutter speed to reduce motion blur) will provide a more useful result because you will have twice as many samples (one every 1/60 rather than one evey 1/30) to look at. This is especially valuable for fast motion events such as a bat or golf swing. And you may find that even a field every 1/60 may not be enough sample per swing.

As I understand it, at contact with the ball a bat is moving pretty fast, maybe around 90 feet/second depending on the player level. At 30 samples per second (30P) you would likely miss a lot of the swing, and 60i, while lower vertical resolution due to interlace, may prove more useful overall as you work with 2x am many individual fields rather than full frames.

[Stefan Scherperel]

I agree. If it were for analysis, 60i, deinterlaced to 720P 60 would give you more temporal resolution.

[Mark Rosen]

Don,

Thanks for keeping my post alive. I tried a search on the subject but did not really find anything. I do not understand why my post was closed, whatever.

Anyway I wanted to mention that I believe Canon's own broshures talks about how their 30F mode is ideally suited for sports as every frame is captured clearly and independently. I do not think shooting in interlace 60i mode really adds additional frames but rather divides each frame in two. This allows analog TV to draw the picture with the gun making two passes for each frame.

I may be misunderstanding this. I learned that the XH A1 chip set is interlaced and therefore the camera still captures in interlace, but then does an internal interpolation and then spits out 30F. I was just interested as to the quality of this proccess verses true Progressive capture as in the XL2.

Thanks,


Mark

[Dave Mody]

I profess to be confused by that last post. Here's how I understand it...

A chip that's 60i means it will capture 60 fields per second. That's the key.

HDV 60i will be laid down on the tape as 2 fields per frame. Thus 60 fields per second. No muss, no fuss.

30F will require that the interlaced fields be mathmatically combined to form a single frame. Some sort of a frame blending algorithm (called deinterlacing) is applied to the two interlaced fields and voila, a single frame is magically created and put onto the tape. The generated frame is never going to 'stop' the action as effectively as the raw data in the fields, it just may look more clear.

[Mikko Lopponen]

Originally Posted by Mark Rosen

I do not think shooting in interlace 60i mode really adds additional frames but rather divides each frame in two. This allows analog TV to draw the picture with the gun making two passes for each frame.

I may be misunderstanding this. k

Well you are. 60i is 60 fields per second. That is 1440x540 at 60 fps.

30p is 1440x1080 frames per second.

[Mikko Lopponen]

Originally Posted by Dave Mody

Some sort of a frame blending algorithm (called deinterlacing) is applied to the two interlaced fields and voila, a single frame is magically created and put onto the tape. The generated frame is never going to 'stop' the action as effectively as the raw data in the fields, it just may look more clear.

It's not magic and it's just as "stopped" as the interlaced frame. If you want clear then just up the shutter speed.

[Don Palomaki]

Mark.
Try both methods (60i and 30p) and see which gives the result closest to what you seek

For relatively slow action ( a peson sprinting at 10 mph (for example, such as instant replay of a tag, 30 fps is probably adequate for most purposes.)

Don

[Stefan Scherperel]

I think people are way overanalyzing this whole thing.

60i = image sampled 60x per second

30P = image sampled 30x per second

etc.

now granted 60i when deinterlaced to 60p will be lower resolution than 30p, 1080 60i deinterlaced to 720 60P looks phenominal. Just remember that if your intent is to slow this footage down and analyze frame by frame 720 60p will give you twice as many frames as 1080 30p. Also remember to shoot with a minimum os 1/120th sec shutter speed, you could go higher on this if you want no motion blur on the club as you are swinging.

[Bogdan Tyburczy]

The most important trick here for great looking slow-mo out of 60i or 50i is fields->frames conversion. Barlow Elton has posted some nice example in this thread:

http://www.dvinfo.net/conf/showthread.php?t=75384

Video clip may not be available, but description of the method is there.

[Mark Rosen]

Thanks Don and everyone who posted with their help.

I have been doing a bit of research over the past couple of days regarding slomo techniques. I currently have PP 1.5, CS2 and Encore 2.0 etc.

I do not have After Effects. Here are my questions:

The sample slomo clip of people with shopping carts that Barlow Elton posted. Was that completely done within A/E and no third party plug in such as Twixtor? If so, pretty darn impressive.

I am ready to make the purchase of A/E 7.0. I noticed that there is a pro version for $999.00 and a standard for $699.00.
Does the standard version have all the needed tools, (i.e frame doubling or intopolation needed to convert 60 fields to 60 frames P) to do the quality slomo of Barlow Elton's clip? Or do I need the Pro version of A/E?

With A/E is threre any reason that would prevent me from being able to import my slomo back into PP and then output to DVD?

Lastly, I see there is a plug in for Twixtor for Premiere Pro. Would I be better off getting this plug in in terms of slomo quality?

I realize that I did not provide the link for the clip, I will try to find it now.


Thank,

Mark

[Greg Boston]

Just to add to this thread a bit. I agree that 60i or 60P for that matter, is going to be marginal for registering the swing of a bat or golf club clearly at impact. I am experimenting with 60P overcrank on my F350 for the purpose of recording and analyzing golf swings. For best results, get as much light as you can and use a high shutter speed (1/500 or faster) and stop down for deeper DOF if shooting from in front of or behind the person doing the swinging.

Oddly enough, my little Panasonic 953 has a feature for swing analysis that grabs a number of frames but increases the sampling rate to a higher number towards the end of the interval to more precisely capture impact.

Here's some golf info for you to crunch on. Most tour players have a club head speed at impact of 120mph to 130mph. That should allow you to calculate how fast you want the shutter speed in order to freeze that motion.

While you can freeze the individual frames, it's getting enough frames within a second that's the hard part.

-gb-