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Brendan Maghran
light streaks
on Nov 2, 2009 at 3:16:03 am

I'm shooting a music video for a pop band soon and want to be able to make it appear as though light streaks are coming out of the drum sticks and guitar as they move. I know about the After Effects light streaks tutorial on video copilot, I was wondering if there is a way that would look authentic in motion. I have tried using the painting streaks.


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david bogie
Re: light streaks
on Nov 2, 2009 at 10:27:01 pm

Kind of depends on the effect you want. In AE, I'd either mask the sticks and put the effect behind the mask or I'd shoot it with retroreflecting tape on the sticks and a light on the camera to give Motion or AE a solid target to create superb tracking for additional emissions systems or alpha amsks for light streak filters.

If you haven't shot it yet, get some retroreflection tape. You may need to shoot your drummer with twice the light and half the shutter speed, at least 125/second. Can you rent a higher frame rate camera? Say, 60fps or 90?

bogiesan



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Brendan Maghran
Re: light streaks
on Nov 3, 2009 at 12:42:26 am


If I put reflective tape on the sticks how well can motion track it? I've never used the tracker in it. In terms of renting a higher speed camera, I'm doing this at school, so I really can't. The song is a dance club type of song, and the band is going for a very colorful image. I want neon light streaks to look like they're coming from the drumsticks and guitar as they move.

After using the tracker in motion or AE how would I connect the tracker to the light streak effect? I'm pretty amateur in AE, but little better in motion so some of this stuff is relatively new. Any help is very, very appreciated.

And when you say you'd mask the sticks do you mean you'd rotoscope the sticks? Sorry if I sound confused.

Thanks,

Brendan


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david bogie
Re: light streaks
on Nov 3, 2009 at 3:30:17 pm

[Brendan Maghran] "If I put reflective tape on the sticks how well can motion track it? I've never used the tracker in it. In terms of renting a higher speed camera, I'm doing this at school, so I really can't. The song is a dance club type of song, and the band is going for a very colorful image. I want neon light streaks to look like they're coming from the drumsticks and guitar as they move.

Tracking depends on clarity of the image, the pixels must be easily discerned by the software. That requires contrast or distinct hue differences. Drum sticks are moving really fast so they appear blurred if shooting at 1/30 or 1/60 second. You must figure out a way to freeze them by shooting with more frames per second, faster shutter speeds like 1/250 (which demands MUCH more light), or you simply cope with the problems caused by your limited gear and skills. But you cannot blame After Effects or Motion for their shortcomings if you are unable to supply minimum image quality required for basic tracking.

[Brendan Maghran] After using the tracker in motion or AE how would I connect the tracker to the light streak effect? I'm pretty amateur in AE, but little better in motion so some of this stuff is relatively new. Any help is very, very appreciated.

Using the Trackers in AE or Motion is not easy but you're not alone. Open the manuals, find some online tutorials and prepare yourself for several practice sessions. You will quickly realize tracking for image stabilization is different form tracking for the application of effects. You will quickly realize how fragile the tacking systems are and you will be totally confused by the endless options in the tracker controls. Once your video has been successfully analyzed, you will "simply" apply the tracking information to the effects controls. Not difficult. The hard part is manually correcting all of the frames where the tracking slips.

Mocha is a comprehensive tracking tool supplied with AE. I have never opened it.

[Brendan Maghran] And when you say you'd mask the sticks do you mean you'd rotoscope the sticks? Sorry if I sound confused. "

Reflective media will create a distinct hot spot in your video and that can easily be luma keyed IF YOU UNDERSTAND LIGHTING FOR VIDEO. Your set will have a different lighting ration than your on-camer alight. If you have no control over the set's lighting, you're screwed anyway. You could use an intense blue light on the camera and use a simple chromakey to pull the mattes from the sticks. But these are effects based on the assumption that adjacent pixels have unique values and your sticks are going to be all blurry unless you figure out a way to freeze them. If you cannot apply an automated matte, you must rotoscope them. Up for that? i don't think so.

bogiesan



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Brendan Maghran
Re: light streaks
on Nov 3, 2009 at 4:37:10 pm

Well in terms of control over the set, I have complete control with a whole ceiling grid of lights and a couple ARRI kits at my disposal, so lighting is not a problem in terms of amount. I'm not entirely sure if I can shoot at 90 fps but will look into it for sure. Do you think that shooting at 1/125 would help the camera recognize the reflective tape easier with less blur?

Today I practiced in motion with the trackers, the transformation and 4-point behaviors. I was able to track an object fairly well, but I don't know how to connect a particle emitter or replicator to the tracked object.

I understand the hot spots in video and I can definitely Luma key them out, but I don't really understand what you mean with using a blue light on the camera and pulling the mattes from the sticks, what would pulling the mattes from the sticks do, could you elaborate on that?

I don't really work in any sort of special effects programs very often, I spend my time studying editing and using FCP and Avid, so thanks for helping me out it's much appreciated.


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david bogie
Re: light streaks
on Nov 4, 2009 at 3:23:51 pm

Excellent.
A blue camera light will allow you to use the chromakeyer on the retro tape, a simple and direct method of pulling a matte. "To pull a matte" is a generic term, unfortunately, it means several different things. In this case, when you process the video of the sticks—using any of the methods we've discussed—you end up with drumstick-shaped holes on the alpha channel, these are the mattes. You have successfully pulled a matte if it is useful in the next steps.

Once you have the holes, you can use them as the sources for light streak effects. But the holes themselves, the matte video track, are much more useful. If you export the holes as a self-contained movie, you can easily track them since the movie is binary, black and white. This tracking information can be used to feed the position parameters of your emitters. You're on your own figuring that out, it's all in the manual, not very difficult. You want to read up on Track Parameter Behavior.

You can also place small tracking dots on the sticks during shooting, something that will be easily recognized by your tracker. They could be retroreflective tape or they could be red if your background is blue or green. Trackers can be programmed to search for and track hue or luma differences.

Shooting at greater than 60fps is probably not possible with your camera. 90fps will give you nice slow motion of a drummer. 120fps will give you languid slow motion.
A fast shutter speed will give your drummer's camera a different look and feel than the rest of your cameras. You've got to be sure this fits your style. But if you don't get a good image to track, you're going to be doing it manually. So that's one of the tradeoffs.
A retroreflective (or just a bright white stick) drumstick can produce a lovely smeared object if you are shooting at longer shutter speeds of say, 1/30 or 1/15th second. that's a different topic.

bogiesan




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