Marey effect

jersmi's picture

How could one achieve this echo effect in QC? How would one iterate the frames and get them to stay on screen and composite cleanly?

https://vimeo.com/35770492

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Scratchpole's picture
Re: Marey effect

jersmi's picture
Re: Marey effect

Sort of, but not. Glad to have memo's msaLumaKey CI to work with. "Luma" suggest the inititial problem Marey had with his beautiful photos capturing motion -- he had to use a black background to prevent overexposure. Capturing discrete frames and how to composite cleanly is what I am thinking about.

jersmi's picture
Re: Marey effect

Follow up: this started as a pursuit for a higher quality effect for multiple exposure (sometimes I have trouble naming things clearly at first). This is an old problem in photography, and has been around for years on the digi/real-time side, with keywords like "frame buffering", "video delay", using the queue, feedback, careful compositing, etc. The problem I can't solve at present is how to get frames composited on screen all at once to look "natural", with controllable number of frames/fps, perhaps interpolation between frames, etc. Photo limits come into play -- for ex., a well lit subject on a dark background works way better.

harrisonpault's picture
Re: Marey effect

This is a complicated problem. I think it would be helpful to separate out different classes of filmstrip or multiple exposure sequence. For example, the use of a dark or monochromatic background yields a more tractable problem, and the use of a totally static background with a locked down camera introduces another dimension to the compositing problem. Move the camera, and you add some 3d manipulation issues. A general solution would be the holy grail of compositing. The outdoor sequence in the referenced Vimeo is a different problem from the dark stage.

If you consider first the original Marey scenario with a dark background, then using a Maximum operator with Composite is a good start. The attached simple composition just uses exponential alpha decay to remove stale frames. I would experiment with the decay function for different trail looks. You may need a queue-based approach if you want to control the number of frames precisely.

To attack static but variegated backgrounds, it may be necessary to use a different strategy, more based on explicit keying, like the Photobooth background composition.

btw, the comments from the author on the referenced Vimeo suggest that it was composited using AE, so if you are familiar with the tools there it may provide other directions for research.

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PTH Trace.qtz17.91 KB

harrisonpault's picture
Re: Marey effect

You made me inquisitive, so here is a basic queue-based Marey Effect. It depends on the relative brightness for compositing, but the "trail length" is the queue size. As you said, above, the camera limits are an important consideration. Using my 1280/1040 iSight with crap dynamic range I easily get blow outs, but the maximum compositing technique doesn't multiply this problem, because it just outputs the brightest pixel for each cell, it doesn't add or multiply them. I suspect this might be more the "look" you are aiming for. It would be cool if my prototype could be refactored using iterators, so you could vary the queue length and the number of frames skipped. I am looking into that, but the logic/order of iterator execution is somewhat opaque to me, and it is not clear to me how to build the composite of composites in an iterator structure.

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pth_queue-based_video_echo.qtz19.67 KB

jersmi's picture
Re: Marey effect

Well done! True, I can't quite imagine how the iterator would handle the maximum composite operator like you have it. Playing around with varying FPS is easy enough, see attached. (I'd prefer controlling fps with the signal patch, but it's unstable for me, so I threw something together here.)

As far as After Effects goes, simply put, that's not real time.

I know there are some fancy algorithms out there for compositing. (HDR, for example). I wonder what Canon uses for their multiple exposure feature in the 5D/1D: http://www.dpreview.com/news/2012/08/06/Reuters-showcases-Canon-multiple...

Here's Canon's bit about "averaging" multiple exposures into one photo:

Quote:
Average

This setting is particularly useful if the same scene will be photographed multiple times, and combined into a finished image with little or no camera movement between shots. Exposure is automatically reduced, proportional to the number of shots taken, to avoid over-exposing common areas or overlapping bright areas. Where overlapping areas do occur, the final brightness level will be the same as the would have been in a single, properly-exposed shot. And, any non-overlapping areas will be darkened.

Unlike Additive, the Average setting takes the same exposure level for each separate original image you shoot (although each can be independently adjusted). Average is ideally suited for a scene like a tripod-mounted camera overlooking a broad area, where you want multiple shots to record the movement of an object like a runner, car or airplane moving through the scene.

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pth_queue-based_video_echo_fps.qtz27.22 KB

jersmi's picture
Re: Marey effect

Progress. Here's a version iterating distance between frames, with interpolation. Compositing is still outside of the iterator, and I can't see a reason to try to recreate it inside an iterator right now. I also pushed the number of frame copies to 32. Set this up to see how many frames/copies I could push, keep the sliders low if your system chokes. The effect is nice, thanks again for being curious, Paul!

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ECHO.qtz47.34 KB

harrisonpault's picture
Re: Marey effect

Very nice effect. Glad my thoughts contributed to something workable.