Mei Lewis Posted May 1, 2012 Share Posted May 1, 2012 I want to make videos where each frame looks like a long exposure photograph. I want to see if I can get the "light trails in the dark "effect that's easy in stills using a long shutter time. I figure if I shoot video at 1/30s shutter time at 30 frames per second the shutter is always open, and I should be able to get a different 1 second long exposure every 30th of a second by combing frames like this: new frame 1 = original frames 1 to 30 new frame 2 = original frames 2 to 31 new frame 3 = original frames 3 to 32 ... new frame x = original frames x to (x+29) ... I planned to combine frames in after effects by overlaying multiple copies offset 1/30s and reducing the opacity of the upper frames. I think the opacity of the bottom layer should be 100%, the next one up 50%, then next 25%, the next 12.5% and so on so that each layer contributes equally to the final image. Problem is the higher frames require very low opacities, the 30th should be 1.86265 x 10^(-7)%, and that doesn't work even with the project set to 32 bits per pixel. Does anyone know how to do what I'm asking? Link to comment Share on other sites More sharing options...
Chris Millar Posted May 1, 2012 Share Posted May 1, 2012 yep, had a play with this but in photoshop (using scripts, I think they call them 'actions'). I did run into similar issues. I think I ended up doing something like taking two images then adding them 50/50- flattening them then taking the result and adding it 50/50 to the next in the series - then repeating that and so on. In your case 30 or is it 29 times That way you only use %50 - but there was some fiddling I think with the layer mode (the math behind the scenes - e.g. overlay vs. multiply vs. normal vs. darken and so on). I thought AE had a filter that pretty much works the same way anyway - motion blur or something ? (I don't think its controls are so direct however) Link to comment Share on other sites More sharing options...
Chris Millar Posted May 1, 2012 Share Posted May 1, 2012 To answer your question a bit more concretely - learning a little computer programming, maybe using something that does a lot of the work for you like matlab - you can do all this in code down to whatever precision you choose. Link to comment Share on other sites More sharing options...
Mei Lewis Posted May 1, 2012 Author Share Posted May 1, 2012 Thanks Chris. Learning enough matlab and other various bits of coding to connect it to something that can work on video files would take a biiiiiit more time than I have right now. I'm only trying to get this effect for fun, nothing serious. AE has motion blur but the filter closest to what I want seems to be one called "wide time". The results aren't great though, I think maybe because of the limited precision being used. I thought of doing similar to your suggestion of mixing down, but in after effects using precomposition.I/'m going to shoot something at 4fps and see can I get that to work before I got up to 30. Link to comment Share on other sites More sharing options...
Chris Millar Posted May 1, 2012 Share Posted May 1, 2012 Good plan. maybe make some testing frames - simple block animations of 255/255/255 vs. 0/0/0 - something you can check the outputs of when you're done. Link to comment Share on other sites More sharing options...
Travis Gray Posted May 1, 2012 Share Posted May 1, 2012 Crazy question, but, any reason to need to do it with video? Could you just do a time-lapse with an SLR? Link to comment Share on other sites More sharing options...
Chris Millar Posted May 2, 2012 Share Posted May 2, 2012 Crazy question, but, any reason to need to do it with video? Could you just do a time-lapse with an SLR? Thing is that he's overlapping the exposures so each frame shares 29/30ths of the preceding (or following) frame. You'd need a set up that could tap in and out of the data stream at will while keeping 30 taps concurrent. It's pretty much having a 10800deg shutter angle. Link to comment Share on other sites More sharing options...
Mei Lewis Posted December 3, 2013 Author Share Posted December 3, 2013 Just got an email about this thread, prompting me to reply. Not sure why I didn't before. My maths for the layer opacities in the first post is wrong, don't know what I was thinking, they should go down as: 1/1, 1/2, 1/3, 1/4, 1/5...1/25 for the 25 layers, and that's easily doable. Here's a test with some more notes in the comments: That has an effective shutter angle of 9000degrees. If anyone's interested I can zip up and upload the entire source for that video, it's a Premiere pro edit. Link to comment Share on other sites More sharing options...
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