Making long exposure video from normal video
Posted 01 May 2012 - 03:29 AM
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?
Posted 01 May 2012 - 03:54 AM
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)
Posted 01 May 2012 - 03:58 AM
Posted 01 May 2012 - 08:43 AM
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.
Posted 01 May 2012 - 03:46 PM
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.
Posted 01 May 2012 - 04:06 PM
Posted 01 May 2012 - 10:52 PM
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.
Posted 03 December 2013 - 01:28 PM
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.