Can I create a video that shows a long exposure building up over time?
Asked 4/10/2012
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2 answers
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I want to make a video where the image starts dark and gradually brightens as if a long exposure is accumulating light, including moving lights leaving trails.
I’ve considered two approaches:
- Shoot many short exposures in sequence and build a video where each frame is the cumulative sum of the images.
- Extract intermediate exposure data from a single RAW file so I could reconstruct the exposure at different moments in time.
Is approach #2 possible with RAW files? If not, what’s the best practical way to create this effect, and are there any limitations with the short-exposure stacking method?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
4
First off, #2 is not possible. #1 is kind of possible although most cameras have relatively limited buffers so I would advise using video to produce a video, rather than RAW images. You wont need the extra resolution anyways.
While I have not tried this, here is my intuition which would require some scripting at least:
- Shoot a video of your scene at the fastest frame-rate your camera supports.
- Split the video into frames (free tools can do this)
- Sum each frame and the next few (4-9 let's say) consecutive frames into a new frame.
- Create video from the new frames yo created.
This will create an interesting rolling exposure effect video since frame 1 will be the sum of frames 1-10 (say), then frame 2 would be the sum of 2-11, frame 3 that of 3-12, etc. Your video here can be of arbitrary length. If you do this, please post it somewhere and let us know!
If all you want it to show a single exposure progressing, then you can cheat by getting an OM-D E-M5 which will output this directly over HDMI. All you have to do is Enable the Live-Bulb mode and start a bulb exposure. Any HDMI recording device can be used to capture the stream.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
14y ago
0
Generated from our catalog & community — verify before relying on it.
RAW files do not contain a time history of the exposure, so you can’t recover intermediate stages from a single long exposure.
To create the effect, use a sequence of frames and build the exposure progressively in post. Two workable options:
- Shoot stills continuously and cumulatively add each frame to the previous result.
- Or, more simply, shoot video at the highest frame rate available, extract the frames, and combine each frame with several following frames to create a rolling long-exposure look.
A few caveats:
- If you use sequential stills, there may be tiny gaps while the shutter closes/reopens or the camera writes files. Longer individual exposures relative to the gap help hide this.
- Each source frame must avoid clipping/overexposure, or the cumulative result won’t be accurate.
- Stacking many underexposed images is not identical to one clean long exposure: dynamic range is reduced and noise can build up.
So: #2 is not possible; #1 is the practical route, and using video frames may be the easiest way to get a smooth result.
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