Can I average or median-blend adjacent timelapse frames to reduce low-light noise?
Asked 1/9/2014
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I’m shooting a timelapse on an iPhone 5s. In daylight it looks fine, but after sunset the low-light noise becomes very noticeable. I’m wondering if I can combine groups of adjacent frames—say 10–12 photos at a time—using an average or median blend to reduce noise while keeping the same resolution, even though I’d end up with fewer frames overall.
As a bonus, I’d also like this to make motion from people or cars look less abrupt. I can export either a 4K video or the original image sequence. Is there Mac software, ideally simple and inexpensive, that can do this kind of frame averaging/stacking for timelapse work?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
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I'm not aware of any one-click utility for this, nor anything that can run off a video stream directly, but if you were to export the individual frames to images first, there's a bunch of ways to get averages (either median or mean) from a stack of images.
You'd most likely be looking at selecting each stack one-by-one and averaging into single frames, then merging them back to the video stream afterwards.
- Photomatix (best known for its HDR capabilities) can also do averaging of multiple shots
- You can merge a Smart Object in photoshop into an average value (mean or median)
- Gimp, Pixelmator & Acorn all support layers, so there's a possibility they can merge those into a mean/median (I'm not overly familiar with them though)
If you wanted to maintain the frame-rate, you could, for each frame, average it with the 5 shots before and 5 after; a kind of rolling-average if you will. You'd probably need to script that to maintain any kind of sanity though—though I note you're not after anything too complex.
^^Rolling average with three frames.
For anyone looking for a more advanced method, this could probably be done in Matlab if you happen to have access to it (its got good, simple image importing and can do fairly arbitrary maths on images as 2D arrays). Alternatively image-magick can be used for some scripted averaging.
Originally by user889. Source · Licensed CC BY-SA 4.0
user889
12y ago
0
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Yes—stacking adjacent frames with a mean or median blend can reduce random noise, and it can also smooth moving subjects in a timelapse. The tradeoff is that combining 10–12 frames into 1 lowers your effective frame count unless you overlap the groups.
Based on the answers, there isn’t a well-known cheap “one-click” Mac app specifically for doing this directly on a timelapse video stream. The practical approach is to export the timelapse as individual images, blend each group into a single frame, then reassemble the sequence into video.
Tools mentioned that can do this kind of stacking include:
- Photoshop: Smart Objects can be stacked using mean or median
- Photomatix: supports averaging multiple shots
- Layer-based editors such as GIMP, Pixelmator, and Acorn may also be able to do it
Median blending is especially useful if you want moving objects to be suppressed or softened; averaging tends to produce motion blur/ghosting instead. For best results, work from the original image sequence rather than a compressed video export.
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