How can I automatically create a composite of a moving subject from many aligned frames?
Asked 7/7/2014
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I have a sequence of already aligned photos with a stationary camera and background, and a subject moving through the frame. I want to combine them into one image so the subject appears in each position, without transparent blending or manually masking dozens of layers in Photoshop. Is there an automated or semi-automated workflow for this?
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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There is a simple method to automate the process using Photoshop. It could be recorded as an action or scripted.
Load all of the images into a stack and take the median of each pixel (there is a built in function to do this, might just be in Photoshop extended though). This should give you an image of just the background.
Load up the first image and paste the background image over the top as a new layer. Set the blending mode to difference. Copy the result, paste it to a new layer, desaturate (under the image menu) it then apply a threshold (image menu again) of about 5-10. This should give you a black and white mask of just the object in motion. Create a new layer mask and past the black and white image in. Delete the other layers. You now have a cut-out of the object.
Create a new document and paste in the background. Paste in the cut-out. Repeat the above steps to cut out each image and paste them in turn.
Flatten the result, and you have your montage. It would take some work but if the number of image was constant you could create a Photoshop action to do all this.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
12y ago
0
Generated from our catalog & community — verify before relying on it.
Yes. With a locked-off camera and static background, you can automate much of it.
A practical Photoshop-based workflow is:
- Load all images into a stack.
- Create a clean background by taking the median of the stack (this removes the moving subject).
- For each frame, place the background over that frame and use Difference blending to isolate what changed.
- Desaturate and apply a Threshold to turn that difference into a black-and-white mask.
- Use that mask to cut out the subject from each frame, then place the cut-outs together in a new document.
This can be recorded as an action or scripted for many frames.
If the images are not perfectly aligned, use software with image registration/alignment first. Panorama-stitching tools can help align frames and even output layered Photoshop files.
An alternative is to capture the effect in-camera: expose for the background and use repeated strobe flashes during a long exposure so the subject appears multiple times in one frame. That avoids post-processing, but requires suitable lighting and setup.
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