How do I manually stack multiple photos in Photoshop so each image contributes equally?
Asked 5/30/2014
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2 answers
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I want to combine several photos into one brighter image in Photoshop, but do it manually rather than using an automated stacking feature. My idea is to place each image on its own layer and adjust layer opacity so every photo has equal weight in the final result.
The problem is that if I set every layer to the same opacity, the stack becomes semi-transparent overall unless one layer stays at 100%, which seems to give that image more influence than the others.
What opacity should each layer use so all images contribute evenly? Also, should there be any blank background layer in the document?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
5
When you set the opacity of a layer 50%, what you get is 50% of that layer, and 50% of all the layers underneath it combined.
For this reason you should set the bottom layer to 100%, then layer above that to 50%. Now you have a perfect balance of the two layers. The layer above that should be set to 33%, meaning your image is one-third that layer and two thirds of an even blend of the bottom two layers. The next layer above that should be set to 25% and so on.
Unfortunately you can only specify opacity in whole numbers so you start to introduce a bias that gets worse the more layers you add. One solution to this is to stack as many layers as you can, and then merge those layers and make the result 100%, then start again by placing the next layer on top of that at 50%.
Needless to say you should set your image to 16-bit mode when stacking to avoid rounding errors.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
12y ago
0
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Yes—if you want an equal blend, don’t give every layer the same opacity. In Photoshop, a layer set to 50% opacity contributes 50% of itself plus 50% of everything below it combined.
To make all images contribute equally, stack only the photo layers (no blank background layer), then set opacities like this from bottom to top:
- bottom layer: 100%
- next: 50%
- next: 33%
- next: 25%
- next: 20%
- etc.
In general, the nth layer from the bottom should be set to 1/n opacity. That way, each new layer is blended evenly with the combined result below it.
A blank white or transparent background layer should not be part of the blend, or it will affect the result.
One limitation is that Photoshop opacity is typically set in whole percentages, so with many layers you may get small rounding errors. A practical workaround is to blend a group of layers, merge them, then continue stacking the next images on top using the same approach.
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