Today’s Question: In Photoshop is there a straightforward automated way to combine multiple layered images so that each layer has equal value/opacity when combined, to create the equivalent of a multiple exposure? I use a formula to reduce the opacity at each layer (50%, 33%, 25%, etc.) but it is time consuming and repetitive.
Tim’s Quick Answer: A better approach here, both in terms of convenience and a more accurate multiple exposure effect, would be to convert the blend mode for each layer to the Screen blend mode, and then apply overall adjustments as needed to fine-tune tonality.
More Detail: When you combined two layers using the Screen blend mode, you are creating the same effect as a double-exposure effect. In other words, the two exposures are combined to create a brighter image with blended details.
It is very easy to change the blend mode for a series of image layers. The first step is to create a composite image that includes layers for the individual photos you want to combine into a multiple-exposure effect. From Adobe Bridge you can select the photos to combine and then choose Tools > Photoshop > Load Files into Photoshop Layers from the menu. In Lightroom you can select the images and choose Photo > Edit In > Open as Layers in Photoshop.
You don’t need to change the blend mode for the Background image layer to the Screen blend mode, but I prefer to do so anyway because sometimes I like to change the order of the layers. If you want to be able to change the blend mode and layer order for the Background image layer, you’ll need to convert it to a “normal” layer by double-clicking on the thumbnail for the Background image layer on the Layers panel and clicking OK in the New Layer dialog that appears.
You can then select all of the image layers by clicking on the thumbnail for the top-most layer on the Layers panel, then holding the Shift key on the keyboard and clicking on the bottom-most layer on the Layers panel. If you have not converted the Background image layer to a normal layer you can exclude that layer from the selection.
Finally, you can change the blend mode for all of the selected layers. Click on the blend mode popup (it isn’t labeled as such, but the default setting is “Normal”) and choose “Screen” from the popup list. This will create the multiple exposure effect for the selected layers.
To produce a “normal” multiple exposure effect with this approach you would need to capture images that are darker than the correct exposure. The specific exposure compensation required will depend on how many images you plan to combine. If you did not apply such a compensation, the resulting image using the Screen blend mode will be rather bright. You can simply add a Curves adjustment layer at the top of the Layers stack, however, to apply a darkening effect to the overall result. And, of course, if you’d like you can also vary the contribution of each image layer to the overall effect by reducing the Opacity setting for certain layers.
In general, however, you should find that by simply converting all of the image layers to the Screen blend mode and applying an adjustment to darken the overall result, you have a great starting point for a multiple exposure composition.