Digital Multiple Exposure

Most traditional film SLR cameras have an option which allows the photographer to create "Multiple Exposure" images where the same frame of film is literally exposed several separate times. This can be used to create various special effects; the most common of these being the appearance of ghostly semi-transparent objects in the frame.

With the exception of a few models, digital SLR cameras tend to lack this capability and as a result we've seen less of this style of image in recent times. It turns out that it is very simple to duplicate this technique using three individual shots and Photoshop Layers. There's only one thing you need: Screen Blending Mode.

Well, that and a few images. In order to create a traditional multiple exposure, you'll want to underexpose the frames that will be combined. Remember: exposure is an additive process - if you combine two images, the resulting overlap will have all the luminosity of the first image plus that of the second image. Knowing this, we can quickly determine how much underexposure that we'll need in order to end up with a final composite of the correct exposure.

3 Underexposed images

Keeping in mind that each stop of exposure equals a doubling of light, it's easy to calculate our target underexposure for each frame making up the final composite. Two frames? Underexpose each by 1 stop. Four frames? 2 stops each. For Three frames, you'll want to stop down by 1.5 stops on each - on some cameras you may have an easier time doing 1+2/3 stop, if your dials are set up in increments of a third. The simplest way to set your exposure is to just set your camera's Exposure Compensation to the amount - just remember to reset it when you're done.

Once you've got your images, load them all into Adobe Photoshop. Arbitrarily pick one of your images to be the "master" - it doesn't matter which one you choose. Then, copy each of the other images and paste them into the master; when you do this they'll each become new Layers in your document. Now it's time for the magic!

Screen Blending Mode

On all of the pasted image layers, switch the Blending Mode to Screen as seen in the image above. The Screen Blending Mode will simulate the additive exposure behavior of film and you'll be left with a composite that is the sum of each of your individual frames...

Flowers with Ghosted Daisies

The image above is the result of combining the three exposures shown in the beginning of the article. Notice how the colorful flowers remain sharp, while the white daisies appear partially transparent. This is because the colored flowers remained in the same place during all three shots, while the daisies were moved around. A slight crop and a few tweaks round out this image; total time in Photoshop was less than 10 minutes.

Keep this simple technique in mind the next time you're looking for some inspiration. With a little planning and a simple Photoshop trick, you can revive the fading art of traditional multiple exposures.