Multiple exposure, or “double exposure” shots may not be possible with most digital cameras, however, they are easy to do after the fact using the GIMP photo editing tool! It is really simple, and I’ve used it to do some cool light painting combinations that I’ll display after the “read more” button.
The process for doing this is pretty easy, you’ll just need a camera and a (free) copy of GIMP. If you have a Canon DSLR, I would highly recommend a remote trigger, as the one linked is dirt cheap, and will allow you to take shots without actually touching the camera. Important for light painting, but especially if you’re going to combine photos like the one (from this radial-engine model light painting article) above. In this case the camera was held still while the vise was rotated, making a painting of the rotary engine cycle at three points.
If the photos are aligned the way you want them, simply open one photo using GIMP, then add the other pics you’d like to combine into other layers. In the Layers dockable dialog box select “lighten only” and it will act like you took both shots on the same piece of film (if you were using film). It should be noted that if you do this, the light from each picture will be added together, eventually becoming a lighter and lighter shot. Because of this, light paintings tend to work well for these double exposure pictures since there isn’t much background light.
If everything isn’t lined up as you’d like, GIMP, of course, lets you move the layers around. The two bottom photos in the gallery use this as well as some more advanced techniques to put a light-painted Pacman (first seen in this post) running through the woods and eating the moon.
The foreground was selected using the select => by color to select the trees, then select => invert to select the background that wasn’t needed. The “delete” key then took care of this. The background was the trees and night sky and the display mode was left as normal. The middle layer, Pacman, was then moved about and displayed as “dodge”. Using this technique, you should be able to intersperse whatever you want in between items in a photograph. Kind of an advanced “double exposure” technique.
Be sure to check out my other Gimp-related articles for some tutorials and other stuff that I’ve done with this excellent program. I’m definitely still learning how to do this, so if you have any better techniques etc, be sure to let me know in the comments!