Process Multiple Exposures by Averaging Images

• By: Luis Argerich

There are many techniques and things you can do taking multiple exposures of the same scene: HDR, noise reduction, increasing resolution, simulating long exposures and many others. In this short article I will discuss Averaging Images as a way to improve a scene or to create an abstraction from a scene.
 

 
Tools :

To average images you can use photoshop, Gimp or any photo-edition software. The recipe is simple: load each image as a layer and set the transparency for the nth layer as 1/N.

For example if you have 5 layers transparency would be:

 
Another approach is to use Image Magick, a free software that can be used to do many interesting things on your photos. I use it a lot for batch cropping, resizing and to create composites using different techniques. Once you have downloaded and installed ImageMagick you can average a number of images using the following commandline instruction:

convert *.jpg -average result.jpg

Averaging can be used in static scenes to create a new photo with less noise. Noise is reduced in the function of the square root of the number of images. So if you average 25 shots you have 5 times less noise than in a single image.

Averaging can also be used in non-static scenes to simulate a long exposure.

For example you can simulate a 4 hours exposure of a sunset to see how many different colors you can get as in this example:

A four hours exposure would be impossible as the photo would be blown but a 4 hours average is possible. Averaging skies is a good way to get a surprising abstract combining all the shapes and colors in a time span.

You can try this with the sky or any other scene, take many shots one after the other and use average to find a surprising result. You can average a complete day or a complete night, the results will be surprising.

• Category: Tips
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