Night Photography Resource

Sometimes conditions and the limits imposed by cameras will force you to choose to use a high ISO speed. There is nothing wrong with a high ISO speed, but some people do not like the additional grain that this adds to their picture. Image stacking, a technique from astronomy, can help improve your high ISO pictures by reducing noise.

Overview

Noise in pictures appears as random specks of light superimposed over your picture. Since the contents of the picture are non-random (assuming you have no movement in your picture), you can take multiple pictures and then blend them together so the random noise is canceled out.

Why Use This Method?

There are several noise reduction programs and tools available which perform similar work on a single photograph. The main drawback to using the other tools is that they tend to cause blurring when they remove noise. This technique is preferable since it maintains the sharpness of the original photograph.

How to

1. Using a tripod, take a series of pictures of the same scene using the same settings
2. Import the pictures into your favorite image editing program, each as a separate layer
3. Set the opacity of the bottom layer to 100%, the next lowest layer to 50%, the next lowest layer to 25% and so forth; halving the opacity for each subsequent layer
4. Flatten the image into a single layer and save normally

Examples

On the left is a picture taken at a high ISO speed without any compensation, and on the right is a composite made from stacking six high ISO speed pictures together. Notice that the picture on the right has reduced grain but still maintains its sharpness.