Noise Reduction and Image Stacking Example
Antennae Galaxies: NGC 4038 - 4039 (Ring Tail Galaxies) - SCROLL DOWN TO SEE ALL THE IMAGES!

Images Copyright 2006, Dick Locke.  All Rights Reserved.  Contact and Image Use Information

This shows how the process of digitally combining astronomy images can reduce noise and bring out areas that otherwise are too dim to see.  Below: a relatively noisy single image, 4 minutes exposure at ISO 800.

Note the Noise: Antennae Galaxies: NGC 4038 - 4039

The image above is a single, 4 minute exposure, with subsequent curves modification in Photoshop.  If your monitor is adjusted appropriately, you should easily be able to see a good bit of noise, especially in the darker areas.  You may not notice the "Antennae" though.  This very faint feature just about lost in the noise.  Below: noise reduction on single image...

The crop above is from the 1st image, but reflects one application of a  noise reduction tool ("Neat Image") at default settings.  I think its done a pretty good job.  Neat Image allows to you specifically sample the noise a featureless area of your image.  This works well for astronomy images that have some space between stars, such as this one.

Note the Antennae View

Stacking has brought out a very dim area of the image, processed in my normal workflow.

The bottom image is a digital combination ("stack") of  10 x 4 minute = 40 total minute exposures .  More exposure would will be better (as would better focus and tracking- the usual stuff!)!   The above view shows the dim, antenna trails, along with some of the noise and processing artifacts due to extreme image stretching.  

There is a mathematical formula* that applies: Generally, the image noise is reduced by the square root of the number of exposures. 

*I hope someone will correct me if the formula wrong ;-)

Takahashi TOA 130 (a 5" APO refractor) and Canon EOS D20a.   My current image processing workflow is here.

The "normal" antennae galaxy page is here.

Dick Locke's HAS Astrophotography Index

The other HAS Pix from 3/25/2006 are here.

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Copyright 2006, Dick Locke.  All Rights Reserved.
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