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Can anyone explain the difference between - Sigma Clipping, Median & Average Combination?

- Superstar1
**Posts:**6**Joined:**Tue Jul 17, 2012 5:44 pm

Superstar1 wrote:Can anyone explain the difference between - Sigma Clipping, Median & Average Combination?

Have you looked at the technical details page on the DSS website?

http://deepskystacker.free.fr/english/technical.htm

There it suggests

Which stacking methods

If you are looking to create images with star trails, average is the best method.

In all others cases you should use Median stacking with small stacks and kappa-sigma with large stacks.

The details of each method is also given

Stacking Methods

Average

This is the simplest method. The mean of all the pixels in the stack is computed for each pixel.

Median

This is the default method used when creating the masters dark, flat and offset/bias. The median value of the pixels in the stack is computed for each pixel.

Maximum

This is and ultra simple method which should be use with a lot of care. The maximum value of all the pixels in the stack is computed for each pixel.

It may be useful to find what is wrong in a stack by exhibiting all the defects of all the calibrated images.

Kappa-Sigma Clipping

This method is used to reject deviant pixels iteratively.

Two parameters are used: the number of iterations and the standard deviation multiplier used (Kappa).

For each iteration, the mean and standard deviation (Sigma) of the pixels in the stack are computed.

Each pixel which value is farthest from the mean than more than Kappa * Sigma is rejected.

The mean of the remaining pixels in the stack is computed for each pixel.

Median Kappa-Sigma Clipping

This method is similar to the Kappa-Sigma Clipping method but instead of rejected the pixel values, they are replaced by the median value.

Scopes: Meade 8" SCT, Skywatcher 127mm Mak

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For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)

For companionship: Mid Cheshire Astronomical Group.

- Gfamily2
**Posts:**324**Joined:**Thu Jun 25, 2015 10:38 pm

Many thanks, well explained

- Superstar1
**Posts:**6**Joined:**Tue Jul 17, 2012 5:44 pm

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