PixInsight - Master Calibration Files

Master Dark and Master Bias Calibration Frames

updated: updated: 2021-08-20

Purpose

The  Image Integration module is used to generate the master bias and dark frames 
The same settings will be used in this module for generation of master bias and dark frames. So we'll run the integration twice: first for the bias frames and then again for the dark frames (bias subtraction of dark frames will take place with the IC tool).

There are several important settings to pay attention to:

  • Don't normalize the images, because the bias pedestal must be preserved. Both normalization methods in the Image Integration and Pixel Rejection (1) sections must be disabled (No normalization setting).
  • To be meticulous, the image weighting feature must also be disabled. We want to perform a strict average of a large number of frames, rejecting only clear outliers.
  • To reject possible outliers, I recommend the Winsorized Sigma Clipping algorithm, in case we have a large number of bias and dark frames. A permissive clipping point of 3×sigma can be useful.. 

Activation

Process 🡺 All Processes 🡺 Image Integration

Input

Dark and Bias calibration frames

Output

Master Dark and Bias frames

Previous Step

Image Integration

Next Step

Image Calibration

Tutorial

PixInsight — Master Calibration Frames: Acquisition and Processing

Step

Description

Master Dark Frames

Master Bias Frames

1

Open the Image Integration module

2

Add Dark or Bias frames

3

Image integration settings to be used

Important: 

  • don't normalize the images
  • image weighting must be disabled (all weights = 1)
  • Scale estimation: 
    • Biweight midvariance
    • or MAD (Median absolute deviation)

4

Pixel Rejection (1) settings

  • don't normalize the images
  • for 5 to 30 frames: use Winsorized Sigma Clipping 
  • if more: use Sigma Clipping

4a

Pixel Rejection (2)

5

Run the Integration

Click on the (Apply Global) or hit F6

The master dark frame on the right is a typical result of an ASI294, you can clearly see effect from the heat generated by the electronic components behind the  sensor chip (image is stretched).

6

Save the master calibration files

use meaningful file names, see example


ASI294_Master_Dark_180sec-10C-20x.xisf


ASI294_Master_Bias_180sec-10C-20x.xisf

7

Next Step: Master Flat Generation (I)




Read this article for more information: PixInsight — Master Calibration Frames: Acquisition and Processing

and: Astrophotography by Rob Kantelberg (astro-imaging.com)

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