PixInsight - Frame Selection

Automatic Selection using Sub-Frames Selector

updated: 2021-08-20


Evaluating and Rejecting Bad Frames (e.g. with clouds, meteoroids, airplanes, vibrations, blurred pictures …).
Facilitates subframe evaluation, selection and weighting based on several subframe quality related measurements.

Remark: Do not confuse the Process Subframe Selector with the Batch SubFrame Selector   !!)


Menu Process 🡺 All Processes 🡺 Subframe Selector


aligned original images (light, dark, ...)


approved pictures, should be stored in subfolder "1_Approved"

bad ones will be moved to a subfolder named "1_Rejected"

Previous Step

Picture Shooting

Next Step

Debayer Function







Target Subframes: Add light frames
  • Open all images (subs) that you want to include. 

Remark: importing a 56MB RAF file from a Fuji takes more than 1 minute!


Set System Parameters

The settings depend on your camera and equipment. 

  • Subframe scale:
    Subframe scale is measured in arc-seconds per pixel. This affects star-related measurements and is only required if Scale Unit is set to arcseconds. In this case use the Optical Scale Table for the correct value, the ZWO ASI294 has a value of 1.592 arcsec/pixel on f=600mm .
  • Camera gain
    in electrons per Data Numbers. This affects star-related measurements. 
    This is only required if the Data Units are are set to electrons (e-).
  • Data unit - select one of:
    • electrons (e-): then Camera gain must be set
    • Data number (DN)


Measuring (Apply Global)

In the Routine setting (top of the window) select Measure Subframes - then click on the blue circle at the bottom to start the measurement.

... this can take a while, depending on the size and character of your subs..


Check Measurement Table

Meaning of FWHM quality values:

1 to 3:                quite good

2 to 5:                medium quality

over 5:                unusable

Click on high spikes on the plot to deselect bad subs.


Bookmark the best sub as reference sub

the reference sub in this example is #8: 20170921_M8_FUJXT1_7450_a.xisf 


Output good subframes

Once subframes have been approved or rejected, and optionally subframe weights applied, the approved subframes may be copied and/or overwritten to output directories by selecting "Output Subframes" option of the the Routine dropdown and Executing the process Globally. 

Output directories for approved subframes may be specified in the  field, use e.g. "approved" as output directorOutput directoryy name. 

If a directory field is left blank, the associated subframes will be written to the same directories as their corresponding target files. The prefix and postfix fields specify prefixes and postfixes that will be prepended and appended to the file name of each copied or overwritten subframe. To record subframe weights in the FITS headers of the copies specify a FITS keyword in the Weight keyword field.


Next Step: Working with Master Calibration Files

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