PixInsight - Comet Processing

Comet Alignment

updated: 2023-02-09


Alignment of all frames on a comet instead of star or deep space objects (DSOs)

Image Registration is the process of matching two or more images of the same scene by superposition. This requires estimating optimal geometric transformations to align the images with respect to a common reference. Image registration is of crucial importance in all processing and analysis tasks based on the combination of data from sets of images. Some examples are image integrationmultichannel image composition, shared information retrieval, change detection and image mosaicing. These tasks have applications in astronomy, medical imaging, remote sensing, cartography, real-time target recognition and computer vision, just to name a few.


Process > All Processes > Comet Alignment


Debayered light frames with "*_a_c_d_r.xisf  suffix" postfix  from folder "..\registered"


Set of frames in the selected output folder, like e.g. ..\CometStarless

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Add Files

Open the Comet Alignment tool and load the calibrated, debayered and registered frames (Add Files)


Add drizzle files


Set Output Folder

Generate comet path mask

If this option is selected, CometAlignment will generate a new image window representing the comet's path from all positions measured on the input frames. The image can be used directly as a mask to check the computed positions on any of the input frames.


Compute PSF fits

If this option is enabled, CometAlignment will find the comet nucleus centroid by fitting an optimal point spread function (PSF) on each target frame during process execution. This greatly improves registration accuracy, which in turn leads to optimal resolution and signal–to–noise ratio in the resulting integrated image. Combined with multiple fixed images, this option can account for nonlinear nucleus trajectories (curved or with variable speed), or to align images not previously star–aligned, where the comet may follow an apparently irregular and arbitrary path.

If this option is disabled, comet coordinates will be linearly interpolated between the previous and next fixed frame positions during process execution.

Set Parameters

  • click on Show first image
  • Stretch the image
  • click on the comet head
  • do the same with the last image
  • see the result on the right





These parameters set the pixel interpolation algorithm used by CometAlignment to align target frames.

  • Lanczos
  • This is generally the best interpolation algorithm for registering linear images when no large–scale changes are required. Lanczos has excellent detail preservation and subpixel registration performance with minimal generation of aliasing effects. Its main drawback is the generation of undershooting (ringing) artifacts. Still, this problem can be fixed in most cases by enabling a linear clamping mechanism (see the clamping threshold parameter).


Apply the settings to the set of images

and wait..... (this takes a while :) )


A set of comet aligned frames with (hopefully) no stars or other artifacts will be created in the selected output folder.


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