PixInsight Tutorial: Comet Stacking & Color Calibration

Comet stacking：

Set up folders 2 folders Debayered, CometAligned. All tools can be found in the process tab

1. Debayer - Add the light. Fit files by clicking "Add files". Under "Output Files" in blue designate an output directory by clicking the little folder icon. Here you will select the debayer folder you created earlier. Click the blue circle on the bottom left(apply global).
   
2. CometAlignment - Add the files from the Debayered folder. From the frame list double click to open the first image and then move your cursor over the nucleus of the comet and Ctrl + left click the head. Open the last frame of the frame list and repeat to align the head. You may need to auto stretch the image if the comet is not particularly bright but I usually prefer not to in order to see the comet head very precisely. Now set the output directory with the CometAligned folder. Finally click the circle button.
   
   
3. ImageIntegration(comet stack) - Let's stack the comet first by adding files from the CometAligned folder and for combination selection choose "median" and then click the circle button at the bottom. Congrats you now have a stacked comet image! Now we can go a step further and get the correct color for our comet.
   
   

Color calibration：

We are going to use the Spectrophotometric Color Calibration tool to calibrate the color of the comet, this will require downloading the Gaia dr3 database. Now SPCC uses the stars to measure the flux of the stars to calibrate the image to the correct color and we have a comet aligned image with smeared stars so this can't work on this image. However we can use the live stacked image from the Seestar to first Calibrate that image and we will copy the same measurements to the comet aligned image and do a manual calibration.

1. Working with the live stacked image we crop in any dithering artifacts
2. If you have BlurXterminator use in "correct only" mode and apply to image.
3. Plate solve the image under script>Astrometry>ImageSolver click OK
4. Pull up Spectrophotometric Color Calibration under process. For white reference we select "G2V Star" (The comet receives illumination from our Sun). red, green, blue filters will be "sony color sensor UVIRcut". Finally make a box selection in an area with no stars that will represent the background and check the box for "region of interest" and select "from preview". Finally click and drag the triangle at the bottom to the star stacked image. In the process console you will see in green the white balance factors, we can use these numbers(write them down!) to do a manual color calibration for our comet stacked image.
5. Under process select the "ColorCalibration" tool. Uncheck the structure detection and select manual white balance and enter in the values we had earlier in the process console. We can again select a background reference and drag and drop the triangle to the stacked comet aligned image. Now you have a correctly calibrated comet! Now you can keep processing with your usual workflow.

before vs after

Final comet

Text and Image credit: Jason Marriott