Actual Step

Processing Mosaic Images

updated: 2023-11-24


Avoid time differences between ASIAIR and mount leading to errors durings GoTo operations

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The following steps are based on my first attempt to capture mosaic images of NGC7000 (North America Nebula), see the preparation steps here.

Post-Processing using PixInsight (Option 1: Rough Mosaic with StarAlignment)

  • To calibrate, debayer, reject bad frames, register, normalize, and integrate all 4 sets of images: run the PixInsights Weighted Batch Processing script on each set individually. This will consume some time depending on your computer HW and the total number of frames. Here is the final copy from the WPP execution monitor (on frame set 1) as an example:

  • Next apply Photometric Color Calibration (PCC) and SCNR (to degreen the images) to all master light frames

  • After finishing the pre-processing of all 4 sets open the Star Alignment process and open all 4 master light frame from the previous step. 
  • Select one of the frames as master frame
  • Select Thin Splines under Registration model
  • in Working mode select Register/Union - Mosaic and enable Frame adaption
  • Enable Frame Adaption: helps to create seamless mosaics to smooth the illumination and background between the selected images.
  • Expand the Star detection tab and increase Noise sales to 1
  • Expand the Star matching and increase RANSAC Tolerance to 6.00, iterations to 2000 and enable Restrict to Preview Options
  • For difficult star alignment situations: Help Star Alignment know where the images merge by creating preview boxes in the first 2 images to be merged by creating preview boxes in both images that cover approximately the overlapping area in the image: 
  • Tip: when trying to integrate a single master light frame into an already combined mosaic, select the mosaic frame as reference frame and click to select the single frame (bring it in front of the mosaic) before starting the integration, otherwise the single frame might be ignored or the new mosaic might be limited to the single frame instead of being integrated into the main mosaic image. 
  • If a meridian flip was performed during the capture phase of one of the panes, you must rotate the flipped master light frame 180° before attempting to merge it with the non-flipped images.
  • With image *0001 selected as the reference image, apply the StarAlign process to image *0002.
  • Repeat the last 2 steps for the remaining images.
  • This is the resulting image:

  • Next, you should rotate and crop the image for best fit using PixInsight's Dynamic Crop feature. 
    Hint: Depending on the final perspective ratio of the image, you can set a ratio of, for example, 3:2 between the horizontal and vertical dimensions,
  • This is the resulting image (more or less fully processed):

There are other ways to integrate mosaic images, see the links at the top of this page. 

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