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M1 Crab Nebula and PixInsight Workflow

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M1 captured 13th March 2016 with 127mm F7.5 APO triplet 0.8x reducer; Skywatcher AZ-EQ6-GT, Atik 314L+ OSC, Sequence Generator Pro, PixInsight. Not sure I've got the focus nailed although it was set using the auto focus routine in SGP.  14 600sec light frames with superbias from 200frames and 50 flats. No darks used (conscious decision following comments on this forum about the need for them). 

PixInsight Process; Preprocess -> Super Bias from bias frames - Master flat from flats with bias subtracted - Light Frames calibrated, debayered, cosmetic corrected, weighted, registered and integrated. Processing - Dynamic Crop - Dynamic Background Extraction - Colour Calibration - SNCR - MLT Noise Reduction (masked) - Stretched with Masked Stretch - Local Histogram Equalisation (masked) - Curves transformation - MLT Noise Reduction (masked) - ACDNR - Reduce Colour background/contrast with MLT (masked) and Histogram Transformation(masked)  - Curves Transformation - Boost Colour in nebula with MLT (masked) and Colour Saturation - Curves Saturation overall - and Curves Saturation to stars only (masked) .

Any pointers on steps to improve it or ways to improve my processing welcomed - still wading through tutorials and videos to get my head round PixInsight 


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Very fine image. I've never tried my hands on M1, but what I understand from this forum is that it can be a difficult target to get right.

To me it seems that you have overdone some of the brighter stars. The core of the large star  on the right has a blueish core and a halo/corona that is much more red.

Also you seem to have some chromatic abberation.

I've seen a short tutorial on the Pixinsight forum how you can correct for CA:

separate the RGB channels, put them through StarAlignment with one of the channels as a reference. Then stack the three resulting images.

Simple and straight forward, but with amazing results (at least in the presentation on PI forum)


Here's a link




Edited by wimvb
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Wim makes a good suggestion with the stars above to get the channels to line up better. Also, i wouldnt use Masked Stretch for taking the image non-linear, it gives a very soft looking result. I found that using Histogram Transformation gives a much better contrast base to work off. If you wanted to work on the stars after that then i would then create a masked stretch version and blend its stars with the HT version using a star mask and Pixel Math. Theres a good tutorial for this method from John on this page:  cloudedout.squarespace.com/blog/?offset=1418583715170


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Good shot of a difficult target. Not sure if its the focus but the stars look a little blurred. Worth trying the masked stretch on just the stars as Callum suggests. I would recommend Harry pages tutorials for PI he does a good one on the masked stretch for blending in the stars

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