NGC1491 - Fossil Footprint Nebula
Emission Nebula  - about 11K LY away - in the Constellation Perseus

Both the recent weather and near term forecast are less than stellar - so photon collection is not possible. I have decided to rework, from the subs, an image I did two years ago, but was a bit disappointed with the result of - despite 30 hours of NB data. 

As well as getting a hopefully improved image I also wanted to do a small processing experiment relating to image integration. When learning PI I used SFS and added a FITS Keyword to each image for later use during Integration. When NSG came along I switched over and became quite comfortable using it. Then PI enhanced their weighting and local normalization so that method has been used recently as well. In reprocessing this image I have integrated the Ha data - individually -  using all three methods. My results are no doubt equipment and location dependant. This image was taken with decent amateur equipment and shot in a Bortle 3-4 zone (based on scale descriptions I have read). Also I have no strong gradient inducing local light sources and usually shoot through the meridian. The moon could be considered gradient inducing since I do not hesitate to shoot NB under a full moon. To compare results I took each Ha integration and performed DBE / NoiseXTerminator / BlurXTerminator / StarXTerminator on each unstretched integrated image. This allowed me to review the nebula only results using STF.

I aint no expert but this is what I found. NSG normalization will find and enhance any gradient that is present - perhaps due to less than perfect flat fielding or sensor inconsistencies. I have seen in the past where the image background - for both NB and BB, using different brands of filters, had this issue to some degree. I had already stopped using NSG but wanted to include it here. Both PI LN and SFS weighting produced more acceptable results. PI LN will subtly enhance any gradients in the image, while SFS seems to just look a bit smoother and less contrasty. Ultimately, for this image I chose the PI LN integration because it gave a bit more contrast in the fainter nebula regions and was easy to process out of the background when stretching the image.

So - for me - since I have very little gradient to deal with (yes, lucky me) using any local normalization is probably not necessary and is more than likely problematic. For BB I will probably continue to use SFS and FITS keyword weighting, for NB I will continue using PI’s LN process.

I also did a quick test to see if I could use PI’s SPCC on an unstretched NB image composed of a stars only combined Ha / OIII / SII image. This failed miserably - but if you could get it to work you might get BB like stars to add back in to a starless NB image.

CS,
Lenard