SharpCap Forums

First of all, gradient removal and hot pixel rejection have MASSIVELY increased my enjoyment of using SharpCap for live stacking. The two together have been game changing. Can't thank you enough for implementing these, Dr. Glover. Now, on to the thing.

If there's one thing I dislike almost as much as taking darks, it's taking flats. Hence, I would like to request that the polynomial order of the gradient removal be increased from linear to at least quadratic, if not fourth order, which I believe is as high as most astro post-processing software goes. SiriL, APP, StarTools, PixInsight; I believe all will do up to 4th order background extraction. Obviously this will not address dust shadows, it may not always be appropriate, it may not be perfect, you may have to increase the density of sample points for higher order fits, you may have to reject sample points that fall on nebulosity, etc. Still, I feel like it would be a massively useful feature.

M51 live stacked in SharpCap with HPR and gradient removal but no flats:



The exact same image with only 4th order background extraction in SiriL (note that this automatically neutralizes the background as well):



Thanks for your time and consideration.

I was happy to buy a Pro Lifetime Membership to Sharpcap. It is not only excellent, but wonderfully supported. And, anything that makes Darks or Flats easier would be greatly appreciated. Not just +1, but +3 because each New Feature has been hugely beneficial for my hobby's enjoyment!

+1

Hi,

thanks for the suggestion - if people want to share a few frames that would benefit from higher order background subtraction then that would help me be in a position to investigate this.

One thing will be to see how numerically stable the calculations are with a higher order polynomial. Least absolute deviation (which we use to avoid being affected by outliers) needs an iterative solution, which is not always stable. For linear removal there are only 3 unknowns to be calculated. Quadradic has 6 and quartic has 15 if I have counted correctly.

cheers,

Robin

Thank you very much for looking at this, Dr. Glover. Here are a selection of lights.

< links removed because they were in error >

https://drive.google.com/file/d/1WnrZrd ... sp=sharing

I've included lights from a couple of M101s, different nights and sky conditions, an M27, and an M51. All shot with a reduced C8 with the ASI533MC. I have some lights from my 70mm refractor, but honestly the sensor is so well illuminated there that there is practically no vignetting.

Edit: My apologies but I realized that 3 of those files were inadvertently from the end of the sessions and not the beginning, meaning they were not usable lights (dawn's early light or tracking limit reached). I will replace them shortly.

+1 for requested feature (if doable)

Paul

What an excellent idea. I never take flats and would be so useful this feature

+1 providing it doesn't slow the process much

I would like to +1 this feature.

The current Hot Pixel Removal and background subtraction features of SharpCap are excellent. This feature (if possible) would be a great addition.

Dr. Glover,

As I mentioned in my edit above, 3/4 of the files I linked above were incorrect. Here is a link to the correct files; all of them should be usable lights. My apologies for the inconvenience.

I've also added an M13, which I expect to be a tough case, and a Crescent Nebula, also perhaps tough (I tried SiriL on it and while it was greatly improved it definitely was not perfect).

https://drive.google.com/drive/folders/ ... sp=sharing