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Dealing with Gradients: GradientXTerminator vs PixInsight


Euan
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Having an OSC camera with a IDAS light pollution filter I spend the majority of my processing time battling against colour gradients. I've bought GradientXTerminator but I am also running a trial of PixInsight so here a completely un-scientific test to see which one works better for me.

This is a 1 hour 40 min stack of M45. Deep Sky Stacker (DSS) seems to mess up flats for me, so I calibrated the subs with 50 x Bias and 50 x Flats in Maxim then stacked them in DSS. The basic levels and curves were done in PixInsight, then then same file put into Photoshop.

I played with the GradientXTerminator settings for a while and settled on "Medium/Low" as this gave the best result. The ABE in PixInsight was done with the standard settings. Both processing done quite a good job of removing the gradients, so the results had to be stretched quite a lot to show what was hiding within the black background

The conclusion is after playing with the two of them for a while, I'm more confident in the ABE in PixInsight. I've used it straight "out of the box" without any additional settings, so I think there is much more power to be explored in these tools, especially since there is also a Dynamic Background Removal tool which I haven't even looked at yet!

EDIT: The finished image is here http://stargazerslounge.com/imaging-deep-sky/93949-twinkly-m45.html#post1345667

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Edited by Euan
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Putting aside the choices in processing software, why are you getting these serious gradients? Was this image shot on a Moonlit night or do you always get severe gradients like this regardless of the Moon's state?

That's a very good question which has bugged me for ages....

It seems to be my flats that are the problem. An uncalibrated images doesn't have the same effects, although it has all the vignetting and dust bunnies

I've tried so many different combinations of calibration:

  • Different exposure length flats in DSS, stacking on Average
  • Different exposure length flats in DSS, stacking on Median
  • Different exposure length flats in DSS, stacking on Sigma Clip
  • Different exposure length flats in MaximDL, stacking on Average with and without Boxcar Filter
  • Different exposure length flats in MaximDL, stacking on Median with and without Boxcar Filter

It drove me to the point of just finding the best comprimise, which was to calibrate in Maxim then stack in DSS, then deal with the gradients in processing

I might try some stacking in PixInsight and see what happens

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The system I have used is similar exposure length flats in MaximDL, stacking in Median with Boxcar Filter and this seems to work quite well. The following are before and after single light frames taken with my OSC camera. What light source are you using for your flats, twilight, reflection or emission? The 10 flats used here were taken using an electroluminescent screen (emission). These are my first foray into trying hard with flats and as you will see, there is still some tuning to be done but Gradient Xterminator did a good job of completing the task on the finished image.

201209-003ros_no_flat.jpg

201209-003ros_flat.jpg

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I take flats during the day (usually cloudy or course) with a few sheets of diffusing plastic over the scope.

I like the idea of the electroluminescent panel, then at least I could take them at night! Where did you get yours from or did you make one yourself?

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EL sheet is great for flats. SteveL put me onto the idea at Kelling. This is where Steve directed me EL Panels The cable into the sheet is a bit flimsy so I protected it with gaffer tape and sandwiched sandwiched the sheet between 2 sheets of snow white perspex. Works beuatifully.

Quick, easy and effective way to use gradient exterminaotr - make sure adjust background colour is selected when using on colour images, use the lasso tool to draw around the target then go into the select menu and invert the selection. Run GE with both setting on low.

That is only half the job. Next use the magic wand tool set on contiguous with a tolerance of around 10 (although this varies from image to image). Keep clicking until all the background has been selected. Then deselct any areas encroaching on the target, leave a small non selected border around the target. No use both settings on high. Readjust the black point and job done.

The only time I find problems is when the image is dominated by nebulosity.

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Hi

It looks like you have made a good start with pixinsight , eventhough I think you will find after a while you will not be using ABE as it is the quick and sometimes dirty method, DBE will give better results.

Even though gread x is a excellent program , DBE is more versatile :hello2:

If the problem is your flats can you see the error in your flats !

Some times the gradient show up better after flat fielding

Look at one of mine after perfect very good fielding

Harry

post-16736-133877417525_thumb.jpg

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