DBE Problem

[ashworthacca]

Hi guys, I have a problem everytime I used Dynamic backgound Extraction in Pixinsight. Every image that I want to correct vignetting problems I always get red crosses on the problem areas when I'm selecting samples.


DBE Problem by ashworthacca, on Flickr

 in Model parameters (1) I have increased the Tolerance value from 0.5 > 0.9 but still didn't work.


DBE Problem 1 by ashworthacca, on Flickr

Any ideas guys as it happens on every image with vignetting problems.....I need to take better flats.

[Ioannis Ioannou]

You have to experiment with model parameters until you are satisfied with the samples.
In your case for example, I would had increased Shadow relaxation (and then re-generate the samples)

[sreilly]

I can't really tell from the scale of the image but if you select any of the red x's, does the square to the right turn black? I'm thinking that there are stars under those red x's and I'd try shifting them by dragging them slightly and see if that turns them white. Other than that, I have no idea what may be causing this.

[Nocturnal]

What this generally means is that the red samples lie outside the predicted background model. Hover over the 'tolerance' parameter and read the tooltip. Try increasing the tolerance.

[ashworthacca]

Thanks guys, I tried all your suggestions and finally managed to get it to work by increasing the tolerance way up to 5.5 (before I didn't go any higher than 0.9 as I didn't think that you should  )

Anyway, the vignetting was eliminated so many thanks again guys, much appreciated.

Regards
Martin

[Nocturnal]

5.5 is very high. Did you not flatten this image? Remember DBE is generally used to remove additive gradients, not multiplicative vignetting.

[ashworthacca]

5.5 is very high. Did you not flatten this image? Remember DBE is generally used to remove additive gradients, not multiplicative vignetting.

I'm not sure what you mean but heres what I did.

Stacked in Nebulosity V2 and did the initial Digital Development Stretch in Nebulosity V2. Saved the file as a fit file. Opened it in Pixinsight, ran Background Neutralization then DBE.

[Nocturnal]

You should understand this part "did you not flatten this image". If you don't then please describe in more detail how you stacked in Nebulosity. In addition you should not do DDP in Nebulosity *at all* if you have PixInsight but besides that DBE works best with linear images. After DDP the image is no longer linear.

[harist]

If you haven't done so already you should check Harry's video tutorials

http://www.harrysastroshed.com/pixinsighthome.html

Tasos

[ashworthacca]

You should understand this part "did you not flatten this image". If you don't then please describe in more detail how you stacked in Nebulosity. In addition you should not do DDP in Nebulosity *at all* if you have PixInsight but besides that DBE works best with linear images. After DDP the image is no longer linear.

Sorry, with reference to Nebulosity I don't understand what  "did you not flatten this image" means. I have never seen this option mentioned in the software.....unless its the "Save Stack" option??

First thing I did was align and combine my darks and flats.  Then Preprocess B&W/RAW with my master Darks/Flats. Then did a Batch Demosaic + Square of the preprocessed lights. Finally did the align and combine of the lights from the previous process. Checked "save stack", used Translation as Alignment method and checked "Adaptive scale stack to 16 bits".

Saved the result as a fits file, did the Digital Development and saved. Opened up in Pix, Background Neut the DBE.

I know I don't haver to do Digital Development but I was testing something out in this particular case. The DBE issue happened after stcking with DeepSkyStacker as well with no processing whatsoever.

Thanks for taking the time to help.......setting the tolerance up so high goes against everything that I have read.

[ashworthacca]

If you haven't done so already you should check Harry's video tutorials

http://www.harrysastroshed.com/pixinsighthome.html

Tasos

Thanks Tasos, I have them all on DVD and have been through them all.......I think I need to revisit the DBE one.

[harist]

Yep, the DBE one is very informative.

Tasos