AstroBin

AstroBin

AstroBin

DBE Pleiades Astrophoto PixInsight · dkamen · ... · 6 · 1039 · 0

dkamen 7.44
dkamen
...
· 
·  1 like
·  Share link
Hi guys,

I did DBE with subtractive correction on a linear image with signal level ~0.002 and noticed the result had signal levels around 0.30, practically stretched. How is that mathematically possible?

Thanks,
Dimitris
Like
×

Sorry :-(

Editing a post is only allowed within 24 hours after creating it.
×

Share this forum post

Copy the URL below to share a direct link to this post.

Close
×

Post editing not available

This post cannot be edited using the classic forums editor.

To edit this post, please enable the "New forums experience" in your settings.

Go to Settings Close
mxpwr 7.29
D. Jung
...
· 
·  1 like
·  Share link
Mathematically speaking? By subtracting a negative background smile
Joke side, did you enable the rescaling/normalization option in the DBE process? That might be a the root cause for your observation.
Edited ...
Like
×

Sorry :-(

Editing a post is only allowed within 24 hours after creating it.
×

Share this forum post

Copy the URL below to share a direct link to this post.

Close
×

Post editing not available

This post cannot be edited using the classic forums editor.

To edit this post, please enable the "New forums experience" in your settings.

Go to Settings Close
andreatax 9.89
andrea tasselli
...
· 
·  Share link
As far as I remember PI only deals with positive numbers so that value seems to be odd.
Like
×

Sorry :-(

Editing a post is only allowed within 24 hours after creating it.
×

Share this forum post

Copy the URL below to share a direct link to this post.

Close
×

Post editing not available

This post cannot be edited using the classic forums editor.

To edit this post, please enable the "New forums experience" in your settings.

Go to Settings Close
CWTauri 22.98
Adam Block
...
· 
·  6 likes
·  Share link
I think you are taking the semantic meaning of the method "Subtraction" too literally. A gradient correction will fit the background both adding and subtracting values based on the samples and other configured parameters. An additive undesired gradient, yes, will generally be subtracted which is why the method was given this name (I think) because of its practical benefit. However, the correction of a gradient will add or subtract as necessary to make it uniform. Furthermore, if you place samples on dark regions.. DBE will attempt to add values there… and if they are very small and you have not constrained DBE..the result can be quite bright. 

In fact, as I demonstrate in my videos on DBE, you can actually change the value that is added or subtracted in an area by changing the calculate brightness value at any sample. 
Did you ever notice that DBE will sometimes make bright objects have a dark background near them? So people avoid putting samples there..but that isn't enough sometimes… so you can manually adjust the brightness of model (add or subtract) to clean this up.

If you are interested in explanations and demonstrations as I have described above… please become a member of my site at AdamBlockStudios.com . You will find it very informative.

-adam
Like
×

Sorry :-(

Editing a post is only allowed within 24 hours after creating it.
×

Share this forum post

Copy the URL below to share a direct link to this post.

Close
×

Post editing not available

This post cannot be edited using the classic forums editor.

To edit this post, please enable the "New forums experience" in your settings.

Go to Settings Close
jrista 11.18
Jon Rista
...
· 
·  Share link
Hi guys,

I did DBE with subtractive correction on a linear image with signal level ~0.002 and noticed the result had signal levels around 0.30, practically stretched. How is that mathematically possible?

Thanks,
Dimitris

What settings did you use? DBE has a normalization option that will attempt to restore the original offset level after extraction. This is disabled by default, which can result in unexpected results sometimes. Usually it results in the image becoming much darker, requiring re-application of STF, however as Adam mentioned, it depends a lot on exactly how you have sampled the image. Sometimes the nature of your sampling and the exact modelization of your gradient will shift the signal when the Normalize option is NOT enabled. 

Try enabling normalization, and see if this helps.
Like
×

Sorry :-(

Editing a post is only allowed within 24 hours after creating it.
×

Share this forum post

Copy the URL below to share a direct link to this post.

Close
×

Post editing not available

This post cannot be edited using the classic forums editor.

To edit this post, please enable the "New forums experience" in your settings.

Go to Settings Close
dkamen 7.44
dkamen
Topic starter
...
· 
·  Share link
Update: I cannot replicate it. I mean I opened the same image, did DBE again, this time the result is normal. 

I am 100% certain I didn't have normalize selected, or division, or anything like that. Because I never use those things. Maybe Pixinsight just threw a fit, sometimes it happens, especially with dynamic processes. 

Thank you for your replies.

Cheers,
D.
Like
×

Sorry :-(

Editing a post is only allowed within 24 hours after creating it.
×

Share this forum post

Copy the URL below to share a direct link to this post.

Close
×

Post editing not available

This post cannot be edited using the classic forums editor.

To edit this post, please enable the "New forums experience" in your settings.

Go to Settings Close
ajitheverester 0.00
Ajith Everester
...
· 
·  Share link
andrea tasselli:
As far as I remember PI only deals with positive numbers so that value seems to be odd.

Like
×

Sorry :-(

Editing a post is only allowed within 24 hours after creating it.
×

Share this forum post

Copy the URL below to share a direct link to this post.

Close
×

Post editing not available

This post cannot be edited using the classic forums editor.

To edit this post, please enable the "New forums experience" in your settings.

Go to Settings Close
 
Register or login to create to post a reply.
×

Warning!

This operation will reload the current page. If you have any unsaved information in a form, it will be lost.

You can also dismiss this window, and your operation will be applied at the next page navigation.