Simple removal of gradients and vignetting

[Fo_Cuss]

Gimp Version (does a better job IMHO)

Below are :

Original Image .... PixInsight Modded Image
Gimp Modded Image (exact details) .... Gimp Colour Enhanced Image

Note
The PixInsight stars are not the same colour as the original (and colours are washed out).
The 1st Gimped image has extracted the exact colour details from the original image.
The 2nd Gimped image lifts the original colours (as an option if wished)

Do appreciate that I figured this method by myself ... I'm sure it can be improved.

The most important element, is that Gimp enables accurate extraction of the detail, with the option of colour enhancement
... and it doesn't cost a penny.

However, it is thanks to Rikyuu's original work, that guided me to this method 👍

I suggest that I write up the method as a separate tutorial.
Whether it should be stuck is up to the admins
... but as the original LE software is no longer available, and Gimp will be free and with us forever....

🌝

[Jm1973]

On 01/01/2020 at 20:50, Fo_Cuss said:

Gimp Version (does a better job IMHO)

Below are :

Original Image .... PixInsight Modded Image
Gimp Modded Image (exact details) .... Gimp Colour Enhanced Image

Note
The PixInsight stars are not the same colour as the original (and colours are washed out).
The 1st Gimped image has extracted the exact colour details from the original image.
The 2nd Gimped image lifts the original colours (as an option if wished)

Do appreciate that I figured this method by myself ... I'm sure it can be improved.

The most important element, is that Gimp enables accurate extraction of the detail, with the option of colour enhancement
... and it doesn't cost a penny.

However, it is thanks to Rikyuu's original work, that guided me to this method 👍

I suggest that I write up the method as a separate tutorial.
Whether it should be stuck is up to the admins
... but as the original LE software is no longer available, and Gimp will be free and with us forever....

🌝

Hi. Did you ever write up any instructions on how to do this in GIMP please?

[alan potts]

Don't know why but my computer will not allow me to go to that site,

Alan

[Xsubmariner]

The original thread is 2009 so I suspect the site no longer exists.

Martin

[ollypenrice]

The GIMP-flattened image may have been black-clipped by the operation. It's hard to tell but it's something I'd be looking out for if I were to use it (which is unlikely since I have PI's DBE and ABE available and think they are the pick of the bunch.)

The image also has a considerable gradient and is very blue, an imbalance not confined to the background but also visible in the fainter stars. This image would not stretch well.

Olly

Edited September 24, 2022 by ollypenrice
Clarification

[vlaiv]

I just love these discussions over such long periods - maybe I'll have to wait a few years for any sort of reply/feedback

Here is simple tutorial how to do such background removal in gimp:

Open original image / convert it into 32bit float per channel:

Next use Filters /  G'Mic Qt

Select details:

and under details - select wavelet decomposition:

Select number of layers so that last layer is nice background (say 7 in this case)

This will create 7 layers:

Last one is called residual - make a copy of that layer

Select all layers except that copy and merge them back to single layer (use merge visible layer by setting all visible except copy - set it to not visible, move residual on top as well):

Finally, set mode of that residual to subtract:

Here is result:

This will result in some clipping of the black - in order to avoid that, increase brightness of original layer or decrease brightness of residual layer by tiny bit.

Here is image and histogram after increasing brightness a bit:

 

[Karl Perera]

We seem to have no shortage of ways to remove gradients and vignetting especially it seems that there is a button for everything in Pixsinsight. I use Photoshop and suggest a few different alternatives that I use:

• Remove gradients by using GadientXterminator
• Remove gradient by using filter - blur -average and subtract this from your image. 
• Use AstroFlat Pro it's cheap and works nicely to flattern image and take away gradient
• Mask the nebula using color range and then remove colors from background
• Vignetting can easily be removed or adjusted by using camera raw filter adjustment for vignetting
• Vignetting is also taken care of in the abovementioned AstroFlat pro software
• Any other ideas? 

[kirkster501]

There isn't a "button for everything" in PI.  it is true that Russell Croman has recently introduced some scripts and modules that can help but a great deal of skill and experience is still needed to process a load of subs into a final image.  To say nothing of collecting the data in the first place.

[AstroMuni]

On 24/09/2022 at 14:25, vlaiv said:

maybe I'll have to wait a few years for any sort of reply/feedback

And by then there will be a few more software out there that do a better job 😉

[AstroMuni]

16 minutes ago, Karl Perera said:

Any other ideas? 

Siril has a tool based on GraXpert

[ONIKKINEN]

4 hours ago, AstroMuni said:

Siril has a tool based on GraXpert

Great tool, so far have not found a gradient it could not deal with. IMO better than DBE in PixInsight too, but that is most likely user error as have not had time to learn DBE as well as possible.

[Karl Perera]

Lots of ways to remove gradient that are quick and easy including:

• In Photshop, click Filter then Blur select Average. Apply image and subtract from the current image layer.
• Use RC-astro gradient Xterminator
• Use astroflat pro
• vignetting control in camera raw filter 

this is all with Photoshop. Hope this is of some help.