local saturation modification

[gnnyman]

Hi everyone,

I am new to GIMP and would like to use it in future instead of the expensive Adobe PS. One of my important do´s is to alter the saturation of  part of an image. I am astrophotographer and as example want/need to increase or decrease the saturation of a nebula or part of it, but not of the entire image. In PS, I choose the respective icon and see three options - darken, lighten and saturation. Inside of those, I can select shadows, midtones or lights for darken/lighten and for saturation increase/decrease.
In GIMP, I have found the options like in PS but only for lighten/darken using a brush not for saturation.

Where is this function hidden? What do I need to look for?

I have attached an image of the NGC224, the Rosetta Nebula as an example of what I do.

Thanks and greetings from Austria,

Georg

[zeuspaul]

Using the Free Select tool (or other selection tool) trace the area you want to change.  Close the selection by clicking on the first point.

In the color drop down menu choose saturation or any other modifier.  The changes will be to the current selection.

[Krikor]

I suggest testing these two options:

satmaskLCH_multi.py - https://gimplearn.net/viewtopic.php?p=37764#p37764

saturation_h_m_l.py - https://gimplearn.net/viewtopic.php?p=38326#p38326

[gnnyman]

(02-20-2022, 08:02 AM)zeuspaul Wrote: Using the Free Select tool (or other selection tool) trace the area you want to change.  Close the selection by clicking on the first point.

In the color drop down menu choose saturation or any other modifier.  The changes will be to the current selection.

Thank you for your advice - it means I need to use a masked selection. This is often not very handy because as you can see, some of the areas have no discrete boundaries and with PS and a soft brush I can "paint" over those areas with a small amount of intensity, e.g.10%. and thus increase or decrease the local saturation. What I would like to have here as well is an adjustable brush (diameter, intensity, hardness etc) to alter the saturation....

Rgds
Georg

---

(02-20-2022, 09:22 AM)Krikor Wrote: I suggest testing these two options:

satmaskLCH_multi.py - https://gimplearn.net/viewtopic.php?p=37764#p37764

saturation_h_m_l.py - https://gimplearn.net/viewtopic.php?p=38326#p38326

Thank you for your advice - it means I need to use a masked selection. This is often not very handy because as you can see, some of the areas have no discrete boundaries and with PS and a soft brush I can "paint" over those areas with a small amount of intensity, e.g.10%. and thus increase or decrease the local saturation. What I would like to have here as well is an adjustable brush (diameter, intensity, hardness etc) to alter the saturation....

Rgds
Georg

[rich2005]

Is it not the brush in `HSV Saturation' mode / fuzzy brush / low opacity ?

like this https://i.imgur.com/HmxOde4.mp4

[gnnyman]

(02-20-2022, 11:05 AM)rich2005 Wrote: Is it not the brush in `HSV Saturation' mode / fuzzy brush / low opacity ?

like this https://i.imgur.com/HmxOde4.mp4

Oh....yes, sure...I overlooked this completely.....I shall try it - thank you very much for showing me how it works!,

regards.


Georg

[gnnyman]

(02-20-2022, 11:05 AM)rich2005 Wrote: Is it not the brush in `HSV Saturation' mode / fuzzy brush / low opacity ?

like this https://i.imgur.com/HmxOde4.mp4

Thanks again, but I tried it and desaturates only - it also says that it is desaturation - where I can do the opposite - saturate more. You short tutorial also shows desaturation not saturation increase...

regards

Georg

[rich2005]

Similar set up: Try HSV Value mode Does get get what you require ?

[gnnyman]

(02-20-2022, 04:09 PM)rich2005 Wrote: Similar set up: Try HSV Value mode Does get get what you require ?

I tried and yes, it does the trick.... now I have to learn how to get rid of the RGGB caused green overcast in an FITS image. You know, when you stack images coming from an astrocolor camera (RGGB matrix or whatever system or R,G and B) - there are two green channels, which results in a totally green raw image. I have ordered a newly released GIMP book and shall study it...

Regards

Georg

PS: Thanks for your help and feedback!

[rich2005]

There is a bit of astronomy interest on the https://discuss.pixls.us/ forum. You could try questions there.

What is the "newly released GIMP book" the ones I know are all ancient