historgraph modification on only one zone

Software Siril
1

Hello,

Is it possible to apply historgraph modification to an image, but only in a selected area?
I am working on an image, and I need a different stretching in an area with a bright object than in another area with a fait object. Is that possible?

Thanks,
Cyrille

2

Hello.

No it isn’t. But Generalized Hyperbolic Stretch is very powerful is dedicated to work on area with different lightness.

3

Hello,

Thanks, I will give it a try… Looks like they are lots of cursors and options :slight_smile:
Standard historgram is so much simpler… click on the “Auto”, move one or 2 cursor and your are done :slight_smile:
I am but an absolute beginner here… so I need to learn.

Thanks,
Cyrille
P.S. I am working an an M57 picture and I want to not-burn the nebula, BUT also show the mag 15 NGC galaxy (elongated spiral) which is next to it (and I also spotted another smaller galaxy on the other side)…

4

And this is why we have a very good tutorial for that: Siril - Generalized Hyperbolic Stretch (GHS) Transformations

5

Hello,

And in addition, it is a REAL tutorial, not some bad youtube vidéo!
Thanks for the great work on siril and documentation.

Cyrille

6

As an idea, this can be solved with mask and pixel math.
For example:

  1. Divide channels into R, G, B
  2. Make a mask
  3. Compose an image from the mask and R, G, B in pixel math.
  4. GHT the masked image (step 3)
  5. Compose the original image and GHT using pixel math.

For information

7

Hello,

This is a nice trick! Thanks for the pointer…
I ended up using paint.net to compose… but blending is also an issue I am discovering :frowning:

Cyrille

8

I really recommend to use GHS and not mask in a first time.