Put highlights and shadows on different layers

[kenh000]

Hi.

I am currently evaluating Affinity Photo to use with Astrophotography.  I was hoping someone could help me with some basic questions.

Imagine a photo of the night sky. A few stars but mostly 'dark sky'.  The dark sky is far from black due to light pollution and other effects and often has a reddish or other color hue to it. To put it in terms of RGB think something like R: 90, G: 75, B: 78. I want to neutralize and darken the sky - something like R: 35, G: 35, B:35. I know how to do this in Photoshop (use the black point adjustment tool in Curves) but from poking around in the software and forums that feature is not yet available in AP. If I try to adjust the RGB values for the entire image, the stars also get impacted. So, how would I go about doing this in AP? My thought is to create a layer with just the stars on it and another layer with just the sky background. I could then manipulate the RGB values of the sky layer without impacting the star and then re-merge the layers. I have no idea how to select the stars and put on a layer and select the sky to put on another layer. How do I do these things in AP? Does any one have a better suggestion on how to accomplish this?

Thanks.

Ken

[h_d]

Hi and welcome!

I've only tried this with an "artificial" sky field set to your colour spec (R90 G75 B78), but a Brightness and Contrast adjustment layer with the blend mode set to Colour Burn may do the trick:

 

I suspect there are lots of other ways...

 

 

[smadell]

The easiest way I can think of is by using Luminosity masking, or by fiddling with the Blend Options directly. In brief, you can take your dark-sky-and-stars layer, duplicate it, and use Blend Options (click the Gear icon at the top of the Layers panel) to limit each of these layers to the dark areas or the light areas, respectively.

[walt.farrell]

Welcome to the Serif Affinity forum, Ken.

It would help to have a sample image. You should be able to attach a PNG image to another post so we have something to experiment with. But you can adjust the black point, though it's done differently than with PS. And this has been discussed at least once before. Perhaps something here will help, as it shows the use of Curves or Levels in an astrophotography context in AP:

The AP Help for the Levels Adjustment also has some useful information.