Help with blending 2 pictures together in photoshop

[beamer3.6m]

I use Photoshop CS2 because I have it and I dont want to pay for the monthly CC versions.

I often see reference to processing an image without stars so I use Starnett++ to remove them. My question is, once I have processed the images (one with stars and one without) how do I merge/blend (or whatever you call it) back together.

Ive searched Google and watched tutorials but it just is not going in. I dont understand layers or how to work on them or set them up or anything really.

I NEED AN IDIOTS GUIDE. Can anyone help me in simple 1, 2, 3 like steps??

This is the best I can get with my processing skills. I just do not understand photoshop at all... 

Compared to my initial processing attempt:

Edited October 4, 2022 by beamer3.6m

[raadoo]

Here's a step by step that will hopefully this will clear things up:

1. Split your stars and background into two images
2. Use Photoshop's File > Scripts > Load Files Into Stack script to load the two images
3. Once you hit OK in the script dialog you should have the two images loaded as individual layers
4. Make sure the image of the stars is the layer above the background
5. Change the stars layer blending mode to Screen

I've attached a few screenshots of what these look like.

[woldsman]

The basic idea is to create a starless image - which you have done using Starnet++. You then load the starless image and the original image as layers. Next you subtract the top image (which should be the starless image) from the bottom one . Now you have a stars only image. Finally, you load the starless image and the stars only image. You add the top image to the bottom one.

You can use Gimp for the above processes. Load the images as layers. After subtracting or adding, go to the images tab and click “merge visible layers” then export the merged image.  
 

Images should be aligned for subtraction or addition. You may want to work separately on an image that is going to result in a starless nebula and also an image that is going to result in stars only. In this case, align at the stacking stage and make sure any crops are the same dimensions. 
 

Your M45 looks good btw!

 

[beamer3.6m]

15 hours ago, woldsman said:

The basic idea is to create a starless image - which you have done using Starnet++. You then load the starless image and the original image as layers. Next you subtract the top image (which should be the starless image) from the bottom one . Now you have a stars only image. Finally, you load the starless image and the stars only image. You add the top image to the bottom one.

You can use Gimp for the above processes. Load the images as layers. After subtracting or adding, go to the images tab and click “merge visible layers” then export the merged image.  
 

Images should be aligned for subtraction or addition. You may want to work separately on an image that is going to result in a starless nebula and also an image that is going to result in stars only. In this case, align at the stacking stage and make sure any crops are the same dimensions. 
 

Your M45 looks good btw!

 

This is all a bit complicated to take in... how do you subtract one image from another for example...

It's SO complicated a photoshop is not intuitive at all.

[beamer3.6m]

16 hours ago, raadoo said:

Here's a step by step that will hopefully this will clear things up:

1. Split your stars and background into two images
2. Use Photoshop's File > Scripts > Load Files Into Stack script to load the two images
3. Once you hit OK in the script dialog you should have the two images loaded as individual layers
4. Make sure the image of the stars is the layer above the background
5. Change the stars layer blending mode to Screen

I've attached a few screenshots of what these look like.

Brilliant, I will try this...

[carastro]

@beamer3.6m

If you are finding Photoshop difficult, particularly layers, I have a number of video tutorials on Youtube which you might find helpful.  In particular I have a tutorial called understanding layers.

See my web page for links:

https://sites.google.com/view/astrophotography-carole-pope/video-tutorials?authuser=0

Carole 

 

[ollypenrice]

I've been experimenting with all sorts of ways of recombining extracted stars after de-starring  and have concluded that the best method is the one outlined by Xiga in the link below. However, I think you also need to think about when, in the processing, you extract the stars.  If you leave it too late you'll have the problem that they are already too big and will need reverse-processing. So far, I'm favouring a partial stretch to the point at which the stars are about where I want them to be at the end. At this point I remove them and continue to push the starless stretching as hard as I can. I then follow the method in the link, giving a tweak in Curves if necessary. I never expect anything in processing to be formulaic. Every step also needs a bit of thought.

The key point is that there is no point in removing the stars and then putting the same ones back! At the moment I'm favouring a fairly early removal, a continued stretch of the starless and then a replacement.

 

Edited October 11, 2022 by ollypenrice
clarification

[AstroNebulee]

What I do is:

Create my starless image with starnett++2 and process that.

Then on a separate tab. I do a slight stretch of my stars (original image) just to bring the stars out a tad more without blowing them out. 

Go to the starless image tab and choose select-all, then copy. 

Go to the stars image tab and make sure to the top layer is selected and press-edit - paste. This should paste the starless image on top and you should see only the starless image now. 

Go to the blending mode box and select screen, this should merge both together. You can use the opacity slider to suit to taste. 

Lee 

Edited October 11, 2022 by AstroNebulee