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I need help with an image of stars.


DichoMire

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Hello everyone,

I am trying to make a background for a website and I really liked the idea of making an image of space where the stars move relative to the mouse position. I have an idea how to make it - have one background and 3-5 images with a different set of stars in each, which are layered upon each other.
So I decided to work on this image:
wallpaperbetter.com_1920x1200.jpg
I made a copy with just the background:
cleared.png
And I made a copy that has all of the stars:
stars.png
The problem is, I don't know how to separate the stars into 3-5 layers. If I do it manually, I fear that they will be grouped into small clusters and it wouldn't look believable.
So I came up with the idea to make a selection of random pixels, use some kind of feathering maybe to add the whole stars to the selection, then split them into different layers.
So I tried out this tutorial:
Which makes use of noise to make a random selection, but the noise made too big of a selection, so I'm not sure it will work.

Do you have any ideas? I am willing to try anything out, even if it is time consuming.
 

Rich54

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Not sure of your level of Photoshop skills, but I have two possible ideas:
  1. Create a random selection by using a custom brush with the brush dynamics set for size jitter and scatter.
  2. Use the Blend-If sliders to select different luminosities of stars

Method1
You can use any existing brush or you can create a custom brush of any shape you like. The red dots below are a custom brush I made long ago. By setting the shape dynamics and the scattering, you can quickly spread these shapes over a large area in a random, yet controlled way, and then use the result as a selection for a layer mask. (The red dots need to be on their own layer.)

1616539657830.png

Here's what it looks like on your star image. With scattering, it took me five seconds to make this. Once you've created selection #1 from this, you can copy the red dots to a new layer and move them or rotate them to create selection #2, etc.

1616539956125.png


Method2
  • Copy your original composite image to a new layer.
  • Below the new layer you've just created, insert a new layer filled with black.
  • On your top layer, open the Layer Styles window and go to the Blend-If sliders. Depending on the settings (where the red arrow is pointing), you can select different stars based on their relative luminosity. Experiment with different settings to create four or five different selections. Here's an example:
1616540709505.png
 

DichoMire

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Method 2 sounds great. Unfortunately for this case it doesn't work :p.
It selects space around previous selections:
b9bdad03632122fcf65cdceac120548a.png
That is unfortunate because I really liked the method. It made sense to group similarly luminous objects in the same layer.

I did have more luck with Method 1.
I managed to make a scattering selection:
16ee92e8bdb102b4c0f89dccd7b994e2.png
This is an older picture. I fixed the hardness of the brush later on.

I do have another difficulty now, though:
I would like to take the random selection above and subtract all of the empty space from it. I tried using magic wand with ALT click:
2021-03-24 19_30_46-starmap2.psd @ 400% (Layer 1, RGB_8) _.png
But for some reason that added new stars to the selection.
2021-03-24 19_31_40-starmap2.psd @ 400% (Layer 1, RGB_8) _.png
Is there a tool in photoshop that allows selecting the intersection between two selections? In this case, the selection I made above and the inverse of the whitespace? I read you can use Shift + Alt to make intersection between for example Lasoo and a Rect select. I have my two selections which I want to intersect in the Channels tab.

Thanks for helping me out, I really appreciate it! I couldn't respond earlier because I BSOD'ed.
 

Rich54

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I think you're trying to do too many things at once. The first step is to isolate all the stars from the background. In your original post, you already have a PNG file called Stars where you somehow isolated all the stars onto a white background (I'm curious how you did that), except that the stars are dark and the background is white. Here's what I would do:
  • Invert your Stars file (Ctrl+i) so that the stars are white and the background is black.
  • Duplicate that layer and add a Threshold adjustment layer above it. Set the threshold slider all the way to the left, at Level 1.
  • Merge the Threshold layer with the layer immediately below it.
  • Using the magic wand, select everything that's black (i.e. not a star) and hit delete. This leaves you with a layer that is pure stars and nothing else.
  • Make a selection of the stars from this layer and apply it to your original bottom layer, which does not have the threshold adjustment. Either delete the black background from your original layer or use a layer mask. This layer is now your master file of Stars Only.
I believe the next step is that you want to somehow carve-up the stars into four or five different views based on a random selection or on a luminosity selection. Once you have the Stars Only layer, I think any of the methods we tried above will work. Or, you can just use the Lasso tool to make your own selections by hand. Let me know if this works.

To answer your specific question about selections, the Lasso tool and the rectangular marquee tool have controls that allow you to select the intersection of two selections. I have an old version of Photoshop so these icons may have moved, but you need to select the one where the red arrow is pointing.

1616615611061.png
 

DichoMire

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I actually already had the stars isolated. I used Select -> Colour Range. Highlights didn't select nearly enough stars, so I picked Midtones and played around with the fuzziness and the Range until I was satisfied with the selection. I then made a new file and pasted them there, that is why there is a white background. It was easier to see what selection I've made, as the stars blended in with the transparent background.

Unfortunately I had to reset my computer, so I'm glad I made this post and put the images up here. I followed your steps and I once again have the stars selection. I didn't know about the Lassoo and Rect Marquee tools' intersections, though I'm not sure that willbe of much help in this case.

I did however figure out an alternative method:
1) I did the rendom selection on the quick mask mode with a scattered brush as you suggested.pic1.png
2) After going back into regular mode, I go into Select -> Grow, which for some adds everything but the star parts I had in the random selection in the current selection.pic2.png
3) So I invert selection and then once again I do Select -> Grow, which adds neighbouring similar cells to star parts that were in the random selection.pic3.png
And then that's one of the layers done. I just repeat the steps.
Can't say I quite understand how the Grow function works, but hey, it does the job :D .

Thank you very much Rich54 for the assistance!
 

Rich54

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Glad I could help. I'm not familiar with Select>Grow because I have an old version of Photoshop. I have Select>Modify>Expand, which sounds like it might be similar.
 

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