Step 9: Add A Levels Adjustment Layer

We're going to turn all that ugly noise into some stars, and we'll do that using a Levels adjustment. Now we could use a regular Levels image adjustment by going up to the Image menu at the top of the screen, choosing Adjustments, and then choosing Levels, but we don't want to do that. In fact, we almost never want to do that. And when I say "almost", I mean never, as in we never, ever want to do that.

The reason is because we would be making permanent changes to our image, and why make something permanent when you don't have to? Why not give yourself the freedom to go back anytime and make changes, without having to worry about harming the image in any way? You can give yourself that freedom in Photoshop by using adjustment layers, which are special layers that do the exact same thing as regular image adjustments, but without making any permanent changes to the image!

In this case, we're going to use a Levels adjustment layer. Hold down your Alt (Win) / Option (Mac) key and click on the New Adjustment Layer icon at the bottom of the Layers panel:

Select Levels from the list of adjustment layers that appears:

By holding down Alt (Win) / Option (Mac) as we select a Levels adjustment layer, we tell Photoshop to pop open the same New Layer dialog box we saw earlier before adding the layer. This time though, we're not going to bother naming the layer. We want to select one of the other options in the dialog box. Directly below the Name option at the top, you'll find an option called Use Previous Layer As Clipping Mask. By selecting this option, any adjustments we make in the Levels dialog box will affect only the layer directly below it (our Stars layer). The original image on the Background layer will not be affected. Click inside the checkbox to select the option, then click OK to close out of it:

Step 10: Reduce The Amount Of Visible Noise To Create The Stars

If you're using Photoshop CS4 or higher, the options for the Levels adjustment layer will appear inside the Adjustments Panel which was new in CS4. In CS3 and earlier, a separate Levels dialog box will appear. The most prominent feature in Levels is the histogram, a black graph resembling a mountain range which shows us the current tonal range of the image, or in our case, of the layer directly below the adjustment layer (the Stars layer). Below the histogram are three small sliders - a black one on the left, a white one on the right and a gray one in the middle. Normally, we use these sliders to adjust the contrast in an image, but in this case, we're simply going to use them to reduce the amount of noise we're seeing on our Stars layer so that what we're left with looks more like, well, stars!

First, click on the white slider and drag it a little towards the left. As you drag, you'll see the noise in the image becoming brighter. You won't need to drag this slider very far. Just drag it enough to brighten the noise a little. Then click on the black slider and begin dragging it towards the right. As you drag this slider, you'll see the darkest areas of noise begin to fade away, and as you continue dragging towards the right, more and more of the noise will fade away. Continue dragging the black slider to the right until so much of the noise has disappeared that all you're left with is a few random dots scattered around in the sky. These are the stars!

Here's what my sliders look like. Notice how the white slider was dragged only a short distance to the left, but the black slider needed to be dragged far over to the right in order to remove most of the noise from the image (the middle gray slider will move on its own as you drag the white and black sliders):

You'll probably need to go back and forth a little with the two sliders until you're happy with the results. In Photoshop CS3 and earlier, click OK when you're done to close out of the Levels dialog box. In CS4 and higher, there's no need to close out of the Adjustments Panel. Here's my image after removing most of the noise and creating my stars:

If you decide you're not quite as happy as you thought you were with how the stars look and you want to fine-tune them some more, you can easily do that thanks to the power of adjustment layers! If we look in the Layers panel, we can see our Levels adjustment layer, named Levels 1, sitting above the Stars layer:

To get back to the Levels options at any time and make changes to the sliders, in Photoshop CS4 or higher, simply click on the Levels thumbnail to display the Levels options once again in the Adjustments Panel. In Photoshop CS3 and earlier, double-click on the Levels thumbnail to re-open the Levels dialog box. In either case, make the changes you need to the sliders, then click OK to close out of the Levels dialog box (Photoshop CS3 and earlier), or just leave the Adjustments Panel open (CS4 and higher):

I'm happy with the number of stars I have in my image, so I'll leave my Levels sliders alone. The only thing I'm not happy with at the moment is that the effect looks very fake because the lighting is wrong. The original photo had a nice warm glow rising into the sky from all the city lights, but at the moment, that glow is missing. It looks more like the city was cut and pasted in front of the stars. Let's quickly bring back the warm glow, and we'll do that next!