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Create a Diffraction Spike Brush for Photoshop
Submitted: Thursday, 27th September 2007 by Al Sheehan

Diffraction spikes. Some people love them, others hate them. Some people think they add to the aesthetics of a stellar image, and others just see them as an artefact. But those who like the aesthetic effect of diffraction spikes sometime go to great lengths to create them in their images.

Photoshop can also be used to add diffraction spikes to your images. This article describes how to make your own Diffraction Spike brush for Photoshop, so you can add artificial diffraction spikes to your images. You can if you want also create a range of different diffraction spike brushes so you can have long, fine spikes or shorter ones – its really up to you.

Photoshop CS3 was used to develop this article, but it doesn’t matter what version of Photoshop you have, you should be able to follow this method.

Create a New File

Start by opening Photoshop and making your foreground colour white, and the background colour black.

Create a new file: File, New. Make the new image 10cm x 10cm. This will help you to find the centre of the image, and select Background Colour for the Background Contents.

If the rulers are not displayed along the side of the image, select View, Rulers (or press Ctrl R) to turn them on.

Draw a Line

We will start to construct out diffraction spike brush by drawing a horizontal line through the middle of the image. Before we do, select the Zoom Tool, and zoom in to 200%. This will make accuracy when drawing easier.

Select the Line Tool (refer to Figure 1). Click on the Info Tab on the right hand side of the screen – this will help you to see accurately where the cursor is in the image to help get the line straight. Now draw a line from X=4.00, Y=5.00 to X=6.00, Y=5.00. The image should now look like Figure 1 with a white line 2cm long through the middle of the image.

Figure1.jpg

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Figure 1

Blur It

The line looks pretty harsh, and not much like a diffraction spike. To “taper” it and fade it at the ends so it looks like a diffraction spike, we will use the Motion Blur Filter: Filter, Blur, Motion Blur. A dialog box will appear. Set the Angle to 0° and, with the Preview box checked, play around with the Distance parameter to get the effect you like. I chose 100 in this case. You should end up with something like Figure 2.

Figure2.jpg

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Figure 2

Make a Cross

Let’s now turn this line into a crossed set of diffraction spikes.

Before we do though, notice that in the Layers panel (bottom right hand side of Figure 2) that we have 2 layers: Background and Shape 1. Merge them into the one layer by selecting Layer, Flatten Image from the menu.

Next, make a copy of the background layer: Layer, Duplicate Layer. Your screen should now look like Figure 3. Notice we now have two layers again: Background and Background copy.

With the Background copy layer selected, from the menu Select, All and then Edit, Cut. We now have a copy of the line in the clipboard.

Rotate the image 90° clockwise or anti-clockwise (Image, Rotate Canvas, 90° cw) and paste back the image from the clipboard (Edit, Paste). Finally, in the Layers panel on the bottom right hand side, adjust the opacity of the Background copy layer to 50%. Your screen should now look like Figure 4, and hopefully your image will look something like some diffraction spikes!

Figure3.jpgFigure4.jpg

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Figure 3

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Figure 4

Make a Photoshop Brush Preset

To make our image into a Brush Preset, let’s firstly flatten it i.e. get rid of the layers but keep the image: Layer, Flatten Image.

Next we want to invert the image as the black areas in the brush preset represent the brush shape: Image, Adjustments, Invert (or Ctrl I). See Figure 5.

Now to make it into a Brush Preset: Edit, Define Brush Preset… and in the dialog box, give your diffraction spike brush a name.

You new Diffraction Spike brush will appear at the end of the brush presets as in Figure 6.

Figure5.jpgFigure6.jpg

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Figure 5

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Figure 6

How to use your Diffraction Spike Brush

Use the brush by positioning it over the star you want to add spikes to and then click the mouse button. You can adjust the size of the spikes by adjusting the size of the brush either using the ] key to increase size and the [ key to reduce the size or from the Master Diameter control.

As we have created the brush here, the brush will have an inherent opacity of 50%, so even with the opacity of the brush selected at 100%, a set of white diffraction spikes on a black background will only give spikes that are 50% white. Clicking the mouse button more than once makes the spikes “heavier” or more distinct. Of course, by adjusting the opacity control for the brush to less than 100% allows fine control for very delicate, subtle spikes.

The colour of the diffraction spikes can be changed to suit the star in question by the use of the eyedropper tool, to pick the foreground colour from the star.

In general, you will get best results using smaller and fainter spikes on smaller, fainter stars. Figure 7 shows some diffraction spikes of different size and opacity on a plain black background.

Figure 8 shows an image of the Jewel Box (NGC 4755) with some diffraction spikes being added, while Figures 9 and 10 show the before and after images of the Jewel Box.

Experiment, and see what works for you. Adding diffraction spikes to an image, is as much art as creating an appealing image in the first place. Skill and practice are required to get it right.

Best of luck. May you create stunning images.

Figure7.jpgFigure8.jpg

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Figure 7

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Figure 8
Figure9-JewelBoxBefore.jpgFigure10-JewelBoxAfter.jpg

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Figure 9 - Jewelbox before

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Figure 10 - Jewelbox after
Article by Al Sheehan (sheeny). Discuss this article on the IceInSpace Forum.
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