Here’s how to create rain using a few Photoshop filters, as well as how to turn it into a brush that you can keep and use in the future.
Press D to set the foreground and background colors to their default of black and white. Create a new document by going File > New. Set Width to 1200px, Height to 800px, and Resolution to 240ppi, and click OK (Figure 4.33). (It doesn’t matter what color you set as Background Contents so long as you don’t use Transparent.)
Go to Filter > Noise > Add Noise, set Amount to 400%, and choose Gaussian and Monochromatic (Figure 4.34). Click OK. Go to Filter > Blur > Motion Blur, and set Angle to –52 and Distance to 70 pixels (Figure 4.35).
You may notice that the motion blur around the edges of the file don’t look quite right (Figure 4.36). Go to Edit > Free Transform, Shift+Option/Alt-click a corner transform handle, and drag outward until the edges aren’t visible. Press Return/Enter.
Go to Image > Adjustments > Levels, choose the Black Point sampler, and then click within the image. This changes the look of the layer entirely, and you’ll see lines appear that we’ll be able to use as rain (Figure 4.37). Try clicking around different areas of the layer, which will create results with more or less rain. Once you have the look you’re after, click OK.
To turn this rain effect into a brush, go to Image > Adjustments > Invert so that the rain effect is now black against a white background. Photoshop uses the dark and gray areas to form the brush, ignoring the white areas. Go to Edit > Define Brush preset, name the preset rain, and click OK.