Step 1: Add noise
Rain is basicly small drips of water, so to save time we will use filters to create the drips. Create a new document with greater size than your photo, make it double or something like that.
Fill the background layer with black. Then add a Noise-filter.
Filter > Noise > Add Noise
(Ammount: 20-40%)
(Distribution; Gaussian and Monochromatic)
Step 2: Motion blur
Right now, we have our small drips (basicly small white dots) that are freezed. Usually, rain falls. So I suggest we add a Motion blur-filter to give our drips the speed they deserve.
Filter > Blur > Motion Blur
(Angle: Choose the angle of your rain (-63)
(Distance: Choose the speed of the drips (21))
Step 3: Adjust levels
If you ask me, I would say that the image right now is too noisy and flat for our purpose. Easy to fix, by adjusting the image’s Levels!
Image > Adjustments > Levels
This was the last step for the first part of this tutorial. In the next part I will show you how to apply the rain to your photos.
Applying the rain to a photograph
All right, we have now got our rain and the final step is to apply the rain to a photo. The tecnique is basicly based on blending and the trick is to create an illusion of depth in the rain.
Move your rain-layer and place it on top of a photo. Then change the Blending mode to Screen.
That is all you need to make a scene look rainy. You might want to adjust the opacity or maybe duplicate the rain-layer to increase the ammount of rain.
Here are some result pictures of what you can achive using this technique in Adobe Photoshop.See before/after
