Step 1- Choose a picture
I used this nice picture that I found on stock exchange (www.sxc.hu3). You can of course use any picture you want. Resize the picture; you can do it at the very end if you want. It helps with the animation.
Step 2- Make it look more suitable.
Now to make a picture have an interesting, dark effect, I like to achieve that by loading the luminosity of the image as a selection and an alpha channel. To do that go to your channels palette. Next ctrl, or command click on the rgb thumbnail to load the luminosity. With that selected, create a new alpha channel.
Now, with that still selected fill it with white,
Then go to Select>Inverse and fill it now with black.
First deselect, next we invert it, Image>Adjustments>Invert, or simply press ctrl or command "I".
Now, switch back to your rgb layers, create a new layer, go to Select>Load Selection make sure it is set to Alpha 1, click ok.
You should now have a selection, with the new layer selected, fill it with black. Ok, play with the opacity to your liking, merge the two layers.
Step 3- Create rain
First create a new layer, fill it with a 50% gray or whatever color you want. Now add 400% noise, check Gaussian, and monochromatic. Now rotate the layer 90 degrees. Then go to Filter>Blur>Blur. After that go to Filter>Stylize>Wind. Choose Blast. Run the filter one more time if you like. Rotate the layer back to the original place. To get the white rain drops, simply invert the layer ctrl I
Alright, to make it look like a never-ending pattern, go to Filter>Other>Offset. Depending on your image the settings may vary. Get rid of the line with the clone stamp, or even the patch tool. Now define the layer as a pattern. We are now done creating the rain.
Step 4 - Animation
Ok, now define the rain as a pattern so go to Edit>Define Pattern. Now you don't need that layer anymore since we saved it as a pattern, delete it or hide it if you want.
Create a new layer, fill it with any color you want, double click on the layer to open the layer styles, choose pattern overlay, the rain you created should be the last on the list. I used soft light for the blend mode, and changed the opacity to 60%. Then go back to the blending options change the fill opacity to 0%.
Alright, time for the actual animation. Go to Window>Animation to open up the timeline.
Click the little clock right next the rain layer name. For me it is called layer 3. That will insert a keyframe, open up the rain layer style box.
Now, hold down shift and drag down a couple of times to simulate the rain fall. Now move the slider to your desired stop time. For me I set it to 3 seconds. With the slider at the end of your animation do the EXACT same thing you did to the first key frame. Doing so will insert a key frame automatically so don't worry about that.
Almost done, move your slider left to right and you should see the animation. It will be choppy because the frames are not rendered. To render the frames just hit the space bar. It may take a while, but you should get a smooth animation simulating rain fall, I recommend making the image smaller.
Conclusion
Ok that pretty much covers it. Pretty quick, and easy. If you want to change the direction of the rain, just convert the layer to a smart object and rotate it. You can even add a fade in, but I will show you how to do that in another tutorial:). Play around with it, have fun.
