Cheap Volumetric Lighting
Cheap volumetric lights? No, contrary to what Google might have you believe, this is not lead on affordable light bulbs, but rather a simple tutorial on creating volumetric lights in Photoshop. While this is really an easy technique, it’s extremely powerful for adding depth and realism to a scene. Of course you can setup volumetric lights in your 3D application, but more often than not, it you end up giving up something in the lights or the rest of scene to get them right, not to mention that they can really add to your render times. This way you can build your scene out as you want and control the lights in Photoshop to get them just right.
For this tutorial I’ll be using Photoshop CS3, but most any version of Photoshop or any image editor with layer support of some sort will work, though you may need to adjust as needed. Since I’m a longtime Mac user, I state keyboard shortcuts and commands specific to Macs, but for PC users, just look for the (brackets) that follow each command for the PC equivalent. Paintshop Pro, Gimp, Pixelmator and other users will have to translate commands and functions for themselves 
To start, you’ll need to open up an image that you want to add volumetric lights to. It doesn’t matter what application you made your image in as this tutorial is all about Photoshop. I’m going to use my Dogg Patrol piece as it was an image where I used this very technique to achieve the desired look for the headlights.While I think I actually did the headlights early on, I’ll be starting with the otherwise completed image and adding them in, though you can of course add your lighting at any point in your post-working.
With your image open, the first step is to create your light’s shape. For the most part, headlights and other low-power light beams are going to be triangle shaped, so draw out a rough, elongated triangle somewhere near the center of your image using the lasso tool. You can draw the light shape in place if you would like, but in the next couple steps, you’ll see why I like to leave a bit of a buffer.
Create a new layer, hit D to reset your foreground and background colors and then hit Cmd+Delete (Ctrl+Backspace) to fill the selected area white. Make sure that you are on working on the newly created layer and don’t fill over your base image.
Deselect by hitting Cmd+D (Ctrl+D). Now it’s time to soften up the light shape a bit by using a Gaussian Blur. Gaussian refers to the bell-shaped curve that is generated when Photoshop applies a weighted average to the pixels while adding low-frequency detail and a nice, hazy effect - perfect for faking volumetric lighting. With the newly filled shape’s layer selected, go to Filter>Blur>Gaussian Blur. In the dialog that comes up, set the radius to 10 pixels and choose ok. As you can see, the blur effect is applied evenly around the pixels of the shape - this is why I always have a buffer in place as anything on or off the edge doesn’t receive the effect.
On a side note, the radius of a Gaussian Blur is largely dependent on the size of the image that you are working with, so you may need to adjust to your liking. For this tutorial, I’ve reduced my base render’s size about 60% to 1600 x 1200, so a 10 pixel radius was just about right, though at it’s original size it might require a much larger radius to achieve the same effect.
Now it’s time to start to make our light look a little more like a light. With the light layer selected, go to the fill (or opacity) slider in the layers pallette and adjust the transparency to about 40%. Like most of these settings, it’s up to you feel looks best, so certainly play around a bit and get it to your liking. Transparency is what is setting the ‘thickness’ of the atmosphere that the light is cutting through, so just make sure it looks right in your environment. Now that it’s starting to look the part, you may want rename your layer L Headlight.
Since most lights are going to be stronger at the source and fade out as they project outward, we need to add some fade to the light. Start by setting your blend mode to Screen in your layer palette. To put it simply, Screen allows only the white pixels on the layer to be seen which is important in what we’re about to do. Lock the transparency of the L Headlight layer and hit G to select the Gradient Tool. If your settings are defaulted to the Paint Bucket Tool, then manually select the Gradient Tool. Make sure your foreground color is set to black and click and drag the gradient tool starting at the wide end of the beam and let go just short of the narrow end.
Not to rip off Emeril, but BAM! Now we’ve got a light beam.
Since we’re looking good and still sitting in the middle of the canvas, it’s about time that we slide the beam into place. Hit V to select the Move Tool and then drag the L Headlight layer to the left, positioning it over the left headlight of the base render. Position the light so that there is a little extra glow around the source and if your original shape wasn’t quite the right size, you can tweak it using Cmd+T (Ctrl+T) and then right-click> Distort. You can now adjust as necessary. If you just need some fine tuning, you can use an appropriately sized soft brush and paint on some black to knock out the white pixels.
Now that we’ve got one headlight, we need to duplicate it over and make the second one. Using the Move Tool, Opt-Drag to the left and the L Headlight layer is duplicated. Since we can’t see the right headlight, approximate it’s position. Obviously we need to remove the excess light beam that’s in front of the vehicle body. Since this is a fairly blocky shape, you can just use the Lasso Tool, Opt-Clicking from point to point. You can also use the pen tool if you are so inclined, though I tend to use the pen on the more complex shapes. However you get your selection made, delete the area of the light over the body and now you’re looking good.
After seeing the lights together, I want to add a little more light to the L Headlight beam as it looks a little thin. Since we still have transparency locked and the blend mode set to screen, grab your Gradient Tool again, hit X to make white the foreground color. Set the Gradient Tool’s opacity to about 40% and drag from the wide end of the beam to the narrow end. This will thicken up the beam a little bit and give it just a little more realism. If you want to add some additional detail to the beams, select them both and paste a good size image of smoke or dust into the selection, using blend modes to get the dust to add a little noise to the lights.
And that’s it. Short of any additional tweaking that you might want to do, you’ve got a set of volumetric lights that fit the bill and took way less time to make than they would have to render. You can of course do any and or all of these steps differently, but that’s how I do it. For instance, if you wanted to use a big, soft eraser, you could just erase the beam instead of using the black gradient of white on screen mode, though preserving the shape of beam comes in handy when you have to add some light back in towards the end. Anyway, I hope this was informative and at least somewhat helpful for some of you out there and if anyone has questions, feel free to drop me a line.
