Compositing Visible Lights

Hello, I have a question regarding compositing visible lights (I.E, "God Rays).

The question is: how? I’ve struggled a bit to find basic info on how to composite lights specifically; I have my lights in their own layer, nothing else. On this layer, I can render the lights and get a nice image, but I can’t do it with a transparent background, as apparently the “environment” box needs to be checked in order to see the lights.

I could be overthinking this, but where do I mix in the lights? Right now I’m using “Add” to blend them in on the last layer. If I do this, I get the lights, but they’re flat. Is there a standard practice to mixing in lights?

In the render, the lights filter through pipes I have running through the ceiling (the God Rays). How can I recreate this in the compositor?




Thanks for any and all help; let me know if any additional info is needed.

And here’s a pic of the preview render, just to get an idea of what I’m going for (lights streaming through the top ceiling pipes).


Elements that generate additional light are usually comped with add mode. They probably look flat because you render them separate from other scene geometry and they are not hidden by geo that is in front of them. Use other layers as mask in render layer setup to get proper occlusion.

If the added element is a combination of additional light and semi-solid stuff, things get a bit more tricky. Imagine light smoke that is not 100% transparent (actually the case with light rays also) which both “glows” and also covers what is behind it. In this case you can layer them on top of each other with over and add modes to get both emission and occlusion from the smoke/dust etc. Play with mix factors to get proper effect in this case and balance occlusion and emissive look.

I would look toward rendering the beams, then compositing them in to the picture. Don’t attempt to make them actual light sources. You could even take a series of brightly-colored tubes in a layer, yank down the alpha, saturation and contrast, and superimpose them on the scene, simple-masked by the globe.

The “tubes” would be toned-down so that they themselves appeared ghostly, not solid. (Maybe a wee bit of blur would be nice.) Then, you’d use them as a mask against the back image to reduce the saturation of areas “obscured” by the beams, to mimic the visual effect of peering through a beam of light. (Similar in concept to looking through reflective glass e.g. from the outside when it’s night.)

As an old photographer-mentor told me: “Look At The Light!” Never mind what the subject of the picture is, nor what is supposed to be happening there. (Never mind “real life.”) “Look at the light, and to what is objectively happening to it.”

Fantastic answers from both of you, Kesonmis and Sundials.

I’ve managed to successfully composite my lights using the layer masking method; pretty mindblowing the amount of things that can be done with those 20 little checkboxes.

Sundial, I appreciate the method you mentioned. I actually thought about doing something like that, but figured it was too “hacky.” Your validation was needed though; I’m going to implement it and then compare and contrast the results.

Thanks folks.

The industry term for it is “cheating the shot,” and in this context, “cheating is good.” :yes:

CG has so many options and alternative ways of doing things that you can easily be tempted to spend hours doing – and then, re-doing and re-re-re-re-doing – something that is, “arguably, ‘technically perfect.’”

“Perfect, but unnecessary.”

Star Wars Episode One shipped to theaters with a “pod-racer crowd in the grandstands” that actually consisted of variously-colored Q-Tips® cotton swabs. (The shot was replaced in the DVD.) You had previously seen a shot of a real crowd: so, this time, you “saw” them again.

(The trick was revealed in the “Making Of” movie … and, they replaced that bit, too!)

Always try to figure out what will be good enough, especially when it gives you the opportunity to polish-to the final outcome “inexpensively, in-post.” You do not have to try to mimic actual physical reality, even though you usually can. The viewer already knows, from a lifetime of experience, what “physical reality” looks like, and s/he will tend to see that, given only “a suggestion of it.” You can fairly get away with murder, so long as you observe Zach’s demand in the musical “A Chorus Line”: “Don’t draw my eye!”