Translights

You've seen those translucent photographs lit from behind by fluorescent lights before, right? Well, those are Translights. In live-action filmmaking, they often are back-lit photographs or paintings on glass of exteriors. Often slightly-out-of-focus, they sit behind open doors and windows that not only give the camera an image to look at, the light cast through them lands on the actors and set in ways that gives the impression that they're actually on-location.

Translight.lws, is essentially the same thing as using a Translight background on a practical set. We're using a Spinning-Light-Ball with 80, shadow-casting Spotlights, all pointed inward, through a dome that's surface is set to color whatever Lights are Ray-Traced through it.

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While there are minor differences, the result has the same richness and softness as the full-on HDRI/Radiosity render, and at a fraction of the time!

(HDRI/Radiosity: 885.1 seconds, Translight: 128.9 seconds, both at 640x480, Enhanced High Antialiasing.)

Just as with the HDRI/Radiosity render, when you bring the Objects in the Scene closer to specific imagery on the Translight Dome, they take on the colors from that area of the image! And the Translight method uses "real" lights that properly affect the Specularity of your surfaces!

In addition to the Translight Surface being 100% luminous with the same Texture Map applied to it as the HDRI dome, It also has a little trick applied to it to make it visible in the GL preview window, yet 100% transparent during render.

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The base Transparency for the Translight surface is set to 0, so the GL previews will interpret it as opaque... but in its Texture settings, it has the Value, Procedural Texture applied with a Texture Value of 100%, which overrides the base setting during render with a constant value of 100%.

The Translight Surface also has its Alpha Channel set to Constant Value: 0, like with the HDRI dome to give us a clean Alpha for compositing...

But the magic setting that makes the surface act like stained-glass, coloring the Ray-Traced light rays as they pass through it, is to set its Color Filter to 100%.

The Translight dome Object also needs to be set to Unseen by Camera, (and if you don't want it reflecting in the surface of the objects, Unseen by Rays). To help speed renders, it also needs to have Self Shadow and Receive Shadow deactivated.

All of this lets the rays cast by the Lights become colored by the parts of the image through which they pass, even becoming amplified when they pass through a part of the image that has its RGB values higher than 100%.

And the smaller the degree of spin on the oscillators, the sharper the shadows, and the projected image through the "stained glass" of the image... so if you need to tighten-up the GOBO-like shadowing on your object, you can! (Increasing the degree of spin on the oscillators past a certain point makes the cast coloring look muddied.)