The Translight Lighting Method: HDRI-Dome Quality At Blazingly Fast Speeds.
By: Timothy Albee

HDRI and "full-on" Radiosity... what a concept! To light CG elements to go into a live-action (or pre-rendered) shot using only an image generated from photographing the actual environment that holds actual real-world lighting data... what a great idea! Too bad that with all the rays that need to be thrown-around to calculate that "real-world-ish" realism, the renders are sloooooo-ooooow.

This is a technique I developed while working on a short film of mine a few years ago when I had to hit high-levels of visual quality, yet had only two home-computers on which I was rendering. This technique yields all the beauty of a full-on HDRI/Radiosity render, but at a fraction of the time! It is a super-simple concept that blends the elegance of real-world thinking with a great, time-proven CGI trick.

HDR Basics

First, let's explore what's involved in a "Real" HDRI/Radiosity render.

Download and extract the Translight_LWS.zip file (Right Click Save As)

Here, we see a character surrounded by an enclosed hemisphere with a funky, "Tie-Dyed" color texture mapped upon it, (this image can be replaced by any hemispherical HDRI image you photograph yourself or find on the 'net). Press to render the frame, and I'll talk about what's going on while the scene renders.

This is a .JPG, (8-bits per channel in Integer format,) version of the .HDR image (32-bits per channel in Floating-Point format) which is mapped onto the hemisphere.

Where an Integer-based image's values go from "1" to "2" to "3"... all the way to its highest value, (in the case of an 8-bit image, that would be from 0 to 255,) a Floating-Point image's values can be almost infinitely divisible steps between any two values. (In Floating-Point, black is usually thought of as 0, [0%,] and white as 1, [100%,] though a PIXEL's value can just as easily be below 0, or above 1.)

8-bits is the minimum a human eye needs to perceive a continuous tone within that channel.

32, floating-point bits-per-channel, obviously, holds a lot more data per channel, which is vital when pushing a rendered frame's colors around significantly in compositing.

An HDR image that can have color values be "hotter" than "255, 255, 255" white. This means that an HDR photograph of a light with values of "800%, 800%, 800%" would actually "cast" eight times the light of a flat-lit, "100%, 100%, 100%" white sheet of paper in the same photograph!