Originally planned as a section of the Highway 17 chapter of Half-Life 2, Lost Coast is a playable technology showcase that introduces High Dynamic Range lighting to the Source engine. Upon its release, Half-Life 2: Lost Coast will be available free of charge to all owners of Half-Life 2.

Requirements

The Technology

What is HDR?

HDR stands for High Dynamic Range, and is also sometimes referred to as High Dynamic Range Imagery (HDRI) or High Dynamic Range Rendering (HDRR). The Dynamic Range is the ratio of the largest value of a signal to the lowest measurable value. Current 16-bit integer-based formats use colour component values from 0 ("black") to 1 ("white"), but don't allow for what is known as "over-range" values, for example, a whiter-than-white highlight glinting off a piece of metal.

HDR facilitates the use of colour values way outside the normal range in an effort to produce a more realistic rendering of a typical 3D scene. If you have ever driven through a dark tunnel in your car, and then emerged out the other side into blazing sunshine, temporarily blinded by the difference in light levels - that oversaturation is one example of what is possible with HDR

Here is a quick example of HDRI, courtesy of the OpenEXR website - OpenEXR is one standard of HDR developed by Industrial Light & Magic, the world famous California-based studio responsible for almost every eye-popping CG and special effects sequence since Star Wars in 1977.

The original image is on the left: the tree in the foreground is very dark because the overall exposure was influenced by the very bright light in the distance. The middle image is 3 stops brighter, and the right image is 7 stops brighter: the tree detail is now easily visible, and the field in the background is overly bright.

For the average enthusiast, there are only three things to remember about HDR:
 

1. Bright things can be really bright
2. Dark things can be really dark
3. And the details can be seen in both