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Up the bits.

Introduction

HDR stands for high-dynamic-range. Most current hardware & software deals only with LDR rendering; using 8 bits to represent 256 levels of brightness (in Red, Green and Blue). With HDR, you go beyond these 256 levels to have more contrast. With LDR the best ratio is 256:1 (if you use a linear brightness system); with HDR 16-bits half float you can go much higher. You have to move away from thinking in 0..1 levels and starting thinking in luminance levels.

For background material, try these:

• Luminance values
• Local luminance and contrast in natural images

Background information on tonemapping

This gets technical. To get from HDR (16 or more bits) to 8-bits (LDR, what most monitors handle), you need tonemapping. Tonemapping is selecting which HDR lighting values you map to the limited range of monitors. A digital camera can capture around 4 stops of dynamic range; an eye can distinguish around 12 stops.

The original tonemapping in Racer was based on the exp() function. This squeezes the top part (whites) so detail is maintained. This is sometimes called the 'shoulder' of the tonemap curve. It seems you als want to have a 'toe' in the curve, to get better blacks. This is what Uncharted 2 used for example. Also, God of War III used a Reinhard method, which normally only does shoulder, but they added some stuff to add a toe (most probably, from what I gathered on the net).

Very interesting reads, if you can follow it, is here:

• John Hable's tonemapping in Cg - explains Reinhard, Filmic (from Uncharted 2).
• Reinhard using luminance - a response to the above article, using luminance to scale RGB equally. However, the comments state that separate RGB tonemapping is precisely what film does, and the saturation/color shifts that come with it are intentional and useful (though I'm not sure why). Kodak wasn't just fooling around when they made their films.
• Why a Filmic Curve Saturates Your Blacks - explains the little toe in the filmic curve (by John Hable)
• SIGGRAPH 2010 course - color enhancement and rendering in film and game production (notice the link between film & games)

In Racer v0.8.22, I got Uncharted2 tone mapping to work finally. Gives a nice touch, a sort of look to things.

(last updated November 13, 2012 )