High Dynamic Range (Concept)

High Dynamic Range

CONCEPT

A rendering technology using lighting with a larger dynamic range to create more realistic images.

Overview

The color gamut of a CRT monitor (triangular area) as compared to the visible range of the human eye.

Monitor output is, in reality, a highly restricted color space. The color gamut (range of colors shown) is often comparatively small to the entire visual spectrum. In order to emulate the entire range of colors in an image, from blinding whites to pupil adjustment in the dark, some games use larger rendering color spaces than are available with the common modern 24-bit (sometimes referred to as 32-bit for a number of reasons), or 16.7 million colors, color space available on monitors. For example, a game may choose to render an image with a 64-bit range of colors, affording 18.4×10^18 colors.

The game then renders the scene in the standard color mode, adjusting for scene brightness: in a darker scene, it will simulate the eye's greater sensitivity to light due to pupil dilation by displaying darker colors in the normal color space, having only very dark areas fade to completely black, and more bright areas, such as sunlight outside windows, rendered as pure white. In bright outdoor scenes, the opposite is true: the eye is less sensitive to light and therefore only the very brightest areas, such as the sun, will be rendered in pure white, while many more dark areas will be rendered in pure black. Extreme brightness, areas that are excessively bright compared to the current light level, are often supplemented by bloom, an effect where a glow is placed around the excessively bright areas. Adjustment between light levels is typically not instantaneous, mimicking the time it takes for the eye to adjust.

Such rendering is typically done using reprogrammable shaders, such as Shader Model 3.0 in the DirectX API.

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