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High dynamic range rendering 60
Tone mapping
Tone mapping, in the context of graphics rendering, is a technique used to map colors from high dynamic range (in
which lighting calculations are performed) to a lower dynamic range that matches the capabilities of the desired
display device. Typically, the mapping is non-linear – it preserves enough range for dark colors and gradually limits
the dynamic range for bright colors. This technique often produces visually appealing images with good overall
detail and contrast. Various tone mapping operators exist, ranging from simple real-time methods used in computer
games to more sophisticated techniques that attempt to imitate the perceptual response of the human visual system.
Applications in computer entertainment
Currently HDRR has been prevalent in games, primarily for PCs, Microsoft's Xbox 360, and Sony's PlayStation 3. It
has also been simulated on the PlayStation 2, GameCube, Xbox and Amiga systems. Sproing Interactive Media has
announced that their new Athena game engine for the Wii will support HDRR, adding Wii to the list of systems that
support it.
In desktop publishing and gaming, color values are often processed several times over. As this includes
multiplication and division (which can accumulate rounding errors), it is useful to have the extended accuracy and
range of 16 bit integer or 16 bit floating point formats. This is useful irrespective of the aforementioned limitations in
some hardware.
Development of HDRR through DirectX
Complex shader effects began their days with the release of Shader Model 1.0 with DirectX 8. Shader Model 1.0
illuminated 3D worlds with what is called standard lighting. Standard lighting, however, had two problems:
1. Lighting precision was confined to 8 bit integers, which limited the contrast ratio to 256:1. Using the HVS color
model, the value (V), or brightness of a color has a range of 0 – 255. This means the brightest white (a value of
255) is only 256 levels brighter than the darkest shade above pure black (i.e.: value of 0).
2. Lighting calculations were integer based, which didn't offer as much accuracy because the real world is not
confined to whole numbers.
Before HDRR was fully developed and implemented, games may have attempted to enhance the contrast of a scene
by exaggerating the final render's contrast (as seen in Need For Speed: Underground 2's "Enhanced contrast" setting)
or using some other color correction method (such as in certain scenes in Metal Gear Solid 3: Snake Eater).
On December 24, 2002, Microsoft released a new version of DirectX. DirectX 9.0 introduced Shader Model 2.0,
which offered one of the necessary components to enable rendering of high dynamic range images: lighting precision
was not limited to just 8-bits. Although 8-bits was the minimum in applications, programmers could choose up to a
maximum of 24 bits for lighting precision. However, all calculations were still integer-based. One of the first
graphics cards to support DirectX 9.0 natively was ATI's Radeon 9700, though the effect wasn't programmed into
games for years afterwards. On August 23, 2003, Microsoft updated DirectX to DirectX 9.0b, which enabled the
Pixel Shader 2.x (Extended) profile for ATI's Radeon X series and NVIDIA's GeForce FX series of graphics
processing units.
On August 9, 2004, Microsoft updated DirectX once more to DirectX 9.0c. This also exposed the Shader Model 3.0
profile for high level shader language (HLSL). Shader Model 3.0's lighting precision has a minimum of 32 bits as
opposed to 2.0's 8-bit minimum. Also all lighting-precision calculations are now floating-point based. NVIDIA states
that contrast ratios using Shader Model 3.0 can be as high as 65535:1 using 32-bit lighting precision. At first, HDRR
was only possible on video cards capable of Shader-Model-3.0 effects, but software developers soon added
compatibility for Shader Model 2.0. As a side note, when referred to as Shader Model 3.0 HDR, HDRR is really
done by FP16 blending. FP16 blending is not part of Shader Model 3.0, but is supported mostly by cards also
capable of Shader Model 3.0 (exceptions include the GeForce 6200 series). FP16 blending can be used as a faster