High Dynamic Range Rendering
High Dynamic Range Rendering ( HDRR ), in computer graphics image synthesis ( " rendering " ) taking into account the naturally occurring large fluctuations in brightness. In contrast to the conventional 256 brightness levels per color channel colors are represented internally with sufficiently high precision to cover a very large range of brightnesses at HDRR. This permits the display of stark contrasts without excessive loss of detail and the use of effects such as simulating lens dispersion.
A special technique from the HDRR range is the image-based lighting, in which a computer graphics scene enveloped by an HDR image and is illuminated. This gives the impression that artificially modeled objects would be inserted in a natural environment.
HDRR during real-time rendering
When hardware-assisted HDRR - real-time rendering the graphics card processes the color information internally so that a large brightness range is covered and that rounding errors are kept low. These colors must be represented with a higher space. With a too low accuracy the color transitions would be so rude sometimes that this visible artifacts ( color gradations ) would result.
The result of the HDRR process is an HDR image, the dynamic range must be reduced to representation by means of tone mapping. Because it is tried when tone mapping to preserve image details, even scenes with great brightness contrast can be shown to be limited by a low brightness range without very bright or very dark areas and appear as pure black or pure white. An example of a scene in which the benefits of HDRR be clear, is a dark cave that leads into a sunlit exterior. The tone mapping operator adapts to these different brightness levels, so that the absolute brightness values in the scene are optimally transferred to the low dynamic range of the screen.
HDRR as a technology for computer games was about the same time with the Shader Model 3.0 of DirectX available. However, these two technologies have little to do with each other, for example, it is shown that in theory, any DirectX 9 graphics card is able to represent the HDRR Effects: Any DirectX 9 graphics card must be in the pixel shader internally at least 24 bits per color channel support ( " FP24 " ) and textures at 32 bits per color channel ( " FP32 " ) can read, but this would lead to older cards to significant performance degradation. The hardware of current games consoles such as the GPU from ATI developed the Xbox 360 or the PlayStation 3 NVIDIA GPU support HDRR also.
HDRR found inter alia in Unreal Engine 3, the first-person shooter Far Cry from version 1.3 or in some maps in Counter- Strike use. Very clearly HDRR effects in the racing game Project Gotham Racing 3 and in the first-person shooter Halo 3 are used.
Image-based lighting
In image-based lighting (IBL ) is completely known from a HDR environment map, even light probe a scene wrapped. A HDR environment map can be generated by being directly absorbed by special cameras with rotating lens or fisheye lens. Alternatively, an environment reflective ball photographed or more individual photos are stitched. The image is then optionally transformed into a cube or a sphere that encloses the scene.
One of the problems that must be solved in the IBL, is bright regions of the environment map preferable to scan to enable the Monte Carlo ray tracing importance sampling. Ideally, the sampling positions are distributed so that they have a great distance from each other, yet show no ordered pattern ( blue noise ). Very bright, concentrated regions such as the sun not only require special techniques in the recording, but also be removed from the environment map and explicitly modeled, since there would otherwise be a very strong noise ( individual bright pixels ).
An important application is IBL in film effects to represent artificial objects and beings as if they were actually present in the recording.
- Examples of illuminated scenes by IBL