HDR: Difference between revisions

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[[Image:HL2_LostCoast_17.jpg|thumb|right|An example of HDR effect, as seen in [[Lost Coast]]]]
[[Image:HL2_LostCoast_17.jpg|thumb|right|An overexposed image from [[Lost Coast]]]]


'''HDR''' or '''High Dynamic Range''' is used as the name for a feature introduced into the [[Source]] engine with [[Half-Life 2: Lost Coast]] and [[Day of Defeat: Source]].  
'''HDR''' ('''High Dynamic Range''') rendering simulates brightness above that which a computer monitor is actually capable of displaying. This mainly involves "blooming" colours above 100% brightness into neighbouring areas, and adjusting a virtual camera [[W:aperture|aperture]] to compensate for any over-exposure that results.


For the player, Valve's [http://www.steampowered.com/Steam/Marketing/June24.2005/"dynamic tonemapping"] simulates the way that a human eye (or a camera with auto-exposure) gradually adjusts to compensate for changes in illumination levels, such as when entering a dark room from a daylit street or vice versa. As well as exposure-shifting to suit the ''average'' light level of the scene, the HDR feature also depicts '''burn-out''' (flat white with ''bloom'' halo) in over-bright areas, and '''flat shadows''' (black) in over-dark areas of the scene.
Beside the obvious effects of this (see right), HDR gives richer colours and finer gradients: since bright and dark areas are pushed into white and black, correctly-exposed areas are drawn with a far wider range of values.


For example, standing in a street in bright daylight, the window of a house appears black - you cannot see any details of the room behind the window. On entering the house the interior still appears black until your eyes gradually adjust to the lower light level, and then you can see the furniture, etc. Now looking at the small window to the street from inside the house, the illumination outside is far too bright for your eyes tuned to the interior light level, so you just see a slab of blooming bright white light instead of the street or sky beyond.
== In Source ==


The advantage of this 'LDR' view of an 'HDR' scene is that the correctly-exposed parts of the image are rendered in full detail; using all 8 bits per RGBA channel to describe the fine gradations of local colour and tone on the Player's screen.
Source does not have a physically accurate HDR simulation. Its camera has a far wider range than the human eye (let alone real cameras), and it also adjusts to changes in brightness far faster. Both of these are expedient to gameplay of course, especially in multiplayer.
 
In fact Source does not even create 'proper' HDR images: instead [http://www.valvesoftware.com/publications/2006/SIGGRAPH06_Course_HDRInValvesSourceEngine_Slides.pdf it collapses the image down to LDR early]. The average user would be hard pressed to tell the difference however, and the benefits include support for all DX9 GPUs, MSAA compatibility, and excellent performance.


== See also ==
== See also ==
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== External links ==
== External links ==
* [[Wikipedia:High dynamic range rendering]]
* [[Wikipedia:High dynamic range rendering]]
* [[Wikipedia:High dynamic range imaging]]
* [http://www.daionet.gr.jp/~masa/rthdribl/ Real-Time High Dynamic Range Image-Based Lighting] - a demo for DX9-level video cards.
* [http://www.daionet.gr.jp/~masa/rthdribl/ Real-Time High Dynamic Range Image-Based Lighting] - a demo for DX9-level video cards.
* [http://www.steampowered.com/Steam/Marketing/June24.2005/ 6.24.2005 Steam Update News with explanation and video of HDR]
* [http://gl.ict.usc.edu/HDRShop/ HDR Shop]


[[Category:Technical]]
[[Category:Technical]]
[[Category:Glossary]]
[[Category:Glossary]]

Revision as of 12:09, 15 January 2011

An overexposed image from Lost Coast

HDR (High Dynamic Range) rendering simulates brightness above that which a computer monitor is actually capable of displaying. This mainly involves "blooming" colours above 100% brightness into neighbouring areas, and adjusting a virtual camera aperture to compensate for any over-exposure that results.

Beside the obvious effects of this (see right), HDR gives richer colours and finer gradients: since bright and dark areas are pushed into white and black, correctly-exposed areas are drawn with a far wider range of values.

In Source

Source does not have a physically accurate HDR simulation. Its camera has a far wider range than the human eye (let alone real cameras), and it also adjusts to changes in brightness far faster. Both of these are expedient to gameplay of course, especially in multiplayer.

In fact Source does not even create 'proper' HDR images: instead it collapses the image down to LDR early. The average user would be hard pressed to tell the difference however, and the benefits include support for all DX9 GPUs, MSAA compatibility, and excellent performance.

See also

External links

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