A lightmap is a data structure used in lightmapping, a form of surface caching in which the brightness of surfaces in a virtual scene is pre-calculated and stored in

texture maps Texture mapping is a method for mapping a texture on a computer-generated graphic. Texture here can be high frequency detail, surface texture, or color. History The original technique was pioneered by Edwin Catmull in 1974. Texture mapping ...

for later use. Lightmaps are most commonly applied to static objects in applications that use

real-time Real-time or real time describes various operations in computing or other processes that must guarantee response times within a specified time (deadline), usually a relatively short time. A real-time process is generally one that happens in defined ...

3D computer graphics 3D computer graphics, or “3D graphics,” sometimes called CGI, 3D-CGI or three-dimensional computer graphics are graphics that use a three-dimensional representation of geometric data (often Cartesian) that is stored in the computer for t ...

, such as

video game Video games, also known as computer games, are electronic games that involves interaction with a user interface or input device such as a joystick, controller, keyboard, or motion sensing device to generate visual feedback. This fee ...

s, in order to provide lighting effects such as

global illumination Global illumination (GI), or indirect illumination, is a group of algorithms used in 3D computer graphics that are meant to add more realistic lighting to 3D scenes. Such algorithms take into account not only the light that comes directly fro ...

at a relatively low computational cost.

History

John Carmack's Quake was the first computer game to use lightmaps to augment rendering. Before lightmaps were invented, realtime applications relied purely on

Gouraud shading Gouraud shading, named after Henri Gouraud, is an interpolation method used in computer graphics to produce continuous shading of surfaces represented by polygon meshes. In practice, Gouraud shading is most often used to achieve continuous li ...

to interpolate vertex lighting for surfaces. This only allowed low frequency lighting information, and could create clipping artifacts close to the camera without perspective-correct interpolation. Discontinuity meshing was sometimes used especially with radiosity solutions to adaptively improve the resolution of vertex lighting information, however the additional cost in primitive setup for realtime rasterization was generally prohibitive. Quake's software rasterizer used surface caching to apply lighting calculations in texture space once when polygons initially appear within the viewing frustum (effectively creating temporary 'lit' versions of the currently visible textures as the viewer negotiated the scene). As consumer 3d graphics hardware capable of

multitexturing Texture mapping is a method for mapping a texture on a computer-generated graphic. Texture here can be high frequency detail, surface texture, or color. History The original technique was pioneered by Edwin Catmull in 1974. Texture mapping ...

, light-mapping became more popular, and engines began to combine light-maps in real time as a secondary multiply-blend texture layer.

Limitations

Lightmaps are composed of

lumel This is a glossary of terms relating to computer graphics. For more general computer hardware terms, see glossary of computer hardware terms This glossary of computer hardware terms is a list of definitions of terms and concepts related to com ...

s (lumination elements), analogous to texels in

texture mapping Texture mapping is a method for mapping a texture on a computer-generated graphic. Texture here can be high frequency detail, surface texture, or color. History The original technique was pioneered by Edwin Catmull in 1974. Texture mappi ...

. Smaller lumels yield a higher

resolution Resolution(s) may refer to: Common meanings * Resolution (debate), the statement which is debated in policy debate * Resolution (law), a written motion adopted by a deliberative body * New Year's resolution, a commitment that an individual mak ...

lightmap, providing finer lighting detail at the price of reduced performance and increased memory usage. For example, a lightmap scale of 4 lumels per world unit would give a lower quality than a scale of 16 lumels per world unit. Thus, in using the technique,

level design In video games, a level (also referred to as a map, stage, or round in some older games) is any space available to the player during the course of completion of an objective. Video game levels generally have progressively-increasing difficulty t ...

ers and 3d artists often have to make a compromise between performance and quality; if high resolution lightmaps are used too frequently then the application may consume excessive system resources, negatively affecting performance. Lightmap resolution and scaling may also be limited by the amount of disk storage space, bandwidth/download time, or texture memory available to the application. Some implementations attempt to pack multiple lightmaps together in a process known as ''atlasing'' to help circumvent these limitations. Lightmap resolution and scale are two different things. The resolution is the area, in pixels, available for storing one or more surface's lightmaps. The number of individual surfaces that can fit on a lightmap is determined by the scale. Lower scale values mean higher quality and more space taken on a lightmap. Higher scale values mean lower quality and less space taken. A surface can have a lightmap that has the same area, so a 1:1 ratio, or smaller, so the lightmap is stretched to fit. Lightmaps in games are usually colored texture maps, or per vertex colors. They are usually flat, without information about the light's direction, whilst some game engines use multiple lightmaps to provide approximate directional information to combine with normal-maps. Lightmaps may also store separate precalculated components of lighting information for semi-dynamic lighting with shaders, such as ambient-occlusion & sunlight shadowing.

Creation

When creating lightmaps, any lighting model may be used, because the lighting is entirely precomputed and real-time performance is not always a necessity. A variety of techniques including

ambient occlusion In 3D computer graphics, modeling, and animation, ambient occlusion is a shading and rendering technique used to calculate how exposed each point in a scene is to ambient lighting. For example, the interior of a tube is typically more occluded ...

, direct lighting with sampled shadow edges, and full radiosity bounce light solutions are typically used. Modern 3D packages include specific plugins for applying light-map UV-coordinates, atlas-ing multiple surfaces into single texture sheets, and rendering the maps themselves. Alternatively game engine pipelines may include custom lightmap creation tools. An additional consideration is the use of compressed DXT textures which are subject to blocking artifacts – individual surfaces must not collide on 4x4 texel chunks for best results. In all cases,

soft shadows The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object. Assuming no diffraction, for a collimated beam (such as a point source) of light, only the umbra is cast. Th ...

for static geometry are possible if simple occlusion tests (such as basic ray-tracing) are used to determine which lumels are visible to the light. However, the actual softness of the shadows is determined by how the engine interpolates the lumel data across a surface, and can result in a

pixelated Pixelization (British English, pixelisation) or mosaic processing is any technique used in editing images or video, whereby an image is blurred by displaying part or all of it at a markedly lower resolution. It is primarily used for censorshi ...

look if the lumels are too large. See

texture filtering In computer graphics, texture filtering or texture smoothing is the method used to determine the texture color for a texture mapped pixel, using the colors of nearby texels (pixels of the texture). There are two main categories of texture filtering ...

. Lightmaps can also be calculated in real-timeNovember 16, 2003
Dynamic Lightmaps in OpenGL
Joshbeam.com Retrieved Jul. 07, 2014. for good quality colored lighting effects that are not prone to the defects of Gouraud shading, although shadow creation must still be done using another method such as stencil shadow volumes or

shadow mapping Shadow mapping or shadowing projection is a process by which shadows are added to 3D computer graphics. This concept was introduced by Lance Williams in 1978, in a paper entitled "Casting curved shadows on curved surfaces." Since then, it has b ...

, as real-time ray-tracing is still too slow to perform on modern hardware in most 3D engines.

Photon mapping In computer graphics, photon mapping is a two-pass global illumination rendering algorithm developed by Henrik Wann Jensen between 1995 and 2001Jensen, H. (1996). ''Global Illumination using Photon Maps''. nlineAvailable at: http://graphics.stanf ...

can be used to calculate global illumination for light maps.

Alternatives

Vertex lighting

In vertex lighting, lighting information is computed per vertex and stored in vertex color attributes. The two techniques may be combined, e.g. vertex color values stored for high detail meshes, whilst light maps are only used for coarser geometry.

Discontinuity mapping

In discontinuity mapping, the scene may be further subdivided and clipped along major changes in light and dark to better define shadows.

References

Video game design Geometric data structures