Lightmaps: Technical information

Unity stores lightmapsA pre-rendered texture that contains the effects of light sources on static objects in the scene. Lightmaps are overlaid on top of scene geometry to create the effect of lighting. More info
See in Glossary with different compressions and encoding schemes, depending on the target platform and the compression setting in the Lighting Window.

Encoding schemes

Unity projects can use two techniques to encode baked light intensity ranges into low dynamic range textures when this is needed:

• RGBM encoding. RGBM encoding stores a color in the RGB channels and a multiplier (M) in the alpha channel. The range of RGBM lightmaps goes from 0 to 34.49(5^2.2) in linear space, and from 0 to 5 in gamma space.

• Double Low Dynamic Range (dLDR) encoding. dLDR encoding is used on mobile platforms by simply mapping a range of [0, 2] to [0, 1]. Baked light intensities that are above a value of 2 will be clamped. The decoding value is computed by multiplying the value from the lightmap texture by 2 when gamma space is used, or 4.59482(2^2.2) when linear space is used. Some platforms store lightmaps as dLDR because their hardware compression produces poor-looking artifacts when using RGBM.

When Linear Color Space is used, the lightmap texture is marked as sRGB and the final value used by the shadersA small script that contains the mathematical calculations and algorithms for calculating the Color of each pixel rendered, based on the lighting input and the Material configuration. More info
See in Glossary (after sampling and decoding) will be in Linear Color Space. When Gamma Color Space is used, the final value will be in Gamma Color Space.

Note: When encoding is used, the values stored in the lightmaps (GPU texture memory) are always in Gamma Color Space.

The Decode Lightmap shader function from the UnityCG.cginc shader include file handles the decoding of lightmap values after the value is read from the lightmap texture in a shader.

HDR lightmap support

HDR lightmaps can be used on PC, Mac & Linux Standalone, Xbox OneMicrosoft’s eighth generation video game console.
See in Glossary, and PlayStation 4. The Other Settings panel in the Player settings has a Lightmap Encoding option for these platforms, which controls the encoding/compression of the lightmaps.

Choosing High Quality will enable HDRhigh dymanic range
See in Glossary lightmap support, whereas Normal Quality will switch to using RGBM encoding.

When lightmap CompressionA method of storing data that reduces the amount of storage space it requires. See Texture Compression, Animation CompressionThe method of compressing animation data to significantly reduce file sizes without causing a noticable reduction in motion quality. Animation compression is a trade off between saving on memory and image quality. More info
See in Glossary, Audio Compression, Build Compression.
See in Glossary is enabled in the Lighting Window, the lightmaps will be compressed using the BC6H compression format.

Advantages of High Quality (BC6H) lightmaps

• HDR lightmaps don’t use any encoding scheme to encode lightmap values, so the supported range is only limited by the 16-bit floating point texture formatA file format for handling textures during realtime rendering by 3D graphics hardware, such as a graphics card or mobile device. More info
  See in Glossary that goes from 0 to 65504.

• BC6H format quality is superior to DXT5 + RGBM format encoding, and it doesn’t produce any of the color banding artifacts that RGBM encoding has.

• Shaders that need to sample HDR lightmaps are a few ALU instructions shorter because there is no need to decode the sampled values.

• BC6H format has the same GPU memory requirements as DXT5.

Here is the list of encoding schemes and their texture compression3D Graphics hardware requires Textures to be compressed in specialised formats which are optimised for fast Texture sampling. More info
See in Glossary formats per target platform:

*If the target is Android then you can override the default texture compression format from the Build Settings to one of the following formats: DXT1, PVRTC, ATCAMD’s texture compression format for handheld devices to save on power, memory and bandwidth
See in Glossary, ETC2, ASTC. The default format is ETC.

Precomputed real-time Global Illumination (GI)

The inputs to the GI system have a different range and encoding to the output. Surface albedo is 8-bit unsigned integer RGB in gamma space and emission is 16-bit floating point RGB in linear space. For advice on providing custom inputs using a meta pass, see documentation on Meta pass.

The irradiance output texture is stored using the RGB9E5 shared exponent floating point format if the graphics hardware supports it, or RGBM with a range of 5 as fallback. The range of RGB9E5 lightmaps is [0, 65408]. For details on the RGB9E5 format, see Khronos.org: EXT_texture_shared_exponent.

See also:

• Texture Importer Override
• Texture Types
• Global Illumination
• Texture Types
• Global Illumination

• 2017–09–18 Page amended with no editorial review

• Baked lightmaps added in Unity 2017.2 NewIn20172

• HDR lightmap support added in Unity 2017.3 NewIn20173