Version: 2022.3
Language : English
Ambient occlusion
Lightmapping and shaders

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
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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(52.2) 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(22.2) 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 program that runs on the GPU. More info
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(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

You can use HDR lightmaps on Windows, Mac, Linux, iOS, tvOS, and Android. To control the encoding/compression of the lightmaps for these platforms, go to Edit > Project Settings > Player > Other Settings > Lightmap Encoding.

Choosing High Quality will enable HDRhigh dynamic range
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lightmap support, whereas Normal Quality will switch to using RGBM encoding. Low Quality will switch to dLDR encoding on mobile platforms, on other platforms it’s equivalent to Normal Quality.

When lightmap CompressionA method of storing data that reduces the amount of storage space it requires. See Texture Compression, Animation Compression, Audio Compression, Build Compression.
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is enabled in the Lighting Window, the lightmaps will be compressed using the BC6H compression format on desktop and console platforms. For mobile platforms, Unity selects the HDR format according to the table below.

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 real-time rendering by 3D graphics hardware, such as a graphics card or mobile device. More info
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    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 specialized formats which are optimized for fast Texture sampling. More info
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formats per target platform:

Target platform Encoding Compression - size (bits per pixel)
Standalone(PC, Mac, Linux) RGBM / HDR DXT5 / BC6H - 8 bpp
WebGLA JavaScript API that renders 2D and 3D graphics in a web browser. The Unity WebGL build option allows Unity to publish content as JavaScript programs which use HTML5 technologies and the WebGL rendering API to run Unity content in a web browser. More info
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1.0 / 2.0
RGBM DXT5 - 8 bpp
iOS ASTC (1) dLDR / RGBM / HDR ASTC - 3.56 bpp / ASTC - 3.56 bpp / RGB9E5 - 32 bpp
iOS PVRTC dLDR / RGBM / HDR PVRTC RGB - 4 bpp / ETC2 RGBA - 8 bpp / RGB9E5 - 32 bpp
tvOS dLDR / RGBM / HDR ASTC - 3.56 bpp / ASTC - 3.56 bpp / RGB9E5 - 32 bpp
Android ASTC (2) dLDR / RGBM / HDR ASTC - 3.56 bpp / ASTC - 3.56 bpp / ASTC HDR - 3.56 bpp
Android ETC2 dLDR / RGBM / HDR ETC2 RGB - 4 bpp / ETC2 RGBA - 8 bpp / ASTC HDR - 3.56 bpp
Android ETC dLDR / RGBM / HDR ETC1 RGB - 4 bpp / ETC2 RGBA - 8 bpp / ASTC HDR - 3.56 bpp

[1] The texture compression format used for lightmaps on iOS depends on the Texture compression format setting in the Player Settings.

[2] The texture compression format used for lightmaps on Android depends on Player Settings and Build Settings. See Texture compression settings for more details on how these settings interact.

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 Lightmapping and shaders.

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 EXT_texture_shared_exponent.

See also:

  • 2019–04–26 Page amended

  • Baked lightmaps added in Unity 2017.2 NewIn20172

  • HDR lightmap support added in Unity 2017.3 NewIn20173

  • Lightmap encoding settings for mobile platform added in Unity 2019.1 NewIn20191

  • Update lightmap texture compression formats for Android and iOS

Ambient occlusion
Lightmapping and shaders