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{{Short description|Computer graphics algorithm}}
'''Adaptive scalable texture compression''' ('''ASTC''') is a [[lossy compression|lossy]] block-based [[texture compression]] [[algorithm]] developed by Jørn Nystad et al. of [[ARM Holdings|ARM Ltd.]] and [[Advanced Micro Devices|AMD]].<ref>{{cite web |url=https://www.arm.com/products/multimedia/mali-technologies/adaptive-scalable-texture-compression.php |title=Adaptive Scalable Texture Compression (ASTC) technology developed by ARM
Full details of ASTC were first presented publicly at the High Performance Graphics 2012 conference, in a paper by Olson et al. entitled "Adaptive Scalable Texture Compression".<ref name=astc_paper>{{cite web|url=https://www.cs.cmu.edu/afs/cs/academic/class/15869-f11/www/readings/nystad12_astc.pdf|title=Adaptive Scalable Texture Compression |publisher=HPG 2012 |date= |accessdate=2012-06-27}}</ref>
ASTC was adopted as an official extension for both [[OpenGL]] and [[OpenGL ES]] by the [[Khronos Group]] on 6 August 2012.<ref>{{cite web|url=http://www.khronos.org/news/press/khronos-releases-atsc-next-generation-texture-compression-specification|title=Khronos Releases ATSC Next-Generation
== Hardware support ==
{| class="wikitable"
* ARM [[Mali (GPU)|Mali]] GPUs starting from Mali-T620, Mali-T720 and Mali-T820 have full ASTC support.<ref>{{cite web|url=https://developer.arm.com/-/media/Arm%20Developer%20Community/PDF/Mali%20GPU%20datasheet/Arm%20Mali%20GPU%20Datasheet%202021.pdf?revision=d3378de8-806b-4920-897c-e295509847b3|title=Arm Mali GPU Datasheet|date=2021|accessdate=2021-08-31|publisher=[[Arm Limited]]</ref>▼
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* Nvidia's [[Kepler (microarchitecture)|Kepler]] and [[Maxwell (microarchitecture)|Maxwell]]-based [[Tegra]] SoCs support ASTC.<ref>{{cite web |url=http://on-demand.gputechconf.com/siggraph/2015/presentation/SIG1501-Piers-Daniell.pdf |title=Vulkan API}}</ref>▼
! Vendor/product !! Profile !! Generation
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* [[Apple silicon|Apple]] GPUs from [[Apple A8|A8]] onwards support LDR, and GPUs from [[Apple A13|A13]] onwards support HDR.<ref>{{cite web|url=https://developer.apple.com/metal/Metal-Feature-Set-Tables.pdf|title=Metal Feature Set Tables|accessdate=2021-08-31|date=2020-10-21|publisher=[[Apple Inc]]}}</ref>▼
| AMD [[Radeon]] || || ?
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|style="background:#9F9"| Full || Since [[Apple A13|A13]]<ref name=apple />
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| [[Imagination Technologies|Imagination]] [[PowerVR]] ||style="background:#9F9"| Full || Since Series6XT<ref>{{cite web|url=https://www.imaginationtech.com/news/press-release/imaginations-new-generation-powervr-series6xt-architecture-delivers-up-to-50-higher-performance-and-advanced-power-management/|title=Imagination's new generation PowerVR Series6XT architecture delivers up to 50% higher performance and advanced power management|date=2014-01-06|accessdate=2021-08-21|publisher=[[Imagination Technologies]]}}{{Dead link|date=August 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
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| [[Intel HD and Iris Graphics|Intel GPUs]] ||style="background:#9F9"| Full<ref>{{cite web|url=https://www.phoronix.com/scan.php?page=news_item&px=ASTC-Skylake-Intel-Mesa|website=Phoronix|title=Intel Skylake Adds ASTC Texture Compression, Open-Source Support Coming|date=2015-05-20|accessdate=2021-08-31}}</ref> || From [[Skylake (microarchitecture)|Skylake]]<ref>{{cite web |url=https://software.intel.com/en-us/articles/6th-gen-graphics-api-dev-guide|archiveurl=https://web.archive.org/web/20170720043433/https://software.intel.com/en-us/articles/6th-gen-graphics-api-dev-guide|archivedate=2017-07-20|title=Graphics API Developer's Guide For 6th Generation Intel Core Processors}}</ref> <span style="color:darkred">; Removed in [[Intel Arc|Arc]] / Gen12.5</span><ref>{{cite web|url=https://www.phoronix.com/scan.php?page=news_item&px=Intel-Gen12.5-No-ASTC|title=Intel Removes ASTC Hardware From Gen12.5+ Graphics|author=Michael Larabel|date=2021-10-07|accessdate=2022-07-10|website=[[Phoronix]]}}</ref>
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| [[Qualcomm]] [[Adreno]] ||style="background:#9F9"| Full || LDR since 4xx series,<ref>{{cite web|url=https://developer.qualcomm.com/qfile/28557/80-nu141-1_b_adreno_opengl_es_developer_guide.pdf|date=2015-05-01|accessdate=2021-08-31|title=Qualcomm Adreno OpenGL ES Developer Guide|publisher=[[Qualcomm]]}}</ref> at least 7xx series support GL_KHR_texture_compression_astc_hdr extension on Android 13
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On Linux, all Gallium 3D drivers have a software fallback since 2018, so ASTC can be used on any AMD Radeon GPU.<ref>{{cite web|url=https://lists.freedesktop.org/archives/mesa-dev/2018-July/200867.html |title=[Mesa-dev] [PATCH 0/7] ASTC texture compression for all Gallium drivers |publisher=Lists.freedesktop.org |date= 23 July 2018|accessdate=2022-09-01}}</ref>
== Overview ==
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== Supported color formats ==
ASTC supports anywhere from 1 to 4 channels. In modes with 2–4 channels, one of the channels can be treated as "uncorrelated" and be given a separate gradient for prediction. In any case, the data is decoded as RGBA.<ref>{{cite web |title=Khronos Data Format Specification v1.1 rev 9 |url=https://registry.khronos.org/DataFormat/specs/1.1/dataformat.1.1.html#ASTC |website=registry.khronos.org}}</ref>
{| class="wikitable"
|- style="text-align:center;"
! Channel count
! RGBA interpretation
! Description
|- style="text-align:center;"
| 1 || L || Luminance-only: RGB set to same value in decoded buffer, alpha set to 1
| LA || Luminance with transparency▼
|- style="text-align:center;"
|
|- style="text-align:center;"
|- style="text-align:center;"
| 3 || RGB || Full color, alpha set to 1
|- style="text-align:center;"
|
|- style="text-align:center;"
| 4 || RGBA || Full color with transparency
|- style="text-align:center;"
| 4 || RGB+A || Full color with uncorrelated transparency
|}
Each of these may be encoded as low or high dynamic range. The encoder selects color formats independently for each block in the image.
In practice, ASTC may be used to represent data other than color. For example, the L+A format may be used to represent "X+Y", a [[Normal mapping|normal map]] with uncorrelated components; the "RG+B" format can be used to represent XY+Z.<ref>{{cite web |title=Khronos Releases ASTC Next-Generation Texture Compression Specification |url=https://www.khronos.org/news/press/khronos-releases-atsc-next-generation-texture-compression-specification |website=The Khronos Group |language=en |date=6 August 2012}}</ref> The {{code|astc-encoder}} software supplied by ARM supports "X+Y" generation with the {{code|-normal}} option. The shader is expected to treat the decoded output as a [[swizzled texture]].<ref>{{cite web |title=Effective ASTC Encoding [astc-encoder/Docs/Encoding.md at 2042cfc1a507c0414fb41dce1603ed53c503a0da · ARM-software/astc-encoder] |url=https://github.com/ARM-software/astc-encoder/blob/2042cfc1a507c0414fb41dce1603ed53c503a0da/Docs/Encoding.md |website=GitHub |language=en |quote=The best way to store normal maps using ASTC is similar to the scheme used by BC5; store the X and Y components of a unit-length normal. The Z component of the normal can be reconstructed in shader code based on the knowledge that the vector is unit length. To encode this we need to store only two input components in the compressed data, and therefore use the rrrg coding swizzle to align the data with the ASTC luminance+alpha endpoint.}}</ref>
== 2D block footprints and bit rates ==
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Block footprints are presented as width × height × depth.
== Universal ASTC ==
UASTC (Universal ASTC) is a subset of ASTC specified by Binomial. The format is used in their Basis Universal "[[texture supercompression|supercompressed]]" GPU texture format, which adds extra compression over compressed texture formats such as UASTC and [[ETC1|ETC1S]] and allows for efficient conversion from UASTC/ETC1S to compressed texture formats directly usable by GPUs.<ref>{{cite web |title=UASTC Texture Specification |url=https://github.com/BinomialLLC/basis_universal/wiki/UASTC-Texture-Specification |website=GitHub |language=en}}</ref> UASTC, as part of Basis Universal, is part of the KTX (Khronos Texture) file format.<ref>{{cite web |title=KTX - GPU Texture Container Format |url=https://www.khronos.org/ktx/ |website=The Khronos Group |language=en |date=16 April 2021}}</ref>
== See also ==
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* [https://github.com/ARM-software/astc-encoder ASTC Evaluation Codec from ARM]
* [http://www.khronos.org/registry/gles/extensions/OES/OES_texture_compression_astc.txt Khronos ASTC Full Profile Extension Specification]
{{Compression methods}}
[[Category:Lossy compression algorithms]]
[[Category:Texture compression]]
[[Category:
[[Category:Data compression]]
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