Adaptive scalable texture compression: Difference between revisions

Revision as of 12:38, 7 August 2012

Revision as of 18:31, 7 November 2012

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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 
Texture Compression Specification|publisher=The Khronos Group Inc.|date=2012-08-06|accessdate=2012-08-06}}</ref>

=== Overview ===

[[File:Original_Image_before_ASTC_compression.jpg|thumb|right|Example image prior to compression]][[File:Detail_of_ASTC_compressed_image.png|thumb|right|Detail from example image, after compression at 4, 3.56 and 2 bits/pixel]]The method of compression is an evolution of [[Color Cell Compression]] with features including numerous closely spaced fractional bit rates, multiple color formats, support for High Dynamic Range (HDR) textures, and real 3D texture support.

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Despite this flexibility, ASTC achieves better peak signal-to-noise ratios than [[PVRTC]], [[S3TC]], and [[Ericsson Texture Compression|ETC2]] when measured at 2 and 3.56 bits per texel. For HDR textures, it produces results comparable to BC6H at 8 bits per texel.

=== Supported Color Formats ===

{| class="wikitable"

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Each of these may be encoded as low or high dynamic range. The encoder selects color formats independently for each block in the image.

=== 2D Block Footprints and Bit Rates ===

ASTC textures are compressed using a fixed block size of 128 bits, but with a variable block footprint ranging from 4x4 texels up to 12x12 texels. The available bit rates thus range from 8 bits per texel down to 0.89 bits per texel, with fine steps in between.

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In the above table, the "Increment" column shows the additional storage required to store a texture using this bit rate, as compared to the next smallest. Block footprints are presented as width x height.

=== 3D Block Footprints and Bit Rates ===

ASTC 3D textures are compressed using a fixed block size of 128 bits, as for 2D but with a variable block footprint ranging from 3x3x3 texels up to 6x6x6 texels. The available bit rates thus range from 4.74 bits per texel down to 0.59 bits per texel, with fine steps in between.