S3TC - Revision history

Andux: /* Containers */ DirectShow Surface -> DirectDraw Surface

2007-07-04T11:37:36Z

Containers: DirectShow Surface -> DirectDraw Surface

← Older revision		Revision as of 04:37, 4 July 2007
Line 74:		Line 74:
	S3TC compressed textures can be found in the following containers:		S3TC compressed textures can be found in the following containers:

	* [[~~DSS DirectShow~~ Surface]] files		* [[DirectDraw Surface]] (DDS) files
	* [[TXD]] Renderware TeXture Dictionaries		* [[TXD]] Renderware TeXture Dictionaries

Ivo: add list of variations and derivatives

2007-04-30T18:02:53Z

add list of variations and derivatives

← Older revision		Revision as of 11:02, 30 April 2007
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	* [[DSS DirectShow Surface]] files		* [[DSS DirectShow Surface]] files
	* [[TXD]] Renderware TeXture Dictionaries		* [[TXD]] Renderware TeXture Dictionaries

			==Variations and derivatives==

			* [[FXT1]]
			* [[3Dc]]

	[[Category: Image Formats]]		[[Category: Image Formats]]

Ivo: description of DXT4/5

2007-04-30T17:52:39Z

description of DXT4/5

@@ Line 33: / Line 33: @@
   uint32_t pixels;
-''alpha'' contains the alpha channel, 4 bits for each pixel. The colors are encoded similar to DXT1, with the exception that the components of ''color2'' and ''color3'' are always calculated by:
+''alpha'' contains the alpha channel, 4 bits for each pixel. The colors and pixels are encoded similar to DXT1, with the exception that the components of ''color2'' and ''color3'' are always calculated by:
   c2 = (2 * c0 + c1) / 3
@@ Line 41: / Line 41: @@
 ==DXT4/5==
 ==Containers==

Ivo: clearer distinction between colors and components; description of dxt2/3

2007-04-30T17:16:21Z

clearer distinction between colors and components; description of dxt2/3

← Older revision		Revision as of 10:16, 30 April 2007
Line 9:		Line 9:
	16 input pixels are encoded as follows:		16 input pixels are encoded as follows:

	uint16_t c0;		uint16_t color0;
	uint16_t c1;		uint16_t color1;
	uint32_t pixels;		uint32_t pixels;

	''c0'' and ''c1'' are RGB565 color values. ''pixels'' are 16 2-bit pixels, referring to ''c0..c3''. Each component of ''c2'' and ''c3'' is calculated by:		''color0'' and ''color1'' are RGB565 color values. ''pixels'' are 16 2-bit pixels, referring to ''color0..3''. Each component of ''color2'' and ''color3'' is calculated by:

	if (c0 > c1)		if (color0 > color1)
	c2 = (2 * c0 + c1) / 3		c2 = (2 * c0 + c1) / 3
	c3 = (2 * c1 + c0) / 3		c3 = (2 * c1 + c0) / 3
Line 22:		Line 22:
	c3 = 0		c3 = 0

	The pixels are stored in raster scan order and start at the least significant two bits of ''pixels''.		The pixels are stored in raster scan order and start at the least significant two bits of ''pixels''. The alpha channel of each pixel is considered fully opaque, except when color0 <= color1. In that case, the alpha channel of color3 is considered fully transparent.

	==DXT2/3==		==DXT2/3==

			16 input pixels are encoded as follows:

			uint64_t alpha;
			uint16_t color0;
			uint16_t color1;
			uint32_t pixels;

			''alpha'' contains the alpha channel, 4 bits for each pixel. The colors are encoded similar to DXT1, with the exception that the components of ''color2'' and ''color3'' are always calculated by:

			c2 = (2 * c0 + c1) / 3
			c3 = (2 * c1 + c0) / 3

			DXT2 considers the pixel values premultiplied by alpha. DXT3 does not.

	==DXT4/5==		==DXT4/5==

Ivo: first draft, explain dxt1 format

2007-04-30T16:53:33Z

first draft, explain dxt1 format

New page

S3 Texture Compression (S3TC) is a family of image compression algorithms developed by S3 for their Savage 3D line of graphics cards. It is also known as DXTn or DXTC.

==Introduction==

S3TC is a lossy compression algorithm that transforms blocks of 4x4 RGBA32 pixels to either 64 or 128 bits. The different compression schemes are often denoted by their Microsoft assigned FourCC.

==DXT1==

16 input pixels are encoded as follows:

uint16_t c0;
uint16_t c1;
uint32_t pixels;

''c0'' and ''c1'' are RGB565 color values. ''pixels'' are 16 2-bit pixels, referring to ''c0..c3''. Each component of ''c2'' and ''c3'' is calculated by:

if (c0 > c1)
c2 = (2 * c0 + c1) / 3
c3 = (2 * c1 + c0) / 3
else
c2 = (c0 + c1) / 2
c3 = 0

The pixels are stored in raster scan order and start at the least significant two bits of ''pixels''.

==DXT2/3==

==DXT4/5==

==Containers==

S3TC compressed textures can be found in the following containers:

* [[DSS DirectShow Surface]] files
* [[TXD]] Renderware TeXture Dictionaries

[[Category: Image Formats]]