FLEXIBLE TEXTURE COMPRESSION USING BOUNDED INTEGER SEQUENCE ENCODING

彬彬

1 Introduction

Memory bandwidth is a critical resource in modern graphics accelerators,

particularly those intended for use in mobile devices.

Texture fetches often make up a large fraction of total graphics accelerator

bandwidth, so there is great interest in methods of compressing

textures for real-time decode during rendering [Akenine-

M¨oller and Str¨om 2003]. These methods typically partition the image

into fixed-size blocks, and encode each block as a fixed number

of bits. The bits describing each block are further partitioned into

data items specifying per-block control information (e.g., mode selection),

per-block color information (e.g., color space definition),

and per-***l color information (e.g., color indices). In order to allow

efficient random access during decoding, each item is typically

encoded in an integer number of bits. This is inefficient if the number

of distinct values an item can take on is not a power of two,

which places severe constraints on how the data items are defined.

In this paper we describe a texture compression system in which

data items can be represented by fractional numbers of bits, using

a low-level coding scheme called Bounded Integer Sequence Encoding.

This allows bits to be allocated among different types of

information in a very flexible way without sacrificing coding efficiency.

The system uses this flexibility to offer an unusually wide

range of functionalities. It handles images with one to four components

per ***l at bit rates from 8bpp down to less than 1bpp,

with quality comparable to state-of-the-art formats in each case. It

supports both 8-bit per component and HDR ***l formats, and can

encode both 2D and 3D images.

2 Related Work

Our method is similar to [Str¨om and Pettersson 2007; Iourcha et al.

1999] and others in that it partitions the image ***ls into blocks,

and provides color indices that associate ***ls with points along

lines in color space. Like BPTC [OpenGL ARB 2010], our method

assigns ***ls within a block to partitions, and defines a different

color space for each partition. Our method differs from previous

work in that a great deal of information is specified on a per-block

or per-partition basis; this includes the number of color channels

per ***l and the ***l dynamic range (HDR vs normalized). Our

method is also unique in making systematic use of a technique for

representing color space and index data using a fractional number

of bits. This technique has many applications and is a key feature

of our work.

Wennersten and Str¨om [2009] describe a 2bpp format that makes

use of a fractional-bit encoding scheme to store indices in the range

[0::2] at a rate of 1.5 bits per index. Our method provides comparable

efficiency for this case, but is easier to generalize to other

non-power-of-two index sets, and does not limit the combinations

of indices that can occur.

奇

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晃晃

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tc

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C.R.CAN

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奇

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晃晃

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