JPEG2000标准详解：压缩与码流语法
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收藏 507KB PDF 举报 "JPEG2000标准详细讲解，包括其码流语法和文件格式，源自ISO/IEC JTC1/SC29/WG1，由Michael D. Adams撰写，项目为JPEG2000，公开发布，联系人是ISO/IEC JTC1/SC29/WG1的召集人Daniel T. Lee。"
JPEG2000（Joint Photographic Experts Group 2000）是图像压缩领域的一个重要标准，是对传统JPEG（Joint Photographic Experts Group）标准的升级。它于2000年被国际标准化组织（ISO）和国际电信联盟（ITU）联合发布，因此得名。JPEG2000旨在提供更高效、更灵活的图像编码方法，同时支持无损和有损压缩，适用于各种应用场景，如数字摄影、医学成像、遥感图像等。
JPEG2000的核心技术包括：
1. **离散小波变换（DWT）**：与JPEG中的离散余弦变换（DCT）不同，JPEG2000采用离散小波变换进行图像分解，将图像数据分解成多个频域分量，这种分解方式可以更好地捕捉图像的空间细节和频率信息。
2. **多分辨率表示**：JPEG2000支持多尺度表示，允许在不同分辨率下对图像进行处理和传输，这对于缩放和浏览非常有用。
3. **区域编码（Region-of-Interest Coding）**：用户可以根据需要优先编码图像的某些部分，例如，对图像的重要区域进行更高质量的编码，而其他区域则采用较低的压缩率。
4. **代码流语法**：JPEG2000的码流结构允许数据分块传输和解码，每个块可以独立处理，这使得网络传输和部分图像解码成为可能。码流包含一系列编码单元（Code Stream Segments），每个单元都包含图像的一部分信息。
5. **有损和无损压缩**：JPEG2000支持两种模式，有损压缩牺牲一定的图像质量来实现更高的压缩比，而无损压缩则不改变原始数据，适合对图像质量要求较高的场景。
6. **颜色空间处理**：JPEG2000标准支持多种颜色空间，如RGB、YCbCr等，并且提供了色彩管理机制，能够更好地处理不同设备间的色彩一致性问题。
7. **JP2文件格式**：JPEG2000的文件格式称为JP2（JPEG 2000 Part 2），是一种基于XML的开放标准，包含了图像元数据和压缩图像数据。此外，还有用于传输的JPX（JPEG 2000 Part 10）格式和更简单的J2K（JPEG 2000 Codestream）格式。
JPEG2000的这些特性使其在很多方面优于传统的JPEG标准，尤其是在网络传输、图像质量控制和灵活性方面。然而，由于其复杂的编码过程和相对较高的计算需求，JPEG2000在某些应用中并未完全取代JPEG，特别是在低功耗设备和对实时性要求较高的场合。
2 Copyright
c
2002–2005 Michael D. Adams
Part 1 (i.e., [7]) of the standard as the baseline codec. The base-
line codec is simply the core (or minimal functionality) JPEG-
2000 coding system. Part 2 (i.e., [15]) describes extensions to
the baseline codec that are useful for certain “niche” applica-
tions, while Part 3 (i.e., [16]) defines extensions for intraframe-
style video compression. Part 5 (i.e., [17]) provides two refer-
ence software implementations of the Part-1 codec, and Part 4
(i.e., [18]) provides a methodology for testing implementations
for compliance with the standard. In this paper, we will, for the
most part, limit our discussion to the baseline codec. Some of
the extensions included in Part 2 will also be discussed briefly.
Unless otherwise indicated, our exposition considers only the
baseline system.
For the most part, the JPEG-2000 standard is written from the
point of view of the decoder. That is, the decoder is defined quite
precisely with many details being normative in nature (i.e., re-
quired for compliance), while many parts of the encoder are less
rigidly specified. Obviously, implementors must make a very
clear distinction between normative and informative clauses in
the standard. For the purposes of our discussion, however, we
will only make such distinctions when absolutely necessary.
III. JPEG-2000 CODEC
Having briefly introduced the JPEG-2000 standard, we are
now in a position to begin examining the JPEG-2000 codec in
detail. The codec is based on wavelet/subband coding tech-
niques [21, 22]. It handles both lossy and lossless compres-
sion using the same transform-based framework, and borrows
heavily on ideas from the embedded block coding with opti-
mized truncation (EBCOT) scheme [23–25]. In order to fa-
cilitate both lossy and lossless coding in an efficient manner,
reversible integer-to-integer [26–28] and nonreversible real-to-
real transforms are employed. To code transform data, the codec
makes use of bit-plane coding techniques. For entropy coding,
a context-based adaptive binary arithmetic coder [29] is used—
more specifically, the MQ coder from the JBIG2 standard [30].
Two levels of syntax are employed to represent the coded image:
a code stream and file format syntax. The code stream syntax is
similar in spirit to that used in the JPEG standard.
The remainder of Section III is structured as follows. First,
Sections III-A to III-C, discuss the source image model and
how an image is internally represented by the codec. Next, Sec-
tion III-D examines the basic structure of the codec. This is
followed, in Sections III-E to III-M by a detailed explanation of
the coding engine itself. Next, Sections III-N and III-O explain
the syntax used to represent a coded image. Finally, Section III-
P briefly describes some of the extensions included in Part 2 of
the standard.
A. Source Image Model
Before examining the internals of the codec, it is important to
understand the image model that it employs. From the codec’s
point of view, an image is comprised of one or more compo-
nents (up to a limit of 2
14
), as shown in Fig. 1(a). As illustrated
in Fig. 1(b), each component consists of a rectangular array of
samples. The sample values for each component are integer val-
ued, and can be either signed or unsigned with a precision from
Component 1
Component 2
...
Component 0
Component N−1
(a)
Component i
...
...
...
(b)
Fig. 1. Source image model. (a) An image with N components. (b) Individual
component.
1 to 38 bits/sample. The signedness and precision of the sample
data are specified on a per-component basis.
All of the components are associated with the same spatial ex-
tent in the source image, but represent different spectral or aux-
iliary information. For example, a RGB color image has three
components with one component representing each of the red,
green, and blue color planes. In the simple case of a grayscale
image, there is only one component, corresponding to the lu-
minance plane. The various components of an image need not
be sampled at the same resolution. Consequently, the compo-
nents themselves can have different sizes. For example, when
color images are represented in a luminance-chrominance color
space, the luminance information is often more finely sampled
than the chrominance data.
B. Reference Grid
Given an image, the codec describes the geometry of the var-
ious components in terms of a rectangular grid called the ref-
erence grid. The reference grid has the general form shown
in Fig. 2. The grid is of size Xsiz × Ysiz with the origin lo-
cated at its top-left corner. The region with its top-left corner at
(XOsiz,YOsiz) and bottom-right corner at (Xsiz− 1, Ysiz − 1)
is called the image area, and corresponds to the picture data to
be represented. The width and height of the reference grid can-
not exceed 2
32
− 1 units, imposing an upper bound on the size
of an image that can be handled by the codec.
All of the components are mapped onto the image area of
the reference grid. Since components need not be sampled at
the full resolution of the reference grid, additional information
is required in order to establish this mapping. For each com-
ponent, we indicate the horizontal and vertical sampling period
in units of the reference grid, denoted as XRsiz and YRsiz, re-
spectively. These two parameters uniquely specify a (rectangu-
lar) sampling grid consisting of all points whose horizontal and
vertical positions are integer multiples of XRsiz and YRsiz, re-
spectively. All such points that fall within the image area, con-
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