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电子信息类专业英语
第二版
李白萍主编
第十七单元
B
译文
Passage B
Compression/Decompression Techniques
压缩
/
解压缩技术
Numerous methods have been developed
for the compression of digital image
data.
One
of
the
principal
drivers
for
this
development
is
the
television
industry
where
quality
image
data
must
be
transferred
to
receivers
using
relatively
simple
equipment.
The
development
of
high
definition
television
is
further
focusing
the
attention of industry
and university scientists toward problems of data
reduction and
digital transmission. The
principal evaluation criteria for the analysis of
compressed
versus uncompressed imagery
is whether a person can tell the difference
between
the
images.
A
more
implemental
measure
is
the
Root
Mean
Square
(RMS)
error
between the original
image and the image that has been compressed.
Compression
rates may be generated by
determining the size of the compressed image in
terms of
number of bits per image pixel
for the original image.[1]
数字图像数据的压缩的许多
方法已经开发出来。为这项发展一个主要的驱
动是电视产业，
它
的质量图像数据必须使用相对简单的设备传输到接收器。
高清
电
视的发展进一步使产业和大学的科学家集中注意在减少数据和数字传输的问
题。
对于压缩和未压缩图像的分析的主要评估标准是一个人是否可以区分图像不
同之处。
更有帮助的措施是原始图像和图像压缩之间的均方根
(RMS)
错误。
压缩
率可能是由确定
大小的压缩图像以原始图像的每个图像像素的比特数形式表现。
[1]
Here
we
only
considers
compression
of
single
high
resolution
multi-spectral
images.
Higher
compression
rates
will
be
achieved
in
a
motion
sequence
where
frame to frame variations may be
quantified and only the changes from a reference
image need be coded.
这里我们只考虑
压缩单一的高分辨率多光谱图像。更高的压缩率将在帧到
帧之间的运动序列变化中量化和
只有从一个需要进行编码的参考图像的更改达
到。
There are two general types of
compression: (1) loss-less, and (2)
loss. Loss-less
compression
means that you can achieve a certain compression
factor and be able to
exactly
reproduce
the
original
image.
Loss
compression
on
the
other
hand
allows
some
loss, but has the potential for much higher
compression rates. No matter what
technique that you use, the exact rate
is very dependent on the complexity of the
image
that
you
are
analyzing.
For
example,
the
normal
best
that
can
be
achieved
with loss-less encoding in a rate of 2
bits per pixel. In fact, for some Land-sat scenes
with urban areas and many small farms,
the factor of 2 bits per pixel may not be able
to achieved. The same technique applied
to a Land-sat image of the mid-west where
large
fields
occur
and
few
shadows
exist
in
images
might
produce
a
much
better
compression.
< br>一般有两种类型的压缩
:(1)
无损压缩
,
和
(2)
有损。
无损压缩意味着你可以实现
一定的压缩因素并且能够完全还原原始图像。另
一方面损失压缩允许一些损失
,
但拥有潜在的更高的压缩率。不
管你使用什么技术
,
精确率是非常依赖于你分析
的图像的复杂度。例如
,
正常可以实现最好的无损编码
率是
2
位
/
像
素。事实上
,
对于一些城市地区和许多小农场的卫星遥感图像<
/p>
,2
位
/
像素的
因素可能无法实
现。同样的技术应用于西部的大油田的遥感图像
,
而且很少在可能产生更好的压
缩的图像中存在一点阴影。
One
loss-less
technique
is
known
as
run
length
encoding.
The
compression
algorithm
processes
each
line
of
input
imagery
looking
for
regions
in
which
data
values
are the same. If ten pixels in the original image
have a value of 10, then the
same data
may be represented as a data value, 10, and a
multiplier saying how many
times
the
value
is
repeated
before
a
changed
value.
Huffman
encoding
follows
a
similar
process.
These
loss-less
techniques
are
generally
called
entropy
coding
techniques, and have
application in document imaging, desktop
publishing, and GIS.
It
should
be
noted
that
entropy
coding
does
not
work
exceptionally
well
in
the
representation of remote sensing
images.
一个无损技术被称为运行长度编码。
压缩算法
流程处理输入图像的每一行去