April 2020
Intermediate to advanced
210 pages
4h 47m
Chinese
Content preview from 数据压缩入门
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83
第 7 章
字典转换
虽然信息论的创立是在
20
世纪
40
年代，哈夫曼编码的提出是在
20
世纪
50
年代，而互联网
的出现在
20
世纪
70
年代，但是直到
20
世纪
80
年代，数据压缩才真正引起了人们的兴趣。
随着互联网的快速发展，人们分享的内容已不再局限于文字，而是开始分享比文本大得多
的照片以及其他格式的数据。同时这种分享又发生在网络带宽有限、存储昂贵的时期，数
据压缩因此成了缓解这些瓶颈的关键。
随着移动设备正日益成为人们访问互联网的首选，实际上我们今天还是遇到
了同样的瓶颈。
虽然
VLC
一直都在发挥作用，但它与熵绑定的事实也限制了数据压缩未来的发展。因此，
当大多数研究人员在尝试寻找更有效的
VLC
技术时，
1
也有少数研究人员选择了不同的路，
他们找到了使统计压缩可以更有效地预处理数据的新方法。
这种新方法通常被称为“字典转换”（
dictionary transforms
），它完全改变了人们对数据压
缩的认知。突然间，压缩变成了一种对各种类型的数据都有用的算法。它的应用范围非常
广泛，事实上今天所有的主流压缩算法（比如
GZIP
或者
7-Zip
）都会在核心转换步骤中使
用字典转换。下面来具体看一看。
注
1
：
严格来说，只
Peter Elias
一个人就提出了
30
多种
VLC
技术。
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.