April 2020
Intermediate to advanced
210 pages
4h 47m
Chinese
Content preview from 数据压缩入门
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.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.
自适应统计编码
｜
81
解码器以相反的方式工作。给定当前的概率，找出与当前输出值对应的符号，然后更新概
率表，再重新分配各符号的区间。
增加字面值与重置词条后，其工作原理仍然与自适应
VLC
相同。我们可以将这些词条指
定为附加符号，并相应地调整它们的权重。
6.4
自适应哈夫曼编码
将哈夫曼编码变成自适应的不像算术编码那样简单，主要原因是哈夫曼树结构的处理比较
复杂。
考虑这一问题：为了正确地输出符号的码字，需要一棵完整的哈夫曼树。最简单的想法就
是，每遇到一个符号就去重新生成一棵完整的哈夫曼树。这一想法可以实现，但这样做会
极大地影响算法的性能。
因此，自适应哈夫曼算法没有每次都重新生成完整的树，而是在读取和处理符号时调整现
有的树。这就让情况变得稍微有些复杂，因为每读取一个符号都必须要做以下这些事情：
•
更新概率；
•
对树的大量结点变换位置并重新排序，以使它们与概率的变化同步；
•
使树的结构满足哈夫曼树的要求。
自适应哈夫曼算法的最初版本是由
Faller
7
于
1973
年提出的，
1985
年高德纳
8
又对此算法做
出重大改进，但是所有现代的版本都是建立在
Vitter
9
于
1987
年提出的方法之上。如果你想
深入研究，可以参阅脚注里提到的这些文献。
6.5
现代的选择
相比静态的方法，这些动态的改进有以下优点。
•
有生成符号码字对应表的能力，无须将符号码字对应表显式地存储在数据流中。数据流
变小后，计算性能就能有所提高，但更重要的是下面两个优点。
•
有实时压缩数据的能力，无须再将整个数据集作为一个整体来处理。这让我们可以有效 ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
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.