April 2019
Intermediate to advanced
172 pages
4h 39m
Chinese
Content preview from 精通特征工程
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.
自动特征生成：图像特征提取和深度学习
｜
117
8.3
通过深度神经网络学习图像特征
要定义良好的图像特征，
SIFT
和
HOG
还有很长一段路要走。然而，计算机视觉领域的最
新成果则来自于另外一个非常不同的方向：深度神经网络模型。这一突破发生在
2012
年
的
ImageNet
大规模视觉识别竞赛（
ILSVRC
）中，当时来自多伦多大学的一群研究者几
乎将前一年优胜者的错误率降低了一半。他们称其所使用的方法为“深度学习”，以强调
这种方法不同于以前的神经网络模型，而是包括很多叠加在一起的神经网络层和转换层
的最新一代模型。
ILSVRC 2012
的优胜模型——后来被称为
AlexNET
，以它的首席发明
者命名——有
13
层（
Krizhevsky
等，
2012
），
ILSVRC 2014
的获胜者
GoogleNet
有
22
层
（
Szegedy
等，
2014
）。
从表面上看，堆叠神经网络的机制似乎与
SIFT
和
HOG
的图像梯度直方图相去甚远。但从
AlexNet
的可视化可以看出，它的最初几层本质上就是计算边缘梯度和其他一些简单模式，
与
SIFT
和
HOG
非常相似。随后的几层将局部模式组合成更全局化的模式。最终结果是一
个特征提取器，比以前的提取器要强大许多。
堆叠神经网络层（或任意其他分类模型）这种模式并不是什么新的思想，但训练这种复杂
模型需要大量的数据和计算能力，这是近期才具备的。
ImageNet
数据集中有
120
万张标
记好的图像，类别有
1000
个。现代
GPU
大大加快了矩阵
-
向量计算，很多机器学习模型
（包括神经网络）的内核就需要这种计算。深度学习方法的成功就依赖于可使用大量数据 ...
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.