Where Are Pixels? -- a Deep Learning Perspective

Technically, an image is a function that maps a continuous domain, e.g. a box , to intensities such as (R, G, B). To store it on computer memory, an image is discretized to an array array[H][W], where each element array[i][j] is a pixel.

How does discretization work? How does a discrete pixel relate to the abstract notion of the underlying continuous image? These basic questions play an important role in computer graphics & computer vision algorithms.

This article discusses these low-level details, and how they affect our CNN models and deep learning libraries. If you ever wonder which resize function to use or whether you should add/subtract 0.5 or 1 to some pixel coordinates, you may find answers here. Interestingly, these details have contributed to many accuracy improvements in Detectron and Detectron2.

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Deep Learning Experiments and Claims

这几年来, 从 FAIR 的几位大佬身边学习到的最多的是对待 research 的态度. 因此说说写 paper 和做实验的体会.

实验与 claims

实验是为了证明或强化文章里给出的 claim/hypothesis 的.

Ross ICCV 2019 tutorial 最后谈了谈怎么写 paper. 第 126 页说, 文章中所有的 claim, 理想情况下都应该要么是文献中已有的 claim, 要么是有实验能够证明的 claim.

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Unawareness of Deep Learning Mistakes

TL;DR: People are hardly aware of any deep learning mistakes they made, because things always appear to work, and there are no expectations on how well they should work. The solution is to try to accurately reproduce settings & performance of high-quality papers & code.

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About Research

这个领域里, 什么都特别快.

三个月前看到 Bengio 组的 BinaryConnect. 脸草的同事都很喜欢模型加速 / 压缩的主题, 因此立刻就重现了结果开始改进. 当时就说要做成 Binary Activation, 并且搞一个 GPU runtime. 正当同事们回家过年, 我在 yy 这学期 parallel 大作业要不就写这个 runtime 的时候, 昨天看到 Bengio 新的 paper 挂出来, 已经都做完了. 更夸张的是, 在前天 arxiv 挂了另一篇文章, 方法基本一样.

三个月, 能专心做的话并不难, 然而我要应付作业, 要去 oculus 写代码, 还有其他好玩的东西在分心. 想着有空慢慢做的时候, 别人已经不等你了.

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