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PSI 和 SI 的区别 #19

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fengzilong opened this issue Jun 4, 2020 · 0 comments

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fengzilong commented Jun 4, 2020 •

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Perceptual Speed Index 是 Speed Index 的一个变种，PSI 使用了 SSIM（结构相似性）计算加载完成度

区别在于：

SI 会忽略加载过程中的抖动，PSI 则对加载过程中的布局抖动更敏感

比如首屏加载过程中，页面顶部出现一个广告条，把整体内容往下挤，导致布局发生变化，PSI 会变大，而 SI 则会忽略这种布局的不稳定性

最新版 lighthouse 用的是 Speed Index，原因在这个 PR 中有所描述

core(metrics): switch to speedIndex from perceptualSpeedIndex

参考：
https://www.webpagetest.org/forums/showthread.php?tid=14883&pid=29608#pid29608
https://sites.google.com/a/webpagetest.org/docs/using-webpagetest/metrics/speed-index
http://www.parvez-ahammad.org/blog/perceptual-speed-index-psi-for-measuring-above-fold-visual-performance-of-webpages
https://arxiv.org/pdf/1704.01220.pdf
GoogleChrome/lighthouse#785
GoogleChrome/lighthouse#4980

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