WebPageTest, PageSpeed, LightHouse image compression analysis methods

What are the analysis methods they used to give us suggestions about image compressions.

WebPageTest/ PageSpeed/ LightHouse

WebPageTest

• The author said: mozjpeg with quality = 85%.

• Or you could check out the code here:

webpagetest/agent/wpthook/mozjpeg at master · WPO-Foundation/webpagetest · GitHub

• http://www.webpagetest.org/jpeginfo/jpeginfo.php?url=https://static-sg.zacdn.com/cms/fpseason/27th/Soft_Utility_Hero_Segment_27Feb.jpg

Google PageSpeed

• The recommended size is similar to WebPageTest.
• They use libjpeg.

page-speed/jpeg_optimizer.cc at master · pagespeed/page-speed · GitHub

• Default configuration COULD be 85.

ImageRecompressionQuality

This option sets the quality for JPEG and WebP formats. It can be overridden by any format-specific or application-specific quality. The default is 85.

Image Filter and Option Reference

LightHouse

Use Canvas API with quality = 0.8.

lighthouse/optimized-images.js at master · GoogleChrome/lighthouse · GitHub

HTMLCanvasElement.toDataURL()

Read more about the PR

feat(DBW): add audit for detecting unoptimized images by patrickhulce · Pull Request #1452 …

The code quality of this project looks much better than WebPageTest, lol.