We run image optimisation through section.io and are seeing issues with images on our site. There are differences between the image from our web application and the image through the CDN. The original image is sharp but through the CDN it becomes blurry.
There are a number of reason that mod PageSpeed image optimisations could cause this.
Here are the common issues.
Mod Pagespeed will compress an image if it thinks the original is too large in bytes. You can toggle the level of compression using
pagespeed ImageRecompressionQuality 95;in the server config. See https://www.modpagespeed.com/doc/reference-image-optimize#ImageRecompressionQuality
Mod Pagespeed will resize an image if the original is larger than the displayed size. If the original is 1000x1000 pixels, but is marked with HTML attributes
height="400" width="400"then Pagespeed will resize that image according to the HTML attributes. Check the HTML to make sure that the
heightattributes are correctly set.
You can also toggle whether Pagespeed should resize an image if it is close to the original size to preserve clarity using
pagespeed ImageLimitResizeAreaPercent 45;See https://www.modpagespeed.com/doc/reference-image-optimize#ImageLimitResizeAreaPercent for details
Specific image compression settings
Mod Pagespeed allows you to set image compression for specific file types. e.g. https://www.modpagespeed.com/doc/reference-image-optimize#JpegRecompressionQuality
Make sure these settings are correct.