Board Thread:Support Requests - Getting Started/@comment-27667700-20170324081918/@comment-1073922-20170327193810

This is unrelated to image compression or file format. Wikia does not support screens that have high pixel densities like the MacBook Pro/iMac and iPhone's Retina displays. They look better than normal screens, but require websites to serve images that are twice the size they normally would be. Here's a link to an Apple Developer page on the topic.

Wikipedia's images look sharp because it has the $wgResponsiveImages setting enabled, which outputs three different thumbnails for each image to cater to 1x, 1.5x, and 2x displays. If you right click on any image on Wikipedia and choose "Inspect Element", you can see the  that produces it.

Considering 89% of iOS devices and 87% of Android devices have hiDPI displays, this seems like it should be a major priority, but I've never seen it mentioned in any of Wikia's "modernization" blogs.