Reading/Web/Lazy loading of images on Japanese Wikipedia

On Tuesday 5th July lazy loaded images was enabled on Japanese Wikipedia for all users. The immediate impact we noticed images on Japanese Wiki Japan article served to users dropped 1.443mb to 142kb.

Bytes saved
The bytes saved varies per article. Articles with more images obviously will be reduced more. We can analyze bytes saved by looking at raw access logs and looking at images with an internal referrer. We can also look at specific pages to gauge impact.

Analysis of weeks worth of data
On 12th July a database dump of the EventLogging data for Japanese Wikipedia was taken from the period 1st June to 12th July. Data before the change and after the change was compared. Given the change was deployed on 5th July at 4:47pm PST data for the week preceding the timestamp 20160706004700 was compared with data after for the mobile web stable channel. The goal was to sanity check whether the change had been positive or negative so it should be noted that little care was taken to give these results scientific merit. The before sample was roughly 3 weeks compared to a 1 week after sample.