While publishing a HTML5 application, I noticed it is possible to reduce image file size and improve load times by doing this:
- after building the HTML5 application (development mode), go in the 'resources' folder and select all png images
- drag and drop all png files to https://tinypng.com/ (or any other lossless compression service you prefer)
- replace the old png files with the new ones
By doing this I reduced file size of all images by an average 73%, with no visible quality loss and a significant faster load time
Hope it helps!