Visible quality loss from JPG to WEB

[Frederic Trudeau]

Hello again group.

See those two images.

Original : http://prospek-stage-20160519.ftrudeau.me/wp-content/uploads/2016/02/communauto-image-header_1200x600.jpg

Optimized : http://prospek-stage-20160519.ftrudeau.me/wp-content/uploads/2016/02/xcommunauto-image-header_1200x600.jpg.pagespeed.ic.9ow3nwp_10.webp

There is a visible quality loss in the optimized image.

How to make sure this does not happen ?

Thanks.

FT