Image compression work-around?

I’m trying to use an eye-catching image on my home page (copperpeak.com) and WordPress seems to keep compressing it to the point that the colors are washed out and the image is no longer the great first impression I need. When I look at the file in my media directory it looks great, but when it displays on my live site it looks blah.

I read online that I could add the following to the theme functions.php file to correct this:

add_filter(‘jpeg_quality’, function($arg){return 100;});

I did that and it doesn’t seem to have improved the look of my image. Is there anything else I can do?