All page header image makes my photo go darker

Hi there, I am using the theme: STOUT, on the header for each page is one photo of my choice. The photo is nice and bright and colourful but once I select me picture and it saves in the header the system makes the picture much darker than the original, can this be changed as I would like the picture to be as it was? Any help would be greatly appreciated, thank you.

The page I need help with: [log in to see the link]