Error with black and white images

Dear jhawksley,

Sorry to bother you but i’m afraid i really need some help,
I’m building a photography portfolio which went fluently thanks to your great theme so thanks for that!

The problem i’m encountering occurs while uploading black and white images. When i save them like i saved all of my other (colour) images (Photoshop->save for web->PNG-24) the images appear extremely dark on the website (very high contrast). This happened to every monochrome image so far, so i uploaded some of them in .jpeg format. The contrast seems so to be okay in .jpeg but the loss of detail makes the images not worth showing them.

Hope to hear from you soon and thanks in advance!

Kind regards,
Oliver