I am seeking recommendations for Windows software that will automatically decrease the brightness of the desktop background image (wallpaper).
The backgrounds images are set to be shown as a slideshow by Windows.
The software needs to be gratis.
The software must be compatible with Windows 7. Compatibility with Windows 8, 8.1, and/or 10 is a plus, but not required.
I prefer open-source and portable software, but neither are hard requirements.