Background filters affect the way the background (imported image) is displayed behind the drawn vector objects. Characteristics such as Brightness, Contrast, Gamma and colors Saturation can be adjusted in this window.
In contrast to graphics programs where the main meaning of filters is to enhance the look of an image, filters in Mapwel are intended for dimming, darkening, brightening or other adjustment of image so that its colors do not interfere with objects drawn on top of the background image. All these parameters are saved with map into a single MPW file.
Gamma parameter changes brightness mostly of dark colors and it does not affect absolute black and white.
None of above settings affects the map appearance in the GPS. They only serve to make map drawing more comfortable.