A method and a portable device controls output of a display unit to display information accurately and clearly regardless of a background image. Disclosed is an arrangement for calculating a difference between an arbitrary expression value of an arbitrary screen configuration element to be displayed on a given area of the background image and an actual expression value of the given area of the background image. Each expression value includes at least one of a color and lightness. The arrangement automatically selects the expression value of the screen configuration element based on the calculation result. The screen configuration element is displayed at the given area of the background image based on the selected arbitrary expression value.