Car navigation system

摘要

A navigation system includes a GPS receiver. Detection is made as to a number of GPS radio signals received by the GPS receiver. A display is operative for indicating a picture. At least one of a color tone and a luminance of the picture indicated by the display is controlled in response to the detected GPS radio signal number. Calculation may be made as to a rate of a decrease in the GPS radio signal number. In this case, at least one of the color tone and the luminance of the picture indicated by the display is controlled in response to the calculated decrease rate.