Abstract: Three or more conversion functions are prepared. Only a part of the conversion functions are extracted therefrom to specify provisional conversion functions. A reference solid-pixel number and imaginary solid-pixel numbers for each provisional conversion function are computed through an imaginary exposure for a quarter halftone-dot block on a scanning line. The imaginary solid-pixel numbers are computed in response to new image signals which are obtained by converting an image signal through the respective provisional conversion functions. Then, each of the imaginary solid-pixel numbers is compared with the reference solid-pixel number, thereby a most-approximate conversion function, which gives a solid-pixel number most approximate to the reference solid-pixel number, is selected among the conversion functions.

Abstract: A structure of a system for automatically controlling a vehicle speed to a desired cruise speed is disclosed in which, when a signal generated by a cancel switch provided for halting a control operation of the system, is generated by a turning on of the cancel switch, a voltage applying portion, intervened between the cancel switch and each signal lines connected between one of set/coast switch and acceleration/resume switch and a corresponding input end of a control circuit, generates a voltage whose level is different from that generated when either set/coast or acceleration/resume switch is operated, the voltage being supplied to each of the signal lines. A signal generating portion provides a third signal in response to the applied voltage from the voltage applying portion to another input end of the control circuit.