A signal processor converts an input 3D image signal into a signal in which a left-eye signal and right-eye signal are rearranged temporally alternately. The gate signal includes a gate-on voltage for turning on the switching element and a gate-off voltage for turning off the switching element. The first output gear includes a first toothless portion that does not mesh with teeth of the input gear when the input gear is adjacent the first toothless portion. A default data type may be defined for data items not being uniquely classifiable.