The present technology relates to a signal processing device and a method, an imaging device, and an imaging apparatus that are designed to reduce occurrences of A/D conversion errors. A signal processing device of the present technology includes: a comparing unit that compares an analog signal output from a unit pixel with a predetermined voltage; a switching unit that switches reference voltages to be supplied to the comparing unit as necessary, connects one of the reference voltages to the comparing unit, and connects another one of the reference voltages to a predetermined load capacitance, the reference voltages being of different gradation accuracies from each other; and a measuring unit that measures timing of a change in a result of the comparison performed by the comparing unit. The present technique can be applied to imaging devices and imaging apparatuses, for example.