A signal conversion apparatus which converts an input signal x from an image sensor into an output signal y by a function relation represented by Expression 1: y = f ⁡ ( x ) = ∫ b x ⁢ [ 1 / r ⁡ ( ξ ) ] ⁢ ⅆ ξ ( 1 ) where b is a predetermined constant, ξ is an integration variable corresponding to a value of the input signal x, and r(ξ) is a quantization step function before removal of a noise of the input signal x, which determines an increment of the input signal x to an increment of the output signal y.