An imaging apparatus has an image pickup device having a plurality of pixels having input-output characteristic which non-linearly changes according to input and a plurality of color filters in a plurality of colors arranged on respective pixels; an output signal linear convertor converting a first output signal from the image pickup device into a second output signal which is predicted to be output from the image pickup device on the assumption that the image pickup device outputs the second output signal which linearly changes all over a range of the input brightness; a color signal generator generating color signals in the plurality of colors on each pixel based on the second output signal; a brightness signal generator generating a brightness signal from the first output signal; and a color brightness composition part combining the color signals and the brightness signal to generate an image signal.