A method of producing an image signal based on light from a subject, where an optical unit passes light therethrough, an image pickup element has a light receiving side and an on-chip micro-lens arranged on the light receiving side to receive light passing through the optical unit, and a diaphragm having an adjustable opening which limits the amount of light received by the image pickup element from the optical unit in accordance with the size of the opening, the method comprising:
- passing light from the subject through the optical unit;
- receiving the light passing through the optical unit on the light receiving side of the image pickup element, the image pickup element producing an image signal from the received light, the image signal having corresponding color excitation values;
- and
- adjusting the ratio of the color excitation values of the image signal in correspondence with the size of the opening in the diaphragm.