1. A method of liquid penetrant testing, comprising the steps of: illuminating a surface of a sample to be inspected with polarized light; picking up an image of the surface illuminated with the polarized light by a color camera; processing said image picked up in the obtaining step; storing an image processed in the processing step in a memory; and displaying said image stored in said memory, wherein, in the step of obtaining, said image of said surface is picked up by said color camera over plural visual field, wherein, in the step of processing, said image is processed by calibrating said image by using a parameter which is calculated from data of an image of a color chart for calibration which contains white, red and plural colors between white and red picked up by said color camera.