Patent ID: 8498030

Claim:
An image scanning apparatus comprising: an illumination unit having three light-emitting elements, each having different emission spectra from each other, configured to illuminate a document to be scanned in a linear pattern; a plurality of photoelectric conversion elements that convert light which is emitted by the illumination unit and is reflected by the document into electrical signals; an emission control unit that controls the light-emitting elements to have plural full light-ON periods in each of which all three light-emitting elements are turned on and three light-OFF periods in each of which a respective one of each of the three light-emitting elements is turned off, in a scan period; a light amount integrating unit that integrates the electrical signals converted by the photoelectric conversion elements during the plural full light-ON periods and three light-OFF periods each of which a respective one of each of the three light-emitting elements is turned off and outputs the integrated electrical signal as a light intensity of the scan period; a prediction unit that predicts an electrical signal corresponding to an amount of light value to be converted by the photoelectric conversion elements during all the light-emitting elements are turned on in the scan period, based on the electrical signals integrated by the light amount integrating unit during the plural full light-ON periods; and an arithmetic unit that calculates a difference between the integrated electrical signal integrated by the light amount integrating unit and the predicted electrical signal predicted by the prediction unit in the scan period and calculates a light intensity signal of each of the three light-emitting elements based on the difference in the scan period.