IMAGE READING DEVICE, IMAGE FORMING APPARATUS, AND EXTERNAL AREA DETERMINATION METHOD

PROBLEM TO BE SOLVED: To provide an image reading device, an image forming apparatus, and an external area determination method by which an external area outside a document area can be accurately determined with a low load in image data of a read document.SOLUTION: In a compound machine, a control unit executes external area determination processing. The control unit compares reference light intensity distribution data D ( ) stored in advance in an EEPROM with light intensity distribution data acquired by image reading in step S15 in terms of light intensities in areas on the same coordinates of both data, and when the light intensities coincide with each other, determines that the area of the light distribution data is an external area and converts the light distribution data in the external area into white image data.