Image reading apparatus, image forming apparatus, and method of image reading using wavelength distribution control unit to produce plural durations each having different peak wavelength in each main scanning

摘要

An image reading apparatus includes a light-emitting device having a peak wavelength that varies depending on a value of a drive current, and illuminates a document with illumination light from the light-emitting device. A light receiving unit receives a light reflected from the document when the illumination light is emitted from the light-emitting device, and converts the received reflected light into image data at a predetermined sensitivity depending on the wavelengths of the received light. A current drive circuit supplies the drive current to turn on the light-emitting device. A wavelength distribution control unit produces two or more durations each having a different value of the drive current by controlling the current drive circuit during each main scanning to the document to produce two or more durations each having a different peak wavelength in each main scanning.

主权项

1. An image reading apparatus comprising:
a light source unit which includes a light-emitting device having a characteristic that peak wavelength varies depending on a value of a drive current, and illuminates a document with an illumination light using light from the light-emitting device; a light receiving unit for receiving a reflected light reflected from the document when the illumination light is emitted from the light source unit, and for converting the received reflected light into an image data at a predetermined sensitivity depending on the wavelengths of the received light; a current drive circuit for supplying the drive current to the light-emitting device to turn on the light-emitting device; a storage unit for previously storing a wave pattern that represents the relationship between a current value for the drive current and time during which the drive current is produced relative to a line period corresponding to a scanning period for one line of the document in a main scanning direction, and that has two or more durations each having a different value of the drive current in the line period; and a wavelength distribution control unit for producing two or more durations each having a different value of the drive current by controlling the current drive circuit during the main scanning in each main scanning to the document by using the wave pattern read from the storage unit to produce two or more durations each having a different peak wavelength in each main scanning.