Image reading apparatus

An image reading apparatus comprising:

• a sheet table comprising a placement surface on which a sheet is placed;
• a light emitting device comprising a plurality of light sources, each of which emits different color light from one another;
• a light emitting unit, which comprises a plurality of light emitting devices, and which emits light to the placement surface;
• a light receiving unit that receives reflected light from the placement surface;
• a read image conversion unit that converts the reflected light into read image information;
• a pulse signal output unit that outputs a pulse signal of a period corresponding to a time for converting into the read image information of one line as a minimum unit for converting into the read image information by the read image conversion unit from the reflected light of each of the plurality of light sources;
• a plurality of drive current supply units that supply drive currents, each of which is a constant current, to respective one of the plurality of light emitting devices;
• a light emission control unit that is configured to:
• control the light sources to emit the same color lights among the plurality of light emitting devices for each period,
• switch the light sources from emitting first color lights by first color light sources to emitting second color lights by second color light sources among the plurality of light emitting devices for each period in sequence in synchronization with the pulse signal;
• and
• control the second color light sources to emit the second color lights based on a current value determined for each of the plurality of light emitting devices and a light emission time for each of the plurality of light sources during the period;
• a first light emission parameter determination unit that is configured to:
• select a smallest light source, in which a light amount required for converting into the read image information is the smallest among the plurality of light sources, from the plurality of light sources;
• control the smallest light source to emit light throughout the period;
• determine the current value required for obtaining at least the required light amount based on the emit light by the smallest light source;
• determine the determined current value as the drive current value of a first light emitting device having the smallest light source;
• and
• determine the light emission time of each of the plurality of light sources of the first light emitting device for enabling each of the plurality of light sources of the first light emitting device to emit the light throughout the period;
• and
• a second light emission parameter determination unit that determines a drive current value of a second light emitting device and the light emission time of each of the plurality of light sources of the second light emitting device such that a sum of a first light amount and a second light amount becomes the light amount required for converting into the read image information during the period, wherein:
• the first light amount is a light amount of light emitted from each of the plurality of light sources of the first light emitting device in the drive current value determined by the first light emission parameter determination unit;
• and
• the second light amount is a light amount of light, which is emitted from the light source of the second light emitting device and which is the same color as the light emitted from each of the plurality of light sources of the first light emitting device, received by the light receiving unit,
• wherein the light emission control unit controls the plurality of light sources to emit the same color light in sequence based on the drive current value of each of the first light emitting device and the second light emitting device and the light emission time of each of the plurality of light sources determined by the first light emission parameter determination unit and the second light emission parameter determination unit.