Image reading apparatus and image forming apparatus

An image forming apparatus comprising:

• a light emitting unit which emits light to a document;
• a photoelectric conversion unit which converts a quantity of light reflected from the document into an analog signal;
• an A/D converter which converts the analog signal into a digital signal;
• a clock unit which clocks an elapsed time from start-up of the light emitting unit which occurs upon a power supply being switched on;
• a memory including:
• a light-quantity correction table in which the elapsed time is corresponded to the quantity of light;
• and
• a γ correction table in which a digital signal is corresponded to a first correction value for carrying out γ correction for the digital signal,
• a light-quantity calculating unit which calculates the quantity of light emitted to the document from the light emitting unit on the basis of the clocked elapsed time from a time at which the clock unit starts clocking to a time at which the light emitting unit starts emitting the light by an operation of a user by referring to the light-quantity correction table;
• a correction value calculating unit which calculates a second correction value for the digital signal on the basis of the light quantity calculated by the light-quantity calculating unit and the digital signal;
• a γ correction unit which corrects the digital signal on the basis of the γ correction table, wherein the γ correction unit is configured to:
• convert the γ correction table on the basis of the second correction value calculated by the correction value calculating unit;
• and
• correct the digital signal on the basis of the converted γ correction table;
• and
• an image forming unit which forms an image on the basis of the corrected digital signal.