Image reader and image forming apparatus including same

An image reader comprising:

• a contact glass that is fixed to an upper surface of a scanner frame and divided into a manual document reading glass and an automatic document reading glass;
• an automatic document feeder that is openable and closable with respect to the contact glass in an up-down direction and conveys a document sheet to an upper surface of the automatic document reading glass;
• a first reading module
• that is disposed below the contact glass so as to be reciprocatable in a sub scanning direction,
• that is capable of reading an image on a front side of a document sheet laid on the manual document reading glass while moving in the sub scanning direction, and
• that is also capable of reading an image on a front side of a document sheet conveyed to the upper surface of the automatic document reading glass while remaining stationary at a reading position that faces the automatic document reading glass;
• a second reading module that is disposed inside the automatic document feeder, and capable of reading an image on a back side of a document sheet conveyed to the upper surface of the automatic document reading glass;
• and
• a controller that determines whether it is necessary for the first reading module to reacquire the black reference data or the white reference data,
• wherein
• the first reading module and the second reading module each includes a light source and a sensor that reads, as image light, reflection light of light emitted from the light source, the first reading module and the second reading module being each capable of performing shading correction in which black reference data is acquired through reading performed by the sensor with the light source turned off, and white reference data is acquired through reading performed by the sensor at a position facing a white reference plate, with the light source turned on,
• in a case of performing continuous one-side reading in which the first reading module continuously reads images on front sides of document sheets conveyed to the upper surface of the automatic document reading glass by the automatic document feeder, during the continuous one-side reading the controller makes the second reading module perform reading with the light source turned off and outputs, as a dark output value, a sensor output value obtained in the reading, and
• the controller reacquires the black reference data of the first reading module when a variation amount of the dark output value with respect to a latest piece of the black reference data of the first reading module acquired immediately therebefore exceeds a predetermined value A1, and the controller first reading module reacquires both the black reference data and the white reference data of the first reading module when the variation amount of the dark output value with respect to the latest piece of the black reference data of the first reading module acquired immediately therebefore exceeds a predetermined value A2, the predetermined value A2 being larger than the predetermined value A1.