Image reading device, image forming apparatus, and shading data processing method

An image reading device comprising:

• a first image reading unit movable between a first area facing a document transport path and a second area not facing the document transport path, and configured to read, in the first area, a first surface of a document transported on the document transport path;
• a second image reading unit disposed in the first area and configured to read a second surface of the document;
• a first shading reference member facing the first image reading unit at a first distance therefrom when the first image reading unit is located at a second position in the second area, wherein the first image reading unit is configured to read the first shading reference member to acquire first shading data;
• a second shading reference member facing the first image reading unit at a second distance therefrom across the document transport path when the first image reading unit is located at a first position in the first area, wherein the first image reading unit is configured to read the second shading reference member to acquire second shading data;
• a third shading reference member facing the second image reading unit at the second distance therefrom across the document transport path, wherein the second image reading unit is configured to read the third shading reference member to acquire third shading data;
• and
• a controller comprising a memory storing computer-readable instructions and a processor configured to execute the computer-readable instructions to correct an error in the third shading data, resulting from a distance from the second image reading unit to the third shading reference member being different from a distance from the second image reading unit to the document transported on the document transport path, by,
• determining a difference between the first shading data and the second shading data,
• correcting the third shading data based on the difference between the first shading data and the second shading data to acquire corrected third shading data,
• comparing a maximum value of the corrected third shading data with a threshold value, and
• adjusting, in response to the maximum value of the corrected third shading data being outside a tolerance range of the threshold value, a light amount of a light source of the second image reading unit to set the maximum value of the corrected third shading data within the tolerance range of the threshold value, whereby the maximum value of the corrected third shading data is adjusted to a maximum value of the first shading data.