Image reading device with cover status detector

摘要

A reference surface for determining a threshold level of an image sensor is provided on a guide plate swingable with a cover away from the image sensor. The reference surface has markings thereon for determining a reading range of the image sensor. The image reading device makes three detections from the reading of the reference surface: a detection of the cover position by detecting the presence of the markings; a detection of the reading range of the image sensor by detecting the arrangement of the markings; and a detection of the threshold level of the image sensor by detecting the background of the reference surface. The threshold level is not taken until the device has determined that the cover is closed.