In a displacement sensor, an illumination optical system, which converts laser light emitted from an emission unit into first converging light, and irradiates with the first converging light a detection space through which a target moves. An imaging optical system converts laser light reflected from the target into second converging light, and irradiates with the second converging light a light-receiving surface of a detection unit. The image of the emission unit into which the illumination optical system focuses the first converging light is displaced along the optical axis of the imaging optical system by a temperature change of the illumination optical system. The range in which the image is displaced is limited to be located either anterior to the front principal point of the imaging optical system, or posterior to the rear principal point of the imaging optical system.

An image reading device includes a plate on which a document to be scanned is placed, a cover that is movable between an open position and a closed position at which the cover contacts the document, a position detecting unit configured to detect a position of the cover, an imaging unit configured to emit light towards the plate and having an image sensor configured to detect light reflected by the document, and a control unit configured to determine a size of the document based on a detection result of the position detecting unit and a detection result of the image sensor.

An image forming apparatus capable of preventing misdetermination of a type of printing paper includes a transmitted light receiver, a specularly reflected light receiver, and a diffusively reflected light receiver, which constitute a sensor, and an output determiner that determines whether data output by the plurality of light receivers is normal. The image forming apparatus determines the type of printing paper and an abnormality of the printing paper from the determination by the output determiner.

An image forming apparatus capable of preventing misdetermination of a type of printing paper includes a transmitted light receiver, a specularly reflected light receiver, and a diffusively reflected light receiver, which constitute a sensor, and an output determiner that determines whether data output by the plurality of light receivers is normal. The image forming apparatus determines the type of printing paper and an abnormality of the printing paper from the determination by the output determiner.

A printer that includes systems for detecting transparent medium may include a medium dispenser for transporting print medium along a transport pathway to a print station which receives the print medium. Transmitters and receivers may be positioned on opposite sides of the transport pathway for scanning the print medium with a light beam. The sensor arrangement may be configured to detect deflection of the light beam when a transparent print medium is transported on the transport pathway between the transmitter and the receiver. The results of the scan may be communicated to a controller to facilitate proper print settings.

An image scanning apparatus performs operations including: upon detection of a first angle, causing light to be emitted to an original and recording a distribution of reflected light of the emitted light as first read data; upon elapse of a predetermined time from detection of a second angle, causing light to be emitted to the original and recording a distribution of reflected light of the emitted light as second read data; detecting a closed state of a pressure plate based on the second read data; and upon determination of an angle of the pressure plate with respect to the platen being equal to or smaller than a third angle smaller than the second angle in the detection of the closed state, detecting a width of the original in an opening-closing direction of the pressure plate based on a difference between the first and second read data.

An image processing device includes circuitry configured to calculate an edge amount for the target pixel in a shadow region in image data; determine whether the target pixel corresponds to an edge, based on the edge amount; determine whether the edge is a part of a continuous edge based on the edge amount, in response to a determination that the target pixel corresponds to the edge; count an edge continuity number for the target pixel; count an edge continuity number for a previous target pixel selected immediately before the target pixel and determine whether the edge continuity number for the previous target pixel is greater than a preset number in response to a determination that the target pixel does not correspond to the edge; and detect a boundary position based on the edge amount of each of the target pixels forming the continuous edge up to the previous target pixel.