A document size detection device includes: a light source to irradiate a document with light; an imaging device to receive light reflected at the document; and circuitry to control switch on and off of the light source and movement in a sub-scanning direction of the light source, and determine a size of the document based on image data acquired by the imaging device. The circuitry is to determine a size in a main-scanning direction of the document based on: first image data acquired when the light source is switched off while the light source is at a first reading position; second image data acquired when the light source is switched on while the light source is at the first reading position; and third image data acquired when the light source is switched on while the light source is being moved from the first reading position to a second reading position.

An optical scanning device includes a reflected-light passing unit having a passing region through which a portion of reflected light that is the scanning light reflected by the medium passes. An outer peripheral contour line of the passing region includes a contour curve configured with a set of points where coordinates in a direction orthogonal to a scanning direction are uniquely determined for the coordinates in the scanning direction. The contour curve renders a curve protruded toward the passing region. When a region in contact with the contour curve in the passing region is divided into a plurality of quadrilateral minute regions having equivalent areas and extending from the contour curve to a predetermined coordinate position in the scanning direction and are continuously arranged in the orthogonal direction, widths of the minute regions in the scanning direction are different for each location in the orthogonal direction.

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 optical device includes a light guiding unit that emits light to be guided to a predetermined position from a light emitting aperture, a detection unit that receives light reflected at the predetermined position, and a light blocking unit that includes a light blocking member located closer than an imaginary line to the detection unit in a cross section including the predetermined position and the light guiding unit, the imaginary line connecting the predetermined position and an end of the light emitting aperture that is far from the predetermined position in an optical axis direction.

An automatic document feeding system includes an image reader including an optical window and a light source illuminating the optical window, and an automatic document feeder including a reflective flag positioned within a viewing region of the optical window.

A reflected light amount from a patch under a first light source is acquired, and a reflected light amount from the patch under a second light source whose wavelength band is different from the first light source is acquired. The type of a printing medium on which the patch is printed is determined based on the ratio of the two acquired reflected light amounts.

A position detecting device includes an image sensor and circuitry. The image sensor is configured to read reflected light of light emitted from a light source onto a medium to be read. The circuitry is configured to perform black correction processing on an output signal of the image sensor using black correction data of the image sensor and detect a position of the medium from the output signal after the black correction processing.

In an information processing apparatus connected with an image forming apparatus having an image forming unit, the image forming unit includes a first receiver, a light source, a photosensitive member, a rotatable polygon mirror including a plurality of reflection surfaces, a light receiver configured to receive light, an identifier configured to identify a reflection surface to be used for scanning the photosensitive member, and a first outputter. The information processing apparatus includes a second receiver configured to receive the predetermined signal, a corrector configured to correct the image data with correction data corresponding to the reflection surface corresponding to each scan line based on the specific reflection surface, and a second outputter configured to start outputting the image data in response to start of reception of the predetermined signal.

An image processing apparatus includes: a conveyance unit configured to convey a medium; a sensor configured to sense a medium being conveyed; and a controller configured to control the conveyance unit and acquire a result of the sensing performed by the sensor. The sensor includes a light emitter, a light receiver configured to perform output in accordance with the amount of the received light, and a shielding unit including a transmissive part through which the sensing light transmits. The transmissive part has a shape in which an opening width in a direction orthogonal to a conveyance direction of the medium changes in the conveyance direction. The controller determines skewing of the medium being conveyed based on change in the amount of light received by the light receiver as the medium passes along the transmissive part and temporal change in accordance with the conveyance of the medium.

An image processing device includes: a fold unit that folds an adjustment sheet based on a predetermined reference fold position; a punch hole former that forms a punch hole in a stacked portion of the adjustment sheet, created as a consequence of folding of the adjustment sheet; an image reader that reads an image of the adjustment sheet with the adjustment sheet unfolded, in which the punch hole is formed; and a position identifying unit that identifies a position of a fold line using at least positions of a pair of punch hole images which appear in the image of the adjustment sheet and on both sides of the fold line of the adjustment sheet.