An image forming apparatus includes a first medium scanned with a first signal, a second medium scanned with a second signal, a rotary polygon mirror that deflects the first and second signals, a synchronization signal generation circuit that generates a synchronization signal representing a time to start scanning the first medium, and at least one pseudo synchronization signal generation circuit that generates a pseudo synchronization signal with the synchronization signal. The pseudo synchronization signal represents a time to start scanning the second medium. Based on a previously calculated period of the synchronization signal and a period of the synchronization signal counted on a particular surface of the polygon mirror, the pseudo synchronization signal generation circuit generates a particular value for generating the pseudo synchronization signal. Based on the particular value, the pseudo synchronization signal generation circuit starts generating the pseudo synchronization signal when the synchronization signal is enabled.

An image forming apparatus includes a first medium scanned with a first signal, a second medium scanned with a second signal, a rotary polygon mirror that deflects the first and second signals, a synchronization signal generation circuit that generates a synchronization signal representing a time to start scanning the first medium, and at least one pseudo synchronization signal generation circuit that generates a pseudo synchronization signal with the synchronization signal. The pseudo synchronization signal represents a time to start scanning the second medium. Based on a previously calculated period of the synchronization signal and a period of the synchronization signal counted on a particular surface of the polygon mirror, the pseudo synchronization signal generation circuit generates a particular value for generating the pseudo synchronization signal. Based on the particular value, the pseudo synchronization signal generation circuit starts generating the pseudo synchronization signal when the synchronization signal is enabled.

An image scanning device has a platen, an openable cover, a cover sensor, a scanning unit, a condition setting unit enabling a user to set a first condition, and a controller. The controller is configured to detect an opening state of the cover based on a detection signal output by the cover sensor and obtain the image data representing a partial image which is an image of a first end portion of a scannable area of the scanning unit. When the cover is in the closed state, the controller applies an image processing based on the first condition set through the condition setting unit, and when the cover is in the opened state, the controller applies the image processing based on a second condition which is a particular condition set in advance and different from the first condition.

An image scanning device has a platen, an openable cover, a cover sensor, a scanning unit, a condition setting unit enabling a user to set a first condition, and a controller. The controller is configured to detect an opening state of the cover based on a detection signal output by the cover sensor and obtain the image data representing a partial image which is an image of a first end portion of a scannable area of the scanning unit. When the cover is in the closed state, the controller applies an image processing based on the first condition set through the condition setting unit, and when the cover is in the opened state, the controller applies the image processing based on a second condition which is a particular condition set in advance and different from the first condition.

An optical scanning device deflects light for scanning in a main scanning direction and includes a plurality of light sources, a plurality of photodetectors, a plurality of optical element groups, and a polygon mirror. The plurality of light sources emit laser lights. The plurality of photodetectors detect beams formed by the laser lights. The plurality of optical element groups guide the beams to the photodetectors. The polygon mirror deflects the beams for scanning in one direction of the main scanning direction from one end to the other end on the opposite side of the one end. The plurality of optical element groups cross a crossing axis parallel to the main scanning direction, cross a rotation axis of the polygon mirror, and are rotationally symmetrical with respect to an axis of symmetry parallel to the rotation axis of the polygon mirror.

An optical scanning device deflects light for scanning in a main scanning direction and includes a plurality of light sources, a plurality of photodetectors, a plurality of optical element groups, and a polygon mirror. The plurality of light sources emit laser lights. The plurality of photodetectors detect beams formed by the laser lights. The plurality of optical element groups guide the beams to the photodetectors. The polygon mirror deflects the beams for scanning in one direction of the main scanning direction from one end to the other end on the opposite side of the one end. The plurality of optical element groups cross a crossing axis parallel to the main scanning direction, cross a rotation axis of the polygon mirror, and are rotationally symmetrical with respect to an axis of symmetry parallel to the rotation axis of the polygon mirror.

An image reading device includes a reading unit, a background member, and processing circuitry. The reading unit includes alight source to emit light to a passage area through which an object passes and an imaging device to capture reflected light of the light emitted to generate a visible image and an invisible image. The background member is disposed opposite the light source across the passage area. The processing circuitry is configured to: detect a change in an image characteristic due to a change in an optical characteristic of the reading unit, in invisible images obtained by capturing of invisible marks on the background member; determine a correction amount of an image characteristic to be used for correcting an image of the object generated by the imaging device, based on the change in the image characteristic detected; and correct the image characteristic based on the correction amount determined.

An image reading apparatus includes a transparent member, reading portion, a pattern, and a processor. The processor extracts a frequency component in an image of the pattern read by the reading portion in a period in which the reading portion reads an image of an original placed on the transparent member while moving in a first direction. The processor calculates a frequency component from the extracted frequency component in another position different from the position, in which the pattern is provided, with respect to the second direction crossing the first direction. The processor converts the calculated frequency component in the above-described another position into a time-series component. The processor corrects an image corresponding to the above-described another position by using the converted time-series component in the above-described another position.

An image reading apparatus includes a transparent member, reading portion, a pattern, and a processor. The processor extracts a frequency component in an image of the pattern read by the reading portion in a period in which the reading portion reads an image of an original placed on the transparent member while moving in a first direction. The processor calculates a frequency component from the extracted frequency component in another position different from the position, in which the pattern is provided, with respect to the second direction crossing the first direction. The processor converts the calculated frequency component in the above-described another position into a time-series component. The processor corrects an image corresponding to the above-described another position by using the converted time-series component in the above-described another position.

A print data editing device is configured to perform: editing print data such that when dots constituting an input image represented by the print data are compared by units of columns before and after the editing, a coincidence is maximized when an image of each column in the input image after the editing is the same position as an image of the corresponding column in the input image before the editing or is shifted by a corresponding shift amount in a sub-scanning direction relative to the image of the corresponding column in the input image before the editing. An absolute value of at least one of shift amounts for columns in the input image after the editing is one dot or greater. An absolute difference value for any two neighboring columns in a main scanning direction in the input image after the editing is one dot or less.