A rotating polygonal mirror has deflection faces for deflecting a light beam. A motor drives the polygonal mirror. A first detection unit outputs a first signal by detecting a light beam. A second detection unit outputs a second signal whose period is different from a period of the first signal, by detecting magnetic flux change. A specifying unit obtains a phase relationship between the first signal and the second signal, and specifies a deflection face. A storage unit stores setting information for setting whether to use rising or falling of the second signal to specify the phase relationship. The specifying unit determines whether to use rising or falling of the second signal in order to obtain the phase relationship.

A light-source-driving control device thins a pixel at an edge portion of image data by a first pixel width; sets a second pixel width at the edge portion such that a ratio between the first and second pixel widths is constant; creates light amount information including a first light amount with which a pixel not included in the set second pixel width is exposed, and a second light amount with which a pixel included in the second pixel width is exposed; selects the first or second light amount based on a power-modulation control signal; drives light sources according to the selected light amount and a light-source-modulation pulse signal; and counts an addition value of pixel density considering a pixel width and a light amount, based on a data-width setting signal based on the second pixel width, and on a light-amount setting signal based on the light amount information.

In image-checking equipment, a detector reads a line-shaped check image formed on a sheet and acquires image data on the check image. A controller calculates an edge blur in a rising edge and a falling edge of the image data, calculates a line width of the check image. The controller refers to a correction table with the measured values of the edge blur and the line width of the check image, and acquires a corrected line width value based on the correction table to obtain the real line width of the check image.

An image forming apparatus includes a reading unit for sequentially reading, from image data, pieces of pixel data of target pixels along a predetermined direction, a cumulative sum calculation unit for calculating a cumulative sum of gradation values represented by pieces of pixel data of target pixels in a significant image portion read by the reading unit, a determination unit for determining whether the target pixel read by the reading unit is located at a boundary between the significant image portion and a background portion that is a non-significant image portion, and a correction unit for correcting, if the determination unit determines that the target pixel is located at the boundary, a gradation value represented by pixel data of the target pixel by adding a correction amount based on the cumulative sum up to the target pixel calculated by the cumulative sum calculation unit to the gradation value.

In a case where a line width defined by a drawing command that is given to draw the line is smaller than a predetermined width, a line width of the drawing command is changed to a predetermined even-number pixel width.

A light-source-driving control device thins a pixel at an edge portion of image data by a first pixel width; sets a second pixel width at the edge portion such that a ratio between the first and second pixel widths is constant; creates light amount information including a first light amount with which a pixel not included in the set second pixel width is exposed, and a second light amount with which a pixel included in the second pixel width is exposed; selects the first or second light amount based on a power-modulation control signal; drives light sources according to the selected light amount and a light-source-modulation pulse signal; and counts an addition value of pixel density considering a pixel width and a light amount, based on a data-width setting signal based on the second pixel width, and on a light-amount setting signal based on the light amount information.