| 摘要 |
A scanning time is divided by the number of sides of a polygon mirror to obtain a value N. Then, it is determined whether an error has occurred. When no error has occurred, the value N is stored in an NVRAM, and a magnification correction value is calculated. Values M and N of a PLL are set based on the correction value. A difference between a clock set by the PLL and an ideal pixel clock frequency is corrected to an optimal magnification by changing a phase. The ideal pixel clock frequency after magnification correction is calculated from V=N0/NxF. The values M and N of the PLL that provide a frequency closest to the ideal frequency V are acquired. A difference between a frequency V' acquired from the values M and N and the ideal pixel clock frequency V is corrected by the clock phase.
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