| 摘要 |
PURPOSE:To prevent a decrease in detection precision even if dust sticks to a light emitting element, by controlling the balance of hue between and the light and shade of two light emitting elements. CONSTITUTION:When a light emitting diode 12 decreases in light output,a driving circuit 312 performs control by a sample-held hue signal so that light emitting diodes 12 and 13 have the same light outputs. Similarly, when the light emitting diode 13 decreases in light output, a driving circuit 322 performs control in the same way. Then, when printed matter is inserted between the light emitting diodes 12 and 13, and photodiodes 141 and 142 and then conveyed, sample holding circuits 311 and 321 output hue signal right before a gate signal is ceased to sample holding circuits 312 and 322. Namely, feedback control is not performed on the basis of the hus signals detected while the printed matter is passed. |
