Weisspegel Detektorschaltung für einen optischen Bildabtaster.

摘要

In the white level detection circuit for an optical image reader, for a low value portion in an image, the white level signal corresponding to an image signal of a high value background portion which precedes to the low value portion is held steady. Accordingly, even if the low value image portion has a long duration, the white level signal may be kept at a proper value for the image signal corresponding to the low value image signal. For the high value background portion, the white level signal that immediately follows a variation of the image signal can be obtained. Therefore, a proper white level signal can be generated for the background portion. Various processing applied to the image signal on the basis of the white level signal may be performed in a satisfactory manner. As a consequence, the read performance of the optical image reader may be remarkably improved.