Importance

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Abstract

An image signal processor is capable of precisely reading a dark-colored character or the like drawn on a light-colored background, such as a white board, and to perform binary encoding, but also capable of precisely reading a light-colored character or the like drawn on a dark-colored background, such as a blackboard, and to perform binary encoding. The image signal processor includes an automatic gain control circuit for receiving an image signal generated by an image pickup element and for changing to either a first cutoff frequency for performing automatic gain control on only a low-frequency component of the signal or a second cutoff frequency for performing automatic gain control on both the low-frequency component and a high-frequency component of the image signal. A binary encoding circuit receives an output signal generated as a result of the automatic gain control operation in the automatic gain control circuit and compares the output signal with a threshold potential level; to generate a binary signal when the threshold potential level is lower than the potential level of a frequency component of the output signal. A separate threshold potential level and frequency component is used when the different background modes are selected. A gate circuit which is operated in conjuction with the change of the cutoff frequency is used to select the binary signal from the binary encoding circuit corresponding to the selected background mode.

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First Claim