PURPOSE: To obtain a highly accurate digital image even when the white level of an image signal is not flat by executing A/D conversion by using a peak value as a reference, averaging the white level of the converted digital signal to convert the digital signal into an analog signal and executing A/D conversion by using the analog signal as a reference signal.
CONSTITUTION: An output from a photoelectric conversion element 44 is detected as a peak value by a peak value detector 12 through an amplifier 11 and the peak value is converted into a digital signal through an A/D converter 13. The digital signal is sent to a comparator 14 and an averaging circuit 15 and a white level is found out and stored in a memory 16. The while level in the memory 16 is read out simultaneously with its storage and converted into an analog value through a D/A converter 17. On the other hand, an input image signal outputted from the amplifier 11 is A/D converted by an A/D converter 18 by using said analog voltage value of the white level as a reference value and outputted as a many-valued digital signal. Even when the white level of an image signal is not flat, a highly accurate digital image signal can be obtained.
KOBAYASHI YOSHIKAZU
TERAI MICHIO
HORII SHIGERU
