Image reader

摘要

There is provided an improved image reader. In the image reader, light from an object is converted into an analog signal by a photoelectric converter. The signal is quantized by an A/D converter on the basis of top and bottom reference voltages to produce a digital picture signal. A digital picture signal corresponding to a dark current flowing to the photoelectric converter is stored in a memory as a dark current data. Also a digital picture signal corresponding to the optical strength of predetermined level is stored in another memory as a white level data. Then, the top and bottom reference voltages are produced which correspond to the top and bottom quantization-threshold values on the basis of the dark current and white level data, respectively. The top and bottom reference voltages are then respectively applied to the A/D converter to produce the digital picture signal without signal distortion.