Image data reading apparatus

Claim 1

An image data reading apparatus comprising: transport means for transporting a document along a transport path within the image data reading apparatus, the document carrying image information on a front surface thereof; a white reference plate provided at a first position in the transport path to confront an opposite side of the front surface of the document; a light source for generating a light being projected to the first position through which the document is transported along the transport path; light receiving means for photoelectricically converting a light reflected from the white reference plate into a white reference signal and for photoelectrically converting a light reflected from the document into an image signal; correction means for eliminating a shading from the image signal supplied by the light receiving means based on the white reference signal which is supplied by the light receiving means before the document is transported to the first position; peak level holding means for detecting and storing a peak level of the image signal supplied from the light receiving means to the peak level holding means through the correction means; quantization means for converting a signal supplied from the light receiving means into digital information based on the peak level of the image signal stored by the peak level holding means, the peak level of the image signal being used as a reference voltage for the quantization means to convert the image signal into digital information; and switching means for turning the peak level holding means OFF to stop detecting and storing of the peak level of the image signal for a prescribed time period between the white reference signal is received by the light receiving means from the white reference plate and a time the document is transported to the first position along the transport path, so that the peak level holding means receives no signal from the light receiving means during said prescribed time period.