METHOD FOR CORRECTING SHADING AND SCANNER DEVICE

摘要

A shading correction of removing a plurality of shading factors is performed. A scanner device performs a shading correction in a manner such that a low-pass filter circuit (14) extracts a broad waveform change component caused by a temperature characteristic and a temporal change in light source or sensor sensitivity as shading factors, a phase/amplitude synchronizing circuit (15) extracts a phase shift of a cycle pattern of a lens array, a first multiplying circuit (16) synthesizes the waveforms of the extracted factors so as to form a correction-purpose image signal waveform, and the correction-purpose image signal waveform is divided from an image signal waveform subjected to a dark level correction (offset).

主权项

1. A scanner device that optically scans an image recorded on an original by an image sensor, comprising:
an image sensor that reads an image of an original and a white reference inside the scanner device; a production-time white level waveform memory that stores a production-time white level waveform read by the image sensor when the scanner device is produced; an analog circuit and A/D converter that converts a digital image signal read by the image sensor into a digital image signal; a dark level waveform memory that stores a dark level waveform read by the image sensor in a non-illumination state; a dark level correcting circuit that performs a dark level correction by subtracting the dark level waveform from an image signal waveform output from the analog circuit and A/D converter by the use of the dark level waveform stored in the dark level waveform memory; a first dividing circuit that performs a white level correction of dividing the production-time white level waveform stored in the production-time white level waveform memory from an image signal waveform subjected to a dark correction and output from the dark level correcting circuit; a low-pass filter circuit that outputs an image signal waveform of a broad change component caused by a temporal change in light source or sensor sensitivity and a temperature characteristic by outputting only a low-frequency component of the image signal waveform output from the first dividing circuit; a phase/amplitude synchronizing circuit that outputs a cycle pattern caused by a phase shift of a lens cycle pattern separated from a low-frequency component or a noise component by synchronizing the phase and the amplitude of the image signal waveform output from the low-pass filter circuit based on the input of the white level correction image signal waveform output from the first dividing circuit; a first multiplying circuit that outputs a result obtained by multiplying the cycle pattern of the phase shift output from the phase/amplitude synchronizing circuit with the image signal waveform of the broad change component output from the low-pass filter circuit; a second multiplying circuit that outputs a correction white level waveform obtained by multiplying the production-time white reference level waveform stored in the production-time white level waveform memory from the image signal waveform obtained by multiplying the cycle pattern of the phase shift and the image signal waveform of the broad change component by the first multiplying circuit; a correction white level waveform memory that stores the correction white level waveform output from the second multiplying circuit; and a dividing circuit that outputs a result obtained by dividing the correction white level waveform output by the correction white level waveform memory from the dark correction image signal waveform output by the dark level correcting circuit.