Patent ID: 6466337
Filing Date: 2002-10-15
Classification: H04N

Abstract:
A method for calibration of an optoelectronic scanner element of a scanner device for point-by-point and line-by-line scanning of an image original, comprising the steps of:illuminating an image original and converting scan light modulated with densities of the scanned image original into image values with a light/voltage transducer unit; predetermining a white level; undertaking the calibration of the scanner element by changing a gain of the light/voltage transducer unit such that an image value generated when scanning a brightest location of the image original, a white point, corresponds to the predetermined white level; charging the light/voltage transducer unit with a calibration light; measuring transducer densities as a criterion for attenuation of the calibration light respectively simulated by different gains from measured image values U*B given different gains of the light/voltage transducer unit, and allocating identified transducer densities DH to the corresponding gains as a transducer density table; determining diaphragm densities DB as a criterion for the attenuation of the calibration light achieved with respective scan diaphragms from the image values U*B that were measured given different scan diaphragms in the calibration light, and allocating the identified diaphragm densities DB to the corresponding scan diaphragms as a diaphragm density table; determining a reference diaphragm and a corresponding reference diaphragm density DRB from the diaphragm density table; implementing a calibration with the identified reference diaphragm by setting the gain of the light/voltage transducer unit such that the image value U*B acquired with the calibration light attenuated by the reference diaphragm corresponds to the predetermined white level UW, and determining a reference transducer density DRH belonging to the gain that has been set from the transducer density table; determining the scan diaphragm for scanning the image original and the corresponding diaphragm density DB from the diaphragm density table; calculating an overall density DGS from the reference diaphragm density DRB, the reference transducer density DRH, the diaphragm density DB of the scan diaphragm and from the density DW of the white point of the image original; determining a gain of the light/voltage transducer unit that is allocated in the transducer density table to that transducer density DH that corresponds to the calculated overall density DGS and; setting the gain that has been determined at the light/voltage transducer unit for scanning the image original.