Importance

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Abstract

A plurality of electrometer probes (3, 4, 5, 6) scan charge patterns of a photoconductor (1) which is locally uniformly charged prior to the X-ray exposure and is discharged by the exposure in dependence on the intensity of the X-rays. The surface of the photoconductor is scanned after the exposure in order to determine the charge density, the electrometer probes (3, 4, 5, 6) forming for each pixel a pixel value which corresponds to the discharge at the relevant pixel to compensate for sensitivity fluctuations of the electrometer probes included is a calibration operation for the sensitivity of all electrometer probes in that two probes (3, 4, 5, 6) scan an identical section (a.sub.1 . . . d.sub.3) of the image, their relative sensitivity used for correcting the pixel values is derived from comparison of the resultant output signals of the probes (3, 4, 5, 6).

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First Claim