Importance

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Abstract

A system for automatically re-calibrating a spectrophotometer which is mounted at one side of the printed sheets output path of a color printer for measuring the colors printed on colored test patches on printed test sheets moving thereby as the test patches are sequentially illuminated with multiple different color illumination sources, which illumination colors are reflected from the test patches and detected by a photosensor providing electrical output signals. Re-calibration is provided by illuminating, with the same sequenced illumination sources, during a time coinciding with an adjacent gap between the printed sheets moving in the output path, a stationary calibration test patch which is mounted on the opposite side of the output path from the spectrophotometer, to provide respective calibration signals from respective electrical output signals of the photosensor during a time interval when a printed color sheet is not in said output path in between the spectrophotometer and the calibration test patch. This re-calibration timing may be provided by the existing sheets positions tracking control system of the printer. The calibration test patch may be a standard white tile test surface, and may be mounted slightly outside of the output path to avoid contamination.

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First Claim