Importance

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Abstract

A method and apparatus for exposure control of images formed by two dimensional light valves allows precise exposure control, high degree of exposure uniformity and immunity from defects in the light valve. The light valve is being imaged onto an object, for example a sheet of light sensitive material, and the image is scanned along the object either by moving the object or the image. The data to be imaged is entered into the first row of the light valve and as the image of the light valve is scanned along the object, the data in the first row is transferred to subsequent rows at a direction and rate that keeps the imaged data stationary relative to the object. By using a large number of rows the exposure of each image point on the object is the sum of many exposures, each exposure contributed by one row. The number of rows each bit of data travels is electronically controlled in order to determine the exposure generated by the data bit. To calibrate the device for a uniform exposure on the object the total exposure generated by each column is measured and the length of the column (i.e. the number of rows it contains) is electronically set to achieve equal exposure from all columns. Illumination non-uniformity across the light valve as well as defective cells are automatically compensated for by this method.

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First Claim