US 5,132,723 A · Method and apparatus for exposure control in light valves

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.

Claims19

Dependent claims

In a light imaging assembly which includes a light valve having rows and columns of modulating cells, circuitry for shifting data from one row to the next, a light source, two-dimensional imaging surface and associated control circuitry for shifting the date from row to row at a rate so as to produce a stationary image relative to the imaging surface, a method of image projection, comprising:

(a) transferring the digital data to be imaged to a first row of modulating cells of said light valve and then to subsequent rows;
(b) imaging light onto said light valve in a direction such that each cell, when activated by said data, redirects incident light onto the imaging surface;
(c) moving the imaging surface relative to incident image light from said light valve so that the image is substantially stationary relative to the imaging surface;
and
(d) selectively inhibiting cells in columns of said light valve from turning on so that each column produces a desired exposure level on said imaging surface when modulated by image data.

2 more elements

Apparatus for imaging data onto an imaging surface, comprising:

(a) a two-dimensional light valve made up of a plurality of rows and columns of light modulating cells;
(b) a light source positioned so as to illuminate said light valve;
(c) an imaging surface positioned so as to intercept light from said light valve;
(d) a lens assembly for focusing light from said light source onto the valve and for directing the light coming from the valve onto the imaging surface;
(e) associated control circuitry coupled to said light valve operative in response to control signals to control activation of said cells;
(f) means for generating relative motion between the imaging surface and the imaging light from the light valve;
(g) means for inputting data to be imaged to the first row and then shifting it to subsequent rows of the light valve at a rate such that the image of the data pattern relative to the imaging surface is stationary;
and
(h) means for inhibiting a selected number of cells in each of said columns of cells such that the exposure on said imaging surface from each of said columns in the absence of imaging data is substantially the same.

6 more elements

Dependencies are inferred from the claim text.

Method and apparatus for exposure control in light valves

Life of this patent

Method and apparatus for exposure control in light valves

Life of this patent

Abstract

Claims19