IMAGE EXPOSURE SYSTEM
BACKGROUND OF THE INVENTION
This invention relates to an image exposure system comprising an exposure unit which converts image data into a light signal defining specific exposure levels for individual pixels and outputs the light signal onto photographic printing paper.
Image exposure systems which can read image data recorded on a photographic film or a similar recording medium, translate it into a light signal and expose photographic printing paper with the light signal are commonly used in recent years. An exposure unit of this type of image exposure system for exposing the photographic printing paper includes a light source and an exposure head for projecting light emitted from the light source in accordance with the image data onto the photographic printing paper along its widthwise direction.
The exposure head typically comprises a shutter array composed essentially of a lead lanthanum zirconate titanate (PLZT) device. The PLZT device includes a plurality of shutter elements aligned in a linear array that are formed from a translucent ferroelectric ceramic material obtained by adding lanthanum to lead zirconate titanate (PZT). Operation of this shutter array (hereinafter referred to as the PLZT shutter array) is as follows. When a driving voltage is applied to a shutter element located at a position corresponding to a particular pixel of the original image data, the shutter element opens, allowing the light from the light source to pass through the shutter element and fall on the photographic printing paper to expose it.
One problem encountered with the image exposure system thus constructed is that output characteristics of the exposure unit can vary due to changes in light transmitting characteristics of the shutter elements with the lapse of time, causing differences in the intensity of light passing through the individual shutter elements. This can result in large variations in exposure levels achieved with the individual shutter elements and eventual degradation in the fidelity of image reproduction. A conventional approach taken in coping with this problem is to install an optical sensor beneath the PLZT shutter array for measuring the intensity of light transmitted through the individual shutter elements and alter their output light intensities to cancel out or minimize, the differences in exposure levels among the individual shutter elements in accordance with correction data obtained from output signals of the optical sensor.
The aforementioned image exposure system employing the built-in optical sensor is however associated with another problem that dimensions of the exposure unit become too large. This is because the PLZT shutter array is required to completely cover the width of the photographic printing paper which is advanced in a particular direction to enable exposure all across the photographic printing paper, and the optical sensor for measuring the intensity of light transmitted through the individual shutter elements should cover the whole shutter elements.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image exposure system which overcomes the problems residing in the prior art
It is another object of the present invention to provide an image exposure system which allows automatic exposure level correction of individual light output elements of an
exposure unit to minimize differences in exposure levels among the individual light output elements without causing an increase in physical dimensions of the exposure unit According to the present invention, an image exposure
5 system comprises an exposure unit having a plurality of light output elements for converting image data into a light signal which causes a specific level of exposure of each pixel and outputting the light signal onto photographic printing paper to expose it, a measuring device for measuring the density
10 of each pixel of an image produced by exposing the photographic printing paper with reference image data at the exposure unit, and a compensator for correcting exposure levels achieved with the individual light output elements based on measurement results obtained by the measuring
15 device to reduce differences in the exposure levels among the individual light output elements caused by changes in output characteristics of the exposure unit.
The image exposure system thus constructed makes it possible to automatically correct the exposure levels
20 achieved with the individual light output elements to reduce the differences in the exposure levels based on pixel density data obtained by the measuring device. Also, this eliminates an optical sensor, and can thus assure a compact size for the exposure unit.
These and other objects, features and advantages of the invention will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings.
30 BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram generally showing a configuration of an automatic photograph printing system employing an image exposure system according the invention; 35 FIG. 2 is a diagrammatic representation of a reference image data stored in the automatic photograph printing system of FIG. 1;
FIG. 3 is a diagram showing a construction of a second exposure unit of the automatic photograph printing system 40 of FIG. 1;
FIGS. 4A and 4B are a plan view and a cross-sectional side view of a PLZT shutter array of the second exposure unit shown in FIG. 3, respectively; 45 FIG. 5 is a perspective diagram showing a construction of a scanner of the automatic photograph printing system of FIG. 1;
FIG. 6 is a diagram showing a construction of a slit plate provided in the scanner of the automatic photograph printing 50 system of FIG. 1; and
FIG. 7 is a diagram showing an alternative configuration of the second exposure unit of the automatic photograph printing system.
DETAILED DESCRIPTION OF THE
FIG. 1 is a block diagram generally showing the configuration of an automatic photograph printing system employing an image exposure system according to a preferred
60 embodiment of the invention. As shown in the FIG. 1, the automatic photograph printing system comprises a first exposure processor 10 for exposing photographic printing paper 13 by projecting images recorded on an negative film 11 upon the photographic printing paper 13, an image
65 information storing unit 20 for storing image data entered from an external system such as a personal computer, a second exposure processor 30 for exposing the photographic