JP2004317545A - Method for setting amount of light in image exposure apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably improve picture quality even when the focal position is deviated. <P>SOLUTION: The method for setting the amount of light in an image exposure apparatus which scans a photosensitive material with a light beam to record an image includes the steps of: setting a first amount of light for exposure; setting a second amount of light for exposure in accordance with the changes in image signals; detecting the focal position of the light beam; changing the second amount of light in accordance with the detected focal position. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light amount setting method in an image exposure apparatus, and more particularly, to an image exposure technique that stably improves image quality by increasing an edge light amount in conjunction with a focal position shift.
[0002]
[Prior art]
In recent years, CTP (Computer to Plate), in which a computer creates a digital image and directly records an image on a printing plate without interposing a film during plate making, has been performed. As an image forming apparatus used in such a CTP or the like, an image forming apparatus that records an image by performing laser light exposure according to a digital image signal while holding a photosensitive material on the surface of a rotating drum is used. .
[0003]
In this technique, the lighting state of the light beam emitted from the exposure light source is controlled by a binarized image signal generated based on the image data of the original image to be recorded, and the exposure light source and the light-sensitive material are relative to each other. By moving the light beam two-dimensionally, the light beam is scanned two-dimensionally on the photosensitive material, and a desired image is recorded on the photosensitive material.
An image for plate making is a halftone image using so-called halftone dots, and each halftone dot is a plurality of dots formed by scanning exposure using a light beam having a predetermined size determined according to the resolution. Recorded by set.
[0004]
Conventionally, in such an exposure apparatus, when the quality of the laser beam deteriorates, an edge signal is created from the on / off signal of the laser beam, and the light quantity at that moment is changed to improve the image quality. It was.
For example, in order to increase the brightness of the light source when exposing the contour portion of the image recorded on the photosensitive material and sharpen the density edge in the contour portion, the binarized signal is differentiated to enhance the edge. A method has been proposed (see, for example, Patent Document 1).
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 08-023422
[Problems to be solved by the invention]
However, in a system in which a plate is wound around the outer peripheral surface of a drum and exposed with a light beam as disclosed in the above-mentioned patent document, there is no problem with the image improvement method at the focal position, but the focal position fluctuates when the drum rotates. For this reason, there is a problem that the image quality improvement effect is insufficient at the position where the focus is shifted.
Further, when the amount of edge light is increased as it is, there is a problem that overcorrection occurs.
[0007]
The present invention has been made in view of the above-described conventional problems, and provides a light amount setting method in an image exposure apparatus that can stably improve image quality even when the focal position is deviated. Let it be an issue.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, a first aspect of the present invention is a light amount setting method in an image exposure apparatus that records an image by scanning a light beam with respect to a light-sensitive material. A step of setting, a step of setting a second exposure light amount set in conjunction with a change in the image signal, a step of detecting a focal position of the light beam, and the step of detecting the focal position of the light beam. And a step of changing a second exposure light quantity. A light quantity setting method in an image exposure apparatus is provided.
[0009]
Similarly, in order to solve the above problem, a second aspect of the present invention is a light amount setting method in an image recording apparatus for recording an image by scanning a light beam with respect to a light-sensitive material. A step of setting a light amount; a step of setting a second exposure light amount set in conjunction with a change in the image signal; a step of detecting an exposure position of the photosensitive material; and a detected exposure position of the photosensitive material And a step of changing the second exposure light quantity using a table set in advance based on the information. A light quantity setting method in an image exposure apparatus is provided.
[0010]
The first exposure light amount is preferably set using a shading table linked to the exposure position information.
[0011]
Further, it is preferable that the first exposure light amount is used when the non-edge portion is exposed, and the second exposure light amount is used when the edge portion is exposed.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a light amount setting method in an image exposure apparatus of the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings.
[0013]
FIG. 1 is a block diagram showing a schematic configuration of a circuit for performing a light amount setting method in the image exposure apparatus according to the first embodiment of the present invention.
In FIG. 1, the image exposure apparatus according to the present embodiment records an image by scanning and exposing a plate 12 wound around the outer peripheral surface of a drum 10 with a light beam emitted from a laser diode (LD) 14. is there.
[0014]
At this time, the present embodiment is intended to improve the image quality by increasing the amount of light at the edge portion in conjunction with the focal position with respect to the quality deterioration of the light beam.
[0015]
Therefore, a plate floating sensor 16 is provided to detect the focal position, and a rotary encoder 18 is provided to detect the rotational position (main scanning direction position) of the drum 10.
The plate floating sensor 16 applies a laser beam to the surface of the plate 12, receives the reflected light, and measures the distance from the plate floating sensor 16 to the surface of the plate 12. It is to detect that it is not properly wound and is floating.
The detection signal of the plate floating sensor 16 is input to the conversion table 20, converted by the conversion table 20, and input to the edge light amount up level setting circuit 22.
[0016]
The edge light quantity up level setting circuit 22 is for setting a light quantity increase (second exposure light quantity) to be increased from a normal exposure light quantity level (first exposure light quantity) when exposing a non-edge portion. The edge light intensity up level setting circuit 22 is input with an edge detection signal (edge rising and falling) detected by the edge detection circuit 26 from the image ON / OFF signal 24. The edge light quantity up level setting circuit 22 sets an edge light quantity level (second exposure light quantity) that should be added to the normal exposure light quantity level at the edge portion by this edge detection signal.
[0017]
Further, as described above, the signal detected by the plate floating sensor 16 and converted by the conversion table 20 is input to the edge light quantity up level setting circuit 22, and the edge light quantity up level setting circuit 22 is based on this signal. The edge light quantity level is changed in conjunction with the focal position. As a result, information from the plate floating sensor 16 is fed back to the exposure light quantity.
[0018]
On the other hand, the detection signal of the rotary encoder 18 is input to the address generation circuit 28. The address generation circuit 28 generates an address on the plate 12 indicating the position in the main scanning direction from this detection signal.
The shading table 30 is a table showing the actual exposure light quantity set in advance, so that shading correction data is input to the exposure light quantity level setting circuit 32 based on the address on the plate 12 detected above. It has become.
The exposure light quantity level setting circuit 32 sets the exposure light quantity level (first exposure light quantity) in normal exposure based on this data.
[0019]
On the other hand, the edge light amount level set by the edge light amount up level setting circuit 22 is inputted to the adder 36 only at the edge portion via the ON / OFF circuit 34.
The normal exposure light level set in the exposure light level setting circuit 32 is also input to the adder 36.
Since the edge light amount level is input to the adder 36 only at the edge portion by the action of the ON / OFF circuit 34, the adder 36 adds the edge light amount to the normal exposure light amount only at the edge portion.
[0020]
In this way, the normal exposure light amount is input to the ON / OFF circuit 38 in the non-edge portion, and the exposure light amount level obtained by adding the normal exposure light amount and the edge light amount is added to the ON / OFF circuit 38 in the edge portion. Is input.
In the ON / OFF circuit 38, on / off is controlled by the image ON / OFF signal 24, and the image signal converted into the exposure light amount is output to the laser diode 14 only when the image is on. Thereby, based on the information fed back from the plate floating sensor 16, the exposure light quantity at the edge portion is increased using the edge light quantity that is changed in conjunction with the focal position.
[0021]
As described above, according to the present embodiment, stable correction is realized by feeding back the information from the plate floating sensor 16 and changing the amount of edge light in conjunction with the focal position.
[0022]
Next, a second embodiment of the present invention will be described.
FIG. 2 is a block diagram showing a schematic configuration of a circuit that performs the light amount setting method in the image exposure apparatus according to the second embodiment of the present invention.
As shown in FIG. 2, the image exposure apparatus of the second embodiment is almost the same as the image exposure apparatus of the first embodiment described above. The difference between the image exposure apparatus of the second embodiment and the image exposure apparatus of the first embodiment is that there is no plate floating sensor provided for detecting the focal position in the first embodiment.
[0023]
That is, in the second embodiment, the focal position is not actually detected, but the focal amount variation is measured in advance, and the focal position deviation is predicted and fed back using the result.
The method of feeding back the focus variation amount from the previous measurement result is not particularly limited, and examples thereof include the following method.
[0024]
One is a method of feeding back the focal position fluctuation amount due to the sub-scanning position. This is achieved by estimating the focal position based on focus position shift information generated by deformation of a rail or the like of a sub-scanning mechanism (not shown) that moves the exposure unit including the laser diode 114 along the axial direction of the drum 110, and feeds back. Based on this information, the edge light quantity is changed.
[0025]
The other is a method of predicting the amount of deformation that is deformed by the rotation of the drum 110 and feeding back focal position deviation information estimated from the amount of deformation. The deformation of the drum 110 can be estimated from the position of a chuck (not shown) that fixes the plate 112 to the drum 110, and a value estimated from an actual measurement result is fed back. That is, the amount of deformation of the drum 110 is calculated from the position of the chuck detected by the rotary encoder 118 and fed back.
At this time, the detection signal of the rotary encoder 118 is input to the conversion table 120 via the address generation circuit 128. The conversion table 120 estimates the focal position deviation amount based on data such as plate thickness, plate size, and drum deformation amount measured in advance.
[0026]
By these methods, the edge light quantity up level setting circuit 122 changes the edge light quantity up level in conjunction with the focal position based on the estimated focal position information.
Since the functions of other parts are the same as those of the first embodiment described above, in FIG. 2, the same components as those in FIG. I will do it.
[0027]
Thus, according to the present embodiment, real-time correction using the plate floating sensor 16 is not required as in the first embodiment, and the exposure light amount at the edge portion is corrected in conjunction with the rotational position of the drum 110. It becomes possible. Thereby, also in this embodiment, even if a focus position shifts, image quality is stably improved.
[0028]
According to each of the embodiments described above, since the exposure light amount increase level at the edge portion is changed in conjunction with the focal position, a stable image quality improvement effect is always obtained even if the focal position fluctuates. Can be obtained.
In addition, the image quality is improved by increasing the amount of light only at the edges, not by increasing the total amount of light, thus protecting the environment such as extending the life of the laser diode and reducing the temperature rise. Also has an effect.
[0029]
As described above, the light amount setting method in the image exposure apparatus of the present invention has been described in detail. However, the present invention is not limited to the above embodiment, and various improvements and modifications can be made without departing from the gist of the present invention. Of course, changes may be made.
[0030]
【The invention's effect】
As described above, according to the present invention, when a plate is wound around the outer peripheral surface of a drum and an image is recorded by exposure with a light beam, a stable image quality improvement effect is always obtained even if the focal position fluctuates. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a circuit for performing a light amount setting method in an image exposure apparatus according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a schematic configuration of a circuit for executing a light amount setting method in an image exposure apparatus according to a second embodiment of the present invention.
[Explanation of symbols]
10, 110 Dora 12, 112 Plate 14, 114 Laser diode 16 Plate floating sensor 18, 118 Rotary encoder 20, 120 Conversion table 22, 122 Edge light quantity up level setting circuit 24, 124 Image ON / OFF signal 26, 126 Edge detection circuit 28, 128 Address generation circuit 30, 130 Shading table 32, 132 Exposure light level setting circuit 34, 38, 134, 138 ON / OFF circuit 36, 136 Adder

Claims (4)

A light amount setting method in an image exposure apparatus that records an image by scanning a light beam with respect to a photosensitive material,
Setting a first exposure light amount;
Setting a second exposure light amount set in conjunction with a change in the image signal;
Detecting a focal position of the light beam;
Changing the second exposure light amount in conjunction with the detected focal position;
A light amount setting method in an image exposure apparatus. A light amount setting method in an image recording apparatus for recording an image by scanning a light beam with respect to a photosensitive material,
Setting a first light quantity;
Setting a second exposure light amount set in conjunction with a change in the image signal;
Detecting an exposure position of the photosensitive material;
Based on the detected exposure position information of the light-sensitive material, changing the second exposure light amount using a preset table;
A light amount setting method in an image exposure apparatus. The light quantity setting method in the image exposure apparatus according to claim 2, wherein the first exposure light quantity is set using a shading table linked to the exposure position information. The image exposure apparatus according to claim 1, wherein the first exposure light amount is used when exposing a non-edge portion, and the second exposure light amount is used when exposing an edge portion. Light quantity setting method.

Images