JPS60123844A - Moire inspecting device for plate making - Google Patents

Abstract

PURPOSE:To calculate a screening condition on which there is no moire by predicting whether moire is formed or not between an original and a screening screen in a screening process of plate printing. CONSTITUTION:The projection magnification of an optical system 5 in moire inspection is equalized to that in plate making. A light source 1 is turned on to project an image of an original 4 upon a screen 6 by a moire simulator 7. A periodic density variation part on the original 4 causes interference by the simulator 7 to form moire. The simulator 7 has a detection pattern in corresponding colors of a color plate, so the color of the moire is inspected to know which contact screen causes the moire; when the moire appears, the simulator 7 is rotated in a plane perpendicular to the optical axis 8 to know its angle. The inclination of a process camera to the original is varied according to said angle.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention predicts the presence or absence of a moiré phenomenon that occurs between a document used for shading and a screen used for shading in the shading process in the field of plate making printing, and The shaded area in which no moire phenomenon occurs relates to a moire inspection device for plate making whose purpose is to meet conditions.

[Prior art]

The technique of converting the shading of an original image into the size of the halftone dot area and reproducing it as a printed image is widely practiced in the fields of plate making and printing, where halftone printing using a contact screen or dot generator scanner is a process.

Since the contact screen has regularly arranged shading, if there is a part of the original image with regularly arranged shading, such as a pattern on clothing, these parts may optically interfere with each other. , shading patterns that are not present in the original often occur. This shading pattern is called moiré, and it significantly impairs image quality. Especially in the case of color printing, overprinting is performed using 4 (I!it) halftone plates for yellow ink, magenta ink, cyan ink, and black ink, which increases the chances of moiré occurring. In addition, in the case of color printing, moiré occurs between each color plate, so contact screens with different screen angles (angles formed by halftone dots extending in the vertical direction and halftone dots extending in the horizontal direction) for each color are used. is used.

Various combinations of screen angles are used in practice, but the contact screens used for prepress cameras include 0 degrees for yellow plates, 15 degrees for magenta plates, and 15 degrees for magenta plates.
The cyan version is often 75 degrees, and the bra and 7-color versions are often 45 degrees. In addition, in a color scanner, for example, MagnaScan 520 (manufactured by Crossfield), the yellow plate is 90 degrees.

The magenta version has an angle of 45 degrees, the cyan version has an angle of 75 degrees, and the black version has an angle of 15 degrees.

Conventionally, halftone photographs obtained by halftone separation were checked to see if moiré had occurred (,-). If moiré occurs in the halftone photograph, the halftone photograph is created again after shifting the arrangement angle of the contact screen or shifting the arrangement angle of the document. Therefore, this measure against moiré involves a lot of time and material loss. In particular, in color printing, if the placement angle of the contact screen is shifted, moiré may occur on the a■ of the two different contact screens, and if the placement angle of the document is shifted, , new moiré occurs between the contact screen of another color and the original, so it is impossible to eliminate the moiré with a single correction, and multiple mesh separations are required, which is extremely troublesome. Ta.

In order to deal with such a troublesome moire problem, the present inventor has proposed a moire simulator that can check whether moire will occur before performing network decomposition (Japanese Patent Application No. 165702/1982). ). This moire simulator has a moire detection pattern recorded on a sheet according to a contact screen used for plate making, and an angular scale is provided on the outer periphery of the sheet. A moire simulator for color originals uses moire detection patterns for each color that are recorded on sheets of each color while maintaining appropriate transmittance, or multiple moire detection patterns on one sheet. Duplicate records are used. By superimposing this moiré simulator on [fA],
Rotate a sheet with an edge where moire occurs, and read from the angle scale the angle at which moire does not occur or can be ignored even if it occurs. If the moire cannot be eliminated by rotating the sheet, a spacer with a known thickness is interposed between the document and the sheet to find a place where the moire can be reduced. In a moire simulator for color originals, the moire detection patterns are distinguished by color, so it is possible to know which color contact screen causes moire. By tilting and arranging the document according to the angle thus determined, or by shifting the focus according to the thickness of the spacer, it is possible to prevent moiré from occurring in the halftone photograph.

Although the above-mentioned moire simulator is extremely effective for moire inspection, there are still points to be improved as described below. Generally, when performing halftone separation, the document is enlarged or reduced, but when the magnification is changed in this way, the degree of moire may change accordingly. Since only moire can be examined, the moire that occurs when the magnification is other than the original size can only be predicted from the moire at the original size. Furthermore, although spacers are used to check for shifts in focus that eliminate moiré, it is not possible to directly determine how this corresponds to shifts in focus caused by a plate-making camera or scanner.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a moire inspection device for plate making that can check whether moire occurs or not under the same image magnification as that used during plate making.

Another object of the present invention is to provide a moire inspection device for plate making that is capable of examining deterioration in image quality caused by shifting the focus in order to eliminate moire.

[Structure of the invention]

In order to achieve the above-mentioned objects and other objects, the present invention includes a rotatable moire simulator on which a moire detection pattern is recorded, which is arranged in front of or behind a projection screen,
An optical system placed between the transparent original and the moire simulator magnifies the original to a desired magnification and projects it onto the projection screen. It is designed so that it can be moved.

FIG. 1 is an optical path diagram showing an outline of the present invention. The light emitted from the light source 1 is focused by two condenser lenses 2.3, and then reaches a transparent original (hereinafter simply referred to as an original) 4 such as a positive film, and is illuminated from behind the original 4. do. The image recorded on the original document 4 is enlarged, reduced, or at the same magnification and formed on a projection screen (hereinafter simply referred to as a screen) 6 by an optical system 5 with variable magnification.

A moire simulator 7 is placed behind or just in front of this screen 6. This moiré simulator 7 is
It is rotatable in a plane perpendicular to the optical axis 8 and movable along the optical axis 8.

In addition, in the case of the same size, the original 4 and the moiré simulator 7
The position of may be reversed. Further, the moire simulator 7 may be placed in front of or behind the document 4. In this case, the moire simulator 7 is enlarged and projected onto the screen 6 together with the original 4 by the optical system 5, so that the number of screen lines can be substantially changed. For example, a moiré simulator 7 with a screen line count of 200
If it is enlarged twice, the number of screen lines becomes 100, which has the advantage that it can be used as a substitute for a moiré simulator that has 100 screen lines.

The moire simulator 7 has a moire detection pattern recorded on a transparent plate. For example, in the case of a moiré simulator for color originals, the one shown in FIG. 2 is used. The moiré simulator 7 has a yellow sheet 20. Magenta sheet 21. Cyan sheet 2
2. Black sheet 23. Base 2 with angle scale
It consists of 4. Each of the sheets 20 to 23 has a moiré detection pattern recorded on the film in the same color as the color plate, for example yellow in the case of the yellow sheet 20, and with an appropriate light transmittance. For example, it is attached to a base 24 made of an acrylic plate in the same direction as the contact screen used during plate making. Since the moire detection pattern is preferably the same as the contact screen used for printing, a moire simulator suitable for the contact screen actually used is selected and used. In the case of a black and white moire simulator, it is recommended to use one on which the same moire detection pattern as a contact screen with a screen angle of 45 degrees is recorded on one of the bases.

In general, contact screens are specified by: the shape of the moiré detection pattern, the number of screen lines per inch, and the screen angle. The shape of this moiré detection pattern includes a cross line, square, chain, dot, ellipse, trundle angle, etc. In addition, the number of screen lines practically ranges from 60 to 200, and the higher the number of lines, the higher the ability to express between floors. For newspapers, the number is 60-65, for general books it is 85-100, and for art printing it is 133.
~175 are often used. Note that in a contact screen, the number of halftone dots is the number of screen lines. The screen angle refers to the angle formed by halftone dots extending in the vertical direction and halftone dots extending in the horizontal direction, and is determined by the specifications of the plate-making camera or scanner used.

In the moire simulator shown in Figure 2, sheets for each color plate are stacked, but four moire detection patterns are recorded in duplicate on one transparent plate, such as an acrylic plate, in the same color as the color plate. can also be used. The method of making a moire simulator in which four types of moire detection patterns are recorded on one board is described in the above-mentioned patent application No. 58-16570.
Details are given in issue 2.

When inspecting for moire, first the projection magnification of the optical system 5 is adjusted to the same value as during plate making. Next, when the light tA1 is turned on, the image of the original 4 is projected onto the screen 6 through the moire simulator.

If there is a part in the document 4 where the density changes periodically, optical interference will occur with the moiré simulator 7, and the same moiré as that which occurs during mesh separation will occur. This moire simulator 7 records each moire detection pattern in a color that corresponds to the color plate, so by examining the color of moire, it is possible to know with which contact screen moire will occur. . If this moire is occurring, the moire simulator 7 is rotated in a plane perpendicular to the optical axis 8. When the moire simulator 7 is rotated, the moire detection pattern recorded thereon and the angle scale are rotated. Then, find a place where the moiré disappears or can be ignored, and check the rotation angle at that time.

If the moire does not disappear even after rotating the moire simulator 7, move the moire simulator 7 to the angle where the moire is reduced the most, and in this state move either or both of the moire simulator 7 and the screen 6 to the optical axis 8. Shift along the line little by little. While shifting this focus, find a place where the moiré disappears or can be ignored, and check the amount of focus shift at that time. When shifting this focus, you can also see the blurring of the image of document 4, which reduces moiré and ii!
(ii) The amount of focus shift is determined by comparing and considering the deterioration in quality.

The elongation of the document 4 placed on the document table of the plate-making camera is changed according to the angle obtained as described above. For example, if the angle determined by the plate-making moiré inspection device is 15 degrees, the document 4 is rotated 15 degrees from its normal position and set on the document table. In the case of a scanner, the document is mounted on the document drum at a predetermined angle from its normal position. This also applies to scanners that do not use a contact screen and process the shading electrically. In the case of black and white originals, instead of tilting the original, you may roll the contact screen.Also, if the moiré disappears by adjusting the focus, shift the focus of the prepress camera or scanner by the amount of rubbing. .

[Configuration of Example]

FIG. 3 shows the appearance of a moiré inspection device for plate making embodying the present invention, and FIG. 4 is a sectional view thereof. A light source 31 such as a halogen lamp is provided below the casing 30, and a mirror 32 is placed behind it.
Reflects the light emitted to the rear of 1 to the front. Two condenser lenses 33 and 34 are sequentially arranged in front of the light source 31 to condense the light emitted from the light source 31 and send it to the mirror 36. This mirror 36 is attached at an angle of 45 degrees, and bends the optical axis 37 by 90 degrees in one direction. Above the mirror 36 is a Fresnel lens 38.
Further, a document table 39 made of a white acrylic plate is fitted into the opening 30a. A reference vertical line 3'9a is recorded approximately at the center of this document table 39. Note that the document table 39 may be made by layering transparent glass on the white acrylic plate, and furthermore, this document table 39 may be
In order to hold down the original 40 placed on the top of the
A document holder made of a transparent acrylic plate may also be used.

In this case, a base dollar vertical line is recorded in black on the document holding plate.

A projection lens 42 is disposed above the document table 39, and in order to prevent light from the document table 39 from entering the casing 30 through the opening 30b, the projection lens 42 is arranged above the document table 39.
A bellows 43 is attached between the projection lens 42 and the projection lens 42 . A lens barrel 44 holding the projection lens 42 is fixed to a slide lever 45 provided with a rack gear 45a. A pinion gear 47 that is rotated by a magnification adjustment knob 46 is engaged with this rack gear 45a, and by not turning the magnification adjustment knob 46, the slide lever 4
5 along the optical axis 37, the magnification of the document 40 can be set to a desired value. Note that as this magnification conversion mechanism, one used in a known projector can be used as is.

The light passing through the projection lens 42 is reflected by a mirror 50 and then enters a moire simulator 52 rotatably held by a holder 51. This holder 51 has
A screen 53 is fixed adjacent to the moire simulator 52. The rack gear 51 is attached to the holder 51.
A is formed, and a pinion gear 55 rotated by a focus adjustment knob 54 meshes with the pinion gear 55. Since a portion of the moire simulator 52 protrudes outside through the window 30C, the moire simulator 52 can be rotated with respect to the original 40 by rotating the moire simulator 52 with a finger. Also, when the focus adjustment knob 54 is rotated, the holder 5 can be moved while holding the moiré simulator 52 and the screen 53.
1 moves in the direction of the arrow, making it possible to blur the image of the original 40. When adjusting this focus, turn the focus adjustment knob 5.
4 is provided with a scale indicating the amount of deviation from the focus plane, so by reading the scale that matches the index 56, the amount of deviation from the focus plane can be determined.

An opening/closing lid 59 is attached to the upper part of the casing 30 via a hinge 5B, and the moiré simulator 52 is replaced by a power switch of the light source 31 depending on the contact screen used in the plate-making camera or scanner. Further, a changeover switch 61 switches the illuminance of the light source 31 into three levels depending on the transmission density of the original 40.

[Effect of the embodiment]

First, the power switch 60 is turned on and the light source 31 is turned on. Next, the original 40 is placed on the original table 39, and the magnification joint knob 46 is turned to set the same magnification as that used during plate making. When this magnification adjustment knob 46 is turned, the pinion gear 47 rotates, and the slide lever 45 moves up and down, moving the projection lens 42 along the optical axis 37.
Set it to the desired magnification position. Further, the focus adjustment knob 54 is adjusted so that the screen 53 is aligned with the focal plane of the projection lens 42.

The original II% 40 placed on the document table 39 is illuminated with illumination light from the light source 31. This original 40 is projected onto a screen 53 by a projection lens 42 set at a desired magnification. Here, since the image of the original 40 is projected onto the screen 53 after passing through the moiré simulator 52,
If there is a portion in the document 40 where the density changes periodically, optical interference will occur with the moiré simulator 52, resulting in the same moiré that occurs during screen separation. If this moire is occurring, the moire simulator 52, a portion of which is exposed through the window 30c, is rotated. When the moire simulator 52 is rotated, the moire detection pattern recorded thereon and the angle scale are rotated.

Then, find a place where the moire disappears or can be ignored,
The angle scale that coincides with the image 39a° of the reference vertical line 39a at that time is examined.

If the moire simulator 52 does not disappear even after rotating the moire simulator 52, move the moire simulator 52 to the angle where the moire is reduced the most, and in this state turn the focus adjustment knob 54.
holder 51 from the focal plane of the projection lens 42.
, and move the moire simulator 52 and screen 53 little by little. While shifting this focus,
Find a place where the moiré disappears or can be ignored, and read the amount of focus shift at that time from the scale on the focus adjustment knob 54. When shifting the focus, the amount of focus shift is determined by comparing the reduction in blur and the deterioration in image quality.

〔Effect of the invention〕

The present invention having the above configuration uses an optical system that can be adjusted to a desired magnification and projects the image of the original onto a screen through a mower and a resimulator, so moiré occurs under the same conditions as during plate making. It is possible to investigate the age of people and their trends. In addition, when removing moire by shifting the focus, you can know the degree of blurring of the image at the same time as the moire fades and fades, so you can weigh the improvement in image quality due to eliminating moire and the deterioration in image quality due to blur. It is possible to check the out-of-focus point (■) that gives the best image quality. Furthermore, since a spacer is not used as in the conventional case, the focus can be shifted steplessly.

[Brief explanation of drawings]

FIG. 1 is an optical path diagram showing an outline of the present invention. FIG. 2 is an exploded perspective view showing an example of a moiré simulator. FIG. 3 is an external view showing an example of a moire inspection device for plate making in which the present invention is implemented. FIG. 4 is a sectional view of FIG. 3. l...Light source 4...Original 5...Optical system 6...Screen 7...Moiré simulator. 31... Light source 38... Fresnel lens 396. Original table 39a...Reference vertical line. 40... Original 42... Projection lens 46... Magnification adjustment knob 52... Moiré simulator 53... Screen 54... Focus adjustment knob.

Claims (4)

[Claims] (1) A variable magnification optical system that forms a real image of a transparent original onto a projection screen, and a light source that illuminates the original. A moire simulator on which a moire detection pattern is recorded is arranged so as to be rotatable within a plane perpendicular to the optical axis of the optical system, and the screen and/or the moire simulator is placed on the optical axis of the optical system. 1. A moiré inspection device for plate making, comprising a moving means. (2) The moiré simulator is a contact screen for yellow used during plate making, a contact screen for magenta [
2. The moire inspection device for plate making according to claim 1, wherein four types of moire detection patterns are recorded in respective colors according to the screen, the contact screen for cyan, and the contact screen for blank. (3) The four types of moire detection patterns are recorded on four sheets, and the moire simulator is constructed by overlapping them. Moiré inspection device for plate making. (4) The moire inspection device for plate making according to claim 2, wherein the four types of moire detection patterns are recorded overlappingly on one transparent plate.