JPH068067B2 - Image reproduction - Google Patents

Description

The present invention relates to an image reproduction, and more particularly to an image reproduction in which an image is formed by halftone dots or lines. Conventionally, it is well known to change the size of halftone dots or the thickness of lines in order to reproduce an image having density gradation. In such an image reproduction with halftone dots or lines, the screen frequency of the halftone dots or lines is constant regardless of whether the density of the original is changed or not.

An image reproduction that represents an image with halftone dots or lines is a sheet of paper that has been facsimile-printed with an image, or a printing method such as gravure printing, letterpress printing, lithographic printing, paper, synthetic resin film, or metal. Examples include a plate, a wood plate, and other materials to be printed with an image printed thereon, or a printing plate or a color separation film that operates in a printing process or a plate-making process for printing these.

By the way, regarding the relationship between the screen ruling and the duplicate image, the greater the screen ruling, the better the reproducibility of the details of the duplicate image, but the higher the reproduction density in the halftone portion, and the tone of the duplicate image in the shadow portion. The flatness of the image and the coarser the screen ruling, the poorer the reproducibility of the details of the duplicate image, but the contrast of the shadow portion of the duplicate image is stronger and the printed matter is more powerful. Are known.

However, in the conventional image duplicate, the screen ruling of the duplicate image is constant regardless of whether or not the density of the original image is changed as described above.

Therefore, the conventional image reproduction sacrifices the reproducibility and strength of the shadow part if it has a screen frequency suitable for the light part, and it has a screen frequency suitable for the shadow part. If so, the reproducibility of the light part is sacrificed, and the reproduction from the light part to the shadow part is not reproduced under optimal conditions, but the reproducibility of any part is sacrificed.

The present invention is intended to solve the above-mentioned drawbacks of conventional image reproductions and to provide image reproductions having excellent reproducibility from the light portion to the shadow portion.

In the image reproduction of the present invention, the screen ruling of the reproduction image differs depending on the density level of the image to be reproduced. By doing this, the screen frequency of the light part is large,
That is, a fine screen can be obtained, and the number of screen lines in the shadow portion is small, that is, a coarse screen can be obtained, and an image reproduction with excellent reproducibility from the light portion to the shadow portion can be obtained. Such image reproductions may include monochromatic images and may even be color images. Further, the image reproduction of the present invention may be a printed matter, or may take the form of a printing plate or a color separation film for obtaining a printed matter. Furthermore, when forming an image by facsimile, by using a means such as changing the screen ruling of halftone dots according to the density of the image,
It may be an image reproduction by facsimile.

Various methods can be employed to obtain image reproductions having different screen rulings corresponding to the density levels of the present invention.

The first method is a method of performing divided exposure using a mask. In this method, first, a color separation film or a color original is used as an original to print a hard tone film such as a lith film to form a mask. In this case, a plurality of black and white mask films corresponding to the density level of the original can be obtained by adjusting the exposure amount during printing. Examples of the mask film include a mask film for exposing a density of 2.0 or more, a mask film for exposing a density of 1.0 to 2.0, and a mask film for exposing a density of 1.0 or less. The above three types may be prepared, or the density level may be divided more finely than this, or two types of mask films may be used. In this way, a plurality of mask films are combined with the original for each density level, and the photosensitive material is divided and exposed using a contact screen having an appropriate number of screen lines for each density level. By doing so, an image having different screen rulings corresponding to the density level of the original is printed on the photosensitive material. Image reproductions can be obtained by post-processing depending on the photosensitive material used. For example, if a lith film used for plate making is used as a light-sensitive material, a printing plate film can be obtained as an image reproduction by developing it. Also used to do. If a resist material for gravure plate corrosion is used as the photosensitive material, a resist is obtained by subjecting it to development processing and the like, and a printing plate or even a printed matter can be obtained using this.

Furthermore, if a printing original plate, such as a PS plate, a resin plate for gravure, a resin plate for letterpress, etc., on which a photosensitive resin has been applied as a photosensitive material is used, a printing plate is obtained as an image reproduction by development processing. It can also be used to obtain further printed matter.

As the second method, similar to the first method, a photosensitive material is divided and exposed using a mask film, but a method using a plate-making scanner can be mentioned.

Among the plate-making scanners, for example, D manufactured by Hell in West Germany
Some of them, such as those called C-300, further include a mask film in addition to the input drum and the output drum. A mask corresponding to the density level of the original as used in the first method is attached to this mask film, and a photosensitive material and a contact screen having a predetermined number of screen lines are used for the output drum, and only a predetermined density level is used. In this method, exposure is carried out, and then the mask and the contact screen are replaced by different ones so that portions of different density levels are exposed to carry out divided exposure.

In this case, when using a plate-making scanner capable of electronically forming halftone dots without using a contact screen, instead of replacing the contact screen, give control to change the screen ruling. Good.

A third method is a method of using a plate-making scanner, and a method of using a gradation correction function such as dropout of the plate-making scanner.

The drop-out function of the plate-making scanner is a function that does not output a portion of the document below a certain density, or outputs only a portion within the density range and does not output the upper and lower areas. By using this function, the original can be divided into predetermined density levels to separately expose the photosensitive material, and the screen ruling can be changed at this time, whereby an image with different screen ruling depending on the density level can be obtained. A duplicate can be obtained. The means for changing the screen ruling may be the same as in the case of the second method.

A fourth method is a method of applying a technique, which is used in a plate-making scanner, a facsimile, or the like, to digitally process pixel information to form an image with halftone dots. This method uses an image processing device such as a plate-making scanner or a facsimile having a function of setting a predetermined density level at a predetermined screen ruling. A screen ruling is set to 150 / inch, and a screen ruling below that uses an image processing apparatus having a function capable of setting the screen ruling to 300 / inch.

By doing so, it is possible to obtain an image reproduction represented by halftone dots or lines having different screen rulings according to a predetermined density level.

As described above in detail, according to the present invention, it is possible to provide an image reproduction represented by halftone dots or lines having different screen rulings corresponding to a predetermined density level, and thereby, a shadow from a light portion can be provided. It is possible to provide an image reproduction that is excellent in image reproducibility even in parts.

Claims (3)

[Claims] 1. A duplicate of an image having density gradation, wherein the image of the duplicate having density gradation has halftone dots or lines having different screen rulings corresponding to a predetermined density level. An image reproduction, characterized in that the screen frequency of said halftone dots or lines is smaller in the areas of high image density than in the areas of low image density. 2. The image reproduction according to claim 1, wherein the image reproduction includes a monochrome image or a color image.
The image reproduction described in paragraph. 3. The image reproduction according to claim 1, wherein the image reproduction is a printed matter.