JP3017248B2 - Image reproduction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an apparatus for reproducing an original image with halftone dots for printing plate making.

[Prior art]

As an image reproduction method in printing plate making, there is a method of reproducing an original image as a halftone image. When an image is reproduced by such a method, a technique of performing various processes on the original image data is adopted in order to obtain a desired quality in the halftone image. As one of the techniques, there is known a processing by an unsharp masking method for enhancing the sharpness by enhancing the edges of the original image data. That is, in the unsharp masking method, a portion where the density of the original image changes rapidly, for example, from the step edge portion as shown in FIG. 8A to the 2nd portion as shown in FIG. The second derivative (Laplacian) is obtained, and the second derivative is subtracted from the step edge by electric signal processing to add overshoot or undershoot to the portion, thereby enhancing the edge as shown in FIG. 8 (C). And improve the sharpness of the original image. Conventionally, halftone image data has been obtained by converting the original image data of which sharpness has been improved by the unsharp masking method into halftone dots.

[Problems to be solved by the invention]

However, in the unsharp masking method, the edge portion of the image data to be emphasized is determined uniformly, and it is usually impossible to perform any optional selective processing. Because the part of the original image data that is emphasized is
This is because, regardless of the content and structure of the image, it is determined only by emphasizing a sharp change in density by signal processing. Therefore, when halftone processing is performed on image data whose sharpness has been improved by the unsharp masking method as in the related art, if noise is included in the original image data, not only the edge portion but also the noise is emphasized. There is a risk of doing it. Further, the edge portion of the original image data emphasized as described above does not always coincide with the contour portion of the halftone image data, and there is a problem that the sharpness of the halftone image may not be sufficiently improved. Also, the unsharp masking method is not specific to halftone processing and is not always suitable for enhancing halftone image data. In order to improve the sharpness of the halftone image,
It is considered that the shape of the halftone dot itself may be partially deformed, but there has been no such technique in the past. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and has been made to provide an image reproducing apparatus capable of reproducing a halftone image in a sharper and higher definition in consideration of the characteristics of the halftone image. Make it an issue.

SUMMARY OF THE INVENTION The present invention relates to an image reproducing apparatus that reproduces an original image with halftone dots for printing plate making, and a halftone data creating unit that creates halftone image data from the original image; From the image, means for creating image data for edge extraction having a density corresponding to halftone dots, and extracting the edge of the original image from the created edge extraction image data, along the extracted edge, An edge extraction unit that creates a halftone dot deformation signal for cutting a part of halftone dots of the halftone image data; and a halftone dot of the created halftone image data, The above object has been achieved by providing a halftone dot data deforming section that clarifies edges by improving the sharpness of a halftone image by deforming by cutting with a dot. Further, the present invention provides an image reproducing apparatus that reproduces an original image with halftone dots for printing plate making, a halftone dot data creating section that creates halftone dot data from the original image, and converts the original image into halftone dots. Means for creating image data for edge extraction at an arbitrary density coarser than the corresponding density; interpolating the created edge extraction image data; extracting an edge of the original image from the interpolated image data; Along, an edge extraction unit that creates a halftone dot deformation signal for cutting a part of halftone dots of halftone image data, and a part of halftone dots of the created halftone image data, The above-mentioned object is also achieved by providing a halftone data deforming unit that performs deformation by cutting with a halftone dot deformation signal to clarify edges and improve the sharpness of a halftone image.

[Action]

According to the present invention, in an image reproducing apparatus, while generating data for a halftone image from an original image, an edge of the original image is extracted from the image data for edge extraction, and the halftone image data is extracted by the extracted edge. A halftone dot deformation signal for cutting a part of the halftone dot is created, and the image is deformed by cutting with the halftone dot deformation signal to clarify the edge and improve the sharpness of the halftone image. Therefore, since the edge portion of the original image and the edge portion of the halftone dot image can be matched with each other, it is possible to make sharper, more detailed image reproduction by utilizing the characteristics of the halftone dot image. In the edge extraction of the original image, it is possible to create edge extraction image data having a density corresponding to the dots constituting the halftone dots from the original image, and to extract edges using the edge extraction image data. it can. In this way, edges can be accurately extracted from the image data for edge extraction having a high pixel density. Also, edge extraction image data is created from the original image at an arbitrary density that is coarser than the density corresponding to the halftone dots, the created edge extraction image data is interpolated, and the edges of the original image are interpolated from the interpolated image data. Can also be extracted. This makes it possible to reduce the number of data to be processed when creating image data for edge extraction from the original image, and to speed up the processing. Further, if the density for creating the image data for edge extraction is the same as the density for creating the data for the halftone image, the image data can be input by scanning the original image once with one type of density.
Processing is simple and fast.

【Example】

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The first embodiment of the present invention is an image reproducing apparatus having a configuration as shown in FIG. As shown in FIG. 1, the image reproducing apparatus mainly includes an image data input unit 10, an edge extraction unit 12, a halftone data creation unit 14, a halftone data transformation unit 16, a gradation correction unit 20 and a dot data output unit 22. The image data input unit 10 is for creating and inputting image data from an original image. The input unit 10 receives, for example, color image data (cyan (C), magenta (M), yellow (Y), black (B
k) A color scanner for inputting can be used. In the embodiment, the image data for edge extraction processed by the edge extraction unit 12 is a halftone dot (for example, the fourth dot).
The data for the halftone image corresponding to the density corresponding to the density shown in FIG. ) Are different from each other because they have the density corresponding to the symbol G).
One that can be scanned once or one that can obtain image data of two different densities in one scan is used. This difference in density is determined by how many dots constitute a part of a halftone dot generated from one pixel of image data input by scanning in order to obtain dot image data. That is, in the embodiment, 1/4 halftone dot is created from one pixel of the image data, which is composed of 4 × 4 dots. For example, it is possible to make the sampling interval four times coarser than the sampling interval for obtaining data. The edge extraction unit 12 forms an edge of an image from the input image data for edge extraction, and extracts an outline of an original image from the edge image. The edge extraction unit 12 has a configuration shown in FIG. 2 in detail. are doing. That is, as shown in FIG. 2, the edge extraction unit 12 includes an edge extraction stage 12A, a contour extraction stage 12B,
C, and a rough feeling reduction stage 12D. The edge extraction stage 12A performs an edge extraction process of the original image, and scans the original image at a density of, for example, four times the density of pixels for obtaining dot image data, thereby obtaining edge extraction image data. For example, a method that extracts edges from the image data by a Laplacian-Gaussian filter technique can be used. The Laplacian / Gaussian filter applies a low-pass filter process to the edge extraction image to give a blur, and sets a zero cross point as a result of the spatial second derivative operation as an edge position. For example, let the zero cross point of the spatial second derivative as shown in FIG. 3 (C) of the step edge as shown in FIG. 3 (A) be the edge position. The edge strength is obtained from the result of the spatial second derivative operation, for example, from the gradient around the zero-cross point or the difference between the maximum value and the minimum value shown in FIG. 3B. The contour extraction stage 12B extracts a contour from the extracted edge image. For example, an image recognition unit that recognizes the contour from the edge image by image processing can be used. The halftone dot deformation signal creation stage 12C is for creating a halftone dot deformation signal for cutting a part of halftone image data generated from the original image along the contour extracted from the original image. . In this case, for example, a main part is selected from the contour image as the halftone dot deformation signal, and while identifying the direction of the contour, for example, a halftone dot having the fineness of a quarter dot as shown in FIG. A modified mask signal can be created. The roughness reduction stage 12D reduces sharpness of the halftone dot image by cutting sharp portions of the halftone dot deformation signal in order to suppress noise generated in the halftone dot image after cutting. The halftone image data creating section 14 halftone-processes the input image data by scanning the original image and creates halftone image data. For example, as shown in FIG.
Assuming that 8 × 8 dots per halftone dot and four pixels of the original image (one pixel is indicated by a reference symbol G in FIG. 4A) correspond to one halftone dot, one image data is represented by, for example, FIG. As shown in (B), halftone dot processing is performed with a screen function for each quarter dot to obtain halftone image data. In this case, the screen function of the halftone dot is also called a screen hill. This is for obtaining the resolution characteristics and gradation characteristics of an image. For example, in the case of FIG. 4 (B), the screen function is that of 4 × 4 dots for each quarter dot.
Further, the halftone image is an image binarized by the screen function described above, and is composed of halftone dots of various sizes in order to give an effect such that the image looks continuous when viewed at a normal reading / writing distance. Image The halftone dot data transformation unit 16 cuts out the halftone image data based on the halftone dot transformation signal created by the edge extraction unit 12. For example, by performing an AND operation on the halftone dot deformation signal and the halftone image data as shown in FIG. 5, each halftone dot passing through the contour is cut out. FIGS. 6A and 6B show examples of halftone image data before and after cutting. The tone correction unit 20 performs tone correction by increasing halftone dots in the range where the outline passes through the halftone image data after cutting. As a result, the gradation change due to the cutout is restored as much as possible. The halftone data output unit 22 outputs halftone image data after gradation correction. Hereinafter, the operation of the first embodiment will be described. In the first embodiment, first, in the input unit 10, the original image is extracted once at two types of densities (in the embodiment, the sampling pitch of the edge extraction unit 12 is set to / 4 of the halftone dot data creation unit 14). Scan and sample to capture image data. Alternatively, in the case where the input unit 10 can obtain image data having two different densities with different sampling pitches in one scan, for example, the image data sampled by scanning at a high density and the sampled image data can be obtained. Among them, data corresponding to the pitch corresponding to the difference in the sampling pitch is held (if it is 1/4 pitch, data for 4 scans is held), averaged, and resampled image data is taken. In this case, for example, monochrome (black and white) image data is taken into the edge extraction unit 12 as edge extraction image data.
For example, color (C, M, Y, Bk) image data is taken into the halftone dot data creating unit 14 as the original image data for the halftone image. Next, in the edge extracting unit 12, first, an edge of the original image data is extracted by the edge extraction stage 12A along the arrow shown in FIG. 2 from the acquired original image data. Next, the contour of the original image is extracted from the edge image extracted in the contour extraction stage 12B. Next, a halftone-deformation signal (for example, a halftone-deformation signal shown in FIG. 5) is created from the extracted contour in a halftone-deformation signal creation stage 12C, and the halftone image reduction stage 12D generates a halftone-dot image in response to the halftone-deformation signal. Processing for reducing the roughness after cutting the application data. As shown in FIG. 6 (B), the edge of the halftone image data is cut out using the halftone deformation signal after this processing to clarify the edge. At this time, in order to restore the gradation change due to the edge cutout as much as possible, the gradation correction unit 20 performs gradation correction by increasing the density of the halftone dots of the image so that the density in the range of the contour line is increased. The image data is output from the dot data output unit 22. Next, a second embodiment will be described. In the second embodiment, the outline is extracted from the edge image of the edge extraction image data sampled by scanning at a density corresponding to the halftone dot taken in from the input unit 10 in the first embodiment. On the other hand, as shown in FIG. 7, a second edge extraction unit 24 for extracting the contour of the original image from the edge image of the edge extraction image data scanned and sampled at a density lower than the density corresponding to the halftone dot. Is an image reproducing apparatus having the following. In the image reproducing apparatus according to the second embodiment, edges are extracted from monochrome image data as in the first embodiment. The second edge extraction unit 24 scans and samples the original image by the input unit 10 at the density set in the pixel density determination unit 28 by the sampling density instruction unit 26 such as a keyboard and a switch. An edge is estimated by combining the image data for use with the first edge extraction unit 12 by an interpolation operation to obtain an edge image and a contour of the image. The pixel density determining means 28 determines that a part of halftone dots generated from one pixel of halftone image data for obtaining halftone image data is composed of N × N dots. .., N times finer than the above, and instructs the input unit 10 to sample the image data. The other configuration is the same as that of the first embodiment, and the description thereof is omitted. In the image reproducing apparatus according to the second embodiment, cutout is performed on the created halftone image data using the contour extracted by the second edge extracting unit 24 in the same manner as in the first embodiment. According to the image reproducing apparatus of the second embodiment, the amount of image data to be scanned and sampled by the input unit 10 can be reduced. If the set value of the pixel density determining means 28 is 1 and is the same as the density for scanning the halftone image data, scanning the original image once with one type of density will complete the image data input. Easy and fast. In the first and second embodiments, the outline is extracted from the edge image and the halftone dot image is cut out. You may make it so. In the first and second embodiments, the roughness reduction processing is performed on the halftone dot deformed signal. However, it may be performed on the halftone dot image data after clipping or may be omitted.

【The invention's effect】

As described above, according to the present invention, an excellent effect that a sharper, clearer and more detailed image can be reproduced with a contour in consideration of the characteristics of a halftone dot image can be obtained. In addition, if the edge information can be interpolated, it is possible to prevent the image quality from deteriorating when the image is enlarged or reduced, and to improve the accuracy. Further, the present invention can be developed into a method of storing image data with good workability.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an image reproducing device according to a first embodiment of the present invention, FIG. 2 is a block diagram showing a detailed configuration of an edge extracting unit in the device, FIG. FIG. 4 is a diagram showing an example of a Laplacian-Gaussian filter process for explaining the operation of the first embodiment. FIG. 4 is a perspective view showing a screen function for original image data and an example of halftone image data. FIG. 5 is a plan view showing an example of a halftone dot deformed signal, FIG. 6 is a plan view showing an example of a cutout process of halftone image data, and FIG. 7 is a plan view of the present invention. FIG. 8 is a block diagram illustrating a configuration of an image reproducing apparatus according to a second embodiment. FIG. 8 is a diagram illustrating an example of unsharp masking for explaining a conventional image reproducing technique. 10: Input unit, 12: Edge extraction unit, 12A: Edge extraction stage, 12B: Outline extraction means, 12C: Halftone dot deformation signal creation stage, 12D: Roughness reduction stage, 14: Halftone dot Data creation unit, 16: Halftone data transformation unit, 20: Tone correction unit, 22: Halftone data output unit, 24: Second edge extraction unit, 26: Sampling density indicating means, 28 ... ... Pixel density determining means.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-38973 (JP, A) JP-A-61-262375 (JP, A) JP-A-62-272756 (JP, A) JP-A-57-1987 155541 (JP, A) JP-A-1-115273 (JP, A) JP-A-1-315883 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 1 / 40-1 / 409 H04N 1/46 H04N 1/60

Claims (2)

(57) [Claims] 1. An image reproducing apparatus for reproducing an original image with halftone dots for printing plate making, comprising: a halftone dot data creating section for creating halftone dot data from the original image; Means for generating image data for edge extraction having a corresponding density; extracting an edge of the original image from the generated edge extraction image data; and forming a halftone dot of the halftone image data along the extracted edge. An edge extraction unit that creates a halftone-deformed signal for cutting part of the halftone-dot data of the created halftone-image data, And a halftone data transformation unit for clarifying edges and improving the sharpness of the halftone image. 2. An image reproducing apparatus for reproducing an original image by halftone dots for printing plate making, comprising: a halftone dot data creating section for creating halftone image data from the original image; Means for creating image data for edge extraction at an arbitrary density coarser than the corresponding density; interpolating the created edge extraction image data, extracting edges of the original image from the interpolated image data, and extracting the extracted edges Along, an edge extraction unit that creates a halftone dot deformation signal for cutting a part of a halftone dot of the halftone image data, and a part of the halftone dot of the created halftone image data, An image reproducing apparatus, comprising: a halftone dot data deforming unit that deforms by cutting with a halftone dot deformation signal to clarify an edge and improve sharpness of a halftone image.