JPH0440168A - image reproduction device - Google Patents

Abstract

PURPOSE:To reproduce a high-quality picture by executing the processing of reducing the noise of a dot image data after extraction to a prepared dot deforming signal, extracting the edge of the dot image data by the dot deforming signal to which the reduction processing is executed, and correcting the gradation of the extracted dot image data. CONSTITUTION:A dot deforming signal preparing step 12B prepares the dot deforming signal for cutting one part of the dot image data. A rough feel reducing step 12C reduces the rough feel of a dot image by reducing the amount of operating to the dot at a separated part from the edge of the prepared dot deforming signal so as to suppress noise to be generated in the dot image after cutting. In this rough feel reducing step 12C, the unit of having the edge in the dot is selected for the unit of a 1/16 dot further to the dot deforming signal obtained by the deforming signal preparing step 12B. Since the cut part is small within the range of the 1/16 dot, the blank caused by cutting does not stand out and the rough feel can be prevented.

Description

[Detailed description of the invention] [Industrial application field]

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 reproducing an image using such a method, techniques are employed in which various types of processing are performed on the original image data in order to obtain desired quality in the halftone dot image. As one of these techniques, processing using an unsharp masking method is known, which emphasizes the edges of original image data and improves sharpness. That is, in the unsharp masking method, from a part of the original image where the density changes rapidly, for example, a step edge part as shown in FIG. By calculating the number of planes (Laplacian) and subtracting the number of two planes from the step edge using electrical signal processing, overshoot and undershoot are added to the part, as shown in Figure 10 (C). Emphasizes edges and improves the sharpness of the original image. Conventionally, original image data whose sharpness has been improved by this unsharp masking method is converted into halftone dots to obtain halftone image data. However, in the unsharp masking method, the edge portions of image data to be emphasized are uniformly determined, and usually it is not possible to perform arbitrary selective processing. This is because the portion of the original image data to be emphasized has no relation to the content or structure of the image, and is determined only by emphasizing the portion where the density changes rapidly through signal processing. Therefore, when performing halftone processing on image data whose sharpness has been improved using the unsharp masking method as in the past, if the original image data contains noise,
There is a risk that not only the edge portion but also the relevant noise will be emphasized. Furthermore, the edge portion of the original image data emphasized as described above does not necessarily match 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, unsharp
Masking methods are not unique to halftone processing and are not necessarily appropriate for enhancing halftone image data. Note that in order to improve the sharpness of a halftone dot image, it may be possible to partially deform the shape of the halftone dot itself, but there has been no such technique in the past. The present invention has been made to solve the above-mentioned conventional problems, and provides an image reproduction device that can reproduce an original image as a halftone image more sharply and in high detail by taking into account the characteristics of the halftone image. The task is to do so.

[Means for Achieving the Object 1] The present invention provides a device for reproducing an original image as a halftone image, including a means for creating halftone image data from the original image, and a means for extracting edges of the original image. means for creating a halftone deformation signal for cutting out halftone image data from the extracted edges; a noise reduction processing means for performing processing to reduce the noise; a means for cutting out the edges of the halftone image data using the halftone deformation signal subjected to the noise reduction processing; and a gradation of the halftone image data that has been cut out. The above object is achieved by providing means for correcting. [Function] In the present invention, in an image reproduction device, halftone image data is created from an original image, and edges of the original image are extracted, and halftone dots are used to cut out halftone image data from the extracted edges. A deformed signal is created, the created halftone dot deformed signal is subjected to processing to reduce noise in the halftone image data after cropping, and the halftone deformed signal subjected to the reduction processing is used to create the halftone dot image data. The edges of the image are cropped, and the tone of the cropped halftone image data is corrected. Therefore, since the edge portions of the original image and the edge portions of the halftone dot image can be made to match with high accuracy, the characteristics of the halftone dot image can be utilized to reproduce the image sharply and with high detail. Furthermore, if the halftone dot image data is simply subjected to the cutting process, the cut out portion will stand out as a white noise, and the edge portions of the halftone dot image will have a rough feel. In contrast, in the present invention, the portion where the halftone dots are cut out is, for example, shown in FIG. 4 (E) and FIG. 7 (B).
), the area that is cut out only near the edges is made smaller to eliminate the roughness. Furthermore, since the density of the halftone dots after cutting cannot be compensated even if the number of cutouts is reduced, in the present invention, for example, the pixel value is changed to make the halftone dot larger in anticipation of the cutout part, and the gradation is adjusted. Correct. Note that in the edge extraction of the original image, edge extraction image data with a density corresponding to the dots forming the halftone dots is created from the original image, and edges are extracted using this edge extraction image data. can. In this way, edges can be extracted with high precision from original image data with high pixel density. Also, the density is coarser than that corresponding to the halftone dots from the original image,
In addition, create image data for edge extraction with arbitrary density,
It is also possible to interpolate the created edge extraction image data and extract the edges of the original image from the interpolated image data. In this way, the number of data to be processed when creating image data for edge extraction from the original image can be reduced, and processing speed can be increased. Also, if the density for creating image data for edge extraction is the same as the density for creating original image data for halftone images, then the original image can be created with one type of density.
Since image data input is completed by scanning twice, processing is simple and speedy. [Embodiment 1] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. A first embodiment of the present invention is an image reproducing apparatus having a configuration as shown in FIG. As shown in FIG. 1, this image reproduction apparatus mainly includes an image data input section 10, an edge extraction section 12, a halftone data creation section 14, a halftone data transformation section 16, and an M tone correction section. 2
0, and a halftone data output section 22. The image data input section 10 is for creating and inputting original image data from an original image. The input unit 10 may be, for example, a color scanner for inputting color image data (cyan (C), magenta (M), yellow (Y), black<Bk)) from a color document for printing. In addition, in the embodiment, the image data for edge extraction processed by the edge extraction unit 12 includes halftone dots (for example, FIG.
) with a density corresponding to 9), and
The halftone image data processed by the halftone data creation section 14 has a density corresponding to a 1/4 halftone dot (for example, indicated by the symbol G in FIG. 5(A)), so there are differences between them. Therefore, for the image data input section 10, a device capable of scanning twice at different densities or a device capable of obtaining image data of two different densities in one scan is used. This difference in density is determined by how many dots constitute a portion of a halftone dot generated from one pixel of halftone image data scanned and input to obtain halftone image data. That is, in the embodiment, a 1/4 halftone dot is generated from one pixel of image data and is composed of 4 x 4 dots, so the sampling interval when obtaining data for a halftone image is equal to that of the edge extraction image. It can be, for example, four times coarser than the sampling interval at which the data is obtained. The edge extraction section 12 extracts the edges of an image from the input original image data, and has a detailed configuration shown in FIG. 2. That is, as shown in FIG. 2, the edge extraction section 12 includes an edge extraction stage 12B, a halftone deformation signal creation stage 12C, and a roughness reduction stage 12G. The edge extraction stage 12A performs edge extraction processing on the original image, and scans the original image at a pixel density that is, for example, four times as high as that used to obtain halftone image data to obtain original image data for edge extraction. For example, it is possible to use a method that extracts edges from edge extraction image data by manually applying a Laplacian-Gaussian filter. This Laplacian
The Gaussian filter applies low-pass filter processing to the original image to give it a blur, and uses the zero-crossing point of the result of the spatial quadratic differential operation as the edge position. For example, the edge position is the zero-crossing point of the spatial quadratic differential as shown in FIG. 3(C) of the step edge shown in FIG. 3(A). The edge strength is determined from the gradient around the zero crossing point and the difference between the maximum value and the minimum value, as shown in FIG. 3(B), from the result of the empty WA second-order differential calculation. The halftone deformation signal creation stage 12B creates a halftone deformation signal for cutting part of the halftone image data along edges extracted from the original image. Create this halftone deformation signal! lj, 12B, first, as shown in FIG. 4(A), from among the edges extracted by the edge extraction stage 12A, as shown in FIG. A unit corresponding to a portion of a halftone dot generated from image data (halftone image data), that is, 1/4 in the example
Select the main edges for creating the halftone deformation signal in halftone units. In this selection, an edge of a certain length (for example, 3 dots) or more crossing a 1/4 halftone dot is selected as the main edge, and the direction of the edge is determined from the way it crosses. In this way, since only the main edges are selected,
Noise is less emphasized. Next, as shown in FIG. 4(B), for example, the pixels A around the 1/4 halftone dot being processed are minute pixels corresponding to the dot resolution of the halftone dot.
The value of -P and information about the portion (indicated by diagonal lines in FIG. 4) where halftone dots are cut from the edge from the direction of the selected edge are obtained, and a halftone deformation signal is created for this portion. The roughness reduction stage 12C reduces the amount applied to the halftone dots in the portions away from the edges of the created halftone dot deformation signal in order to suppress noise occurring in the halftone image after cutting. This reduces the roughness of the surface. In this roughness reduction stage 12G, a fourth
As shown in Figure (C), a unit of 1/16 halftone dot is further selected, and a unit in which an edge exists is selected. A halftone deformation signal is created in which the selected unit portion is a cutout portion as shown in FIG. 4(D). FIG. 4(E) shows an example of halftone image data cut out by this halftone transformation signal. Figure 4 (E)
As shown in the figure, the cutout area is small because it is within the range of 1/16 halftone dot, and the whiteness caused by the cutout becomes less noticeable, thereby preventing the appearance of roughness. Here, the halftone image data creation section 14 shown in FIG.
In this method, image data (halftone image data) inputted by scanning an original image is subjected to halftone processing to create halftone image data. For example, as shown in FIG. 5(A), one halftone dot is 8×8 dots, and four pixels of the original image (one pixel is indicated by the symbol G in the figure) correspond to one halftone dot. For example, as shown in FIG. 5(B), the data is subjected to halftone processing using a screen function of 1/4 halftone dots to obtain halftone image data. In this case, the screen function for this halftone dot is also called a screen hill, and it provides a threshold value for binarizing the change in density of the original image for each dot of the 1/4 halftone dot, and determines the shape of the halftone dot and the halftone dot. It determines the resolution characteristics and gradation characteristics of the image. For example, in the case of FIG. 5(B), the screen function shows 4×4 dots for every 1/4 halftone dot. Also, the halftone image is
This is an image that has been binarized using the screen function described above, and is an image composed of halftone dots of various sizes to give an effect that looks like a series of RgI when viewed at a normal reading and writing distance. The halftone data transformation section 16 cuts out the halftone image data using the halftone transformation signal created by the edge extraction section 12. For example, halftone deformation (
By performing an AND operation on the mask signal and the halftone image data, each quarter halftone dot through which the contour passes is cut out. Examples of halftone image data before and after cutting are shown in Fig. 7 (A) and (B).
Shown below. The gradation correction unit 20 increases the density of the area where the contour line passes through the halftone image data after cutting out.
This is for correction. This is to compensate for the lack of gradation in the halftone dot data that cannot be compensated for by the roughness reduction process. For example, when the halftone dot image data after cutting is in the state shown in FIG. 4(E) or FIG. 7(B), first, the area of the cut halftone dot image is measured every 1/4 halftone dot. The area of the cutout portion of the halftone dot is determined from the difference between the area of the halftone dot image before cutting and the halftone dot image after cutting. A correction value for gradation correction is determined from the area of this cut-out portion. For example, the correction values shown in Table 1 below are used in accordance with the cut-out area. Table 1 Using the calculated correction values, for example, for the corresponding 1/4 halftone dot that is blurred in Figure 8 (A), increase the pixel value as shown in Figure 8 (B). Correct the pixel value so that the pixel value is between 0 and 255. Using this pixel value, halftone image data is regenerated, and for this halftone image data,
The halftone image data cut out by the halftone data transformation section becomes the halftone image data to be finally output. Note that the noise reduction processing in the roughness reduction stage 12G has a gradation correction function as well as noise reduction, and works to restore gradation changes due to clipping as much as possible together with the gradation correction by the WiWA correction section 20. The dot data output section 22 outputs line dot image data after gradation correction. Next, the operation of the first embodiment will be explained. In this first embodiment, first, the input section 10 inputs the original image once at two different densities (in this embodiment, the sampling pitch of the edge extraction section 12 is set to 1/4 of that of the halftone data creation section 14). Scan, sample, and capture image data. Alternatively, if the input unit 10 is capable of obtaining image data of two types of densities with different sampling pitches in one scan, for example, by scanning at a high density,
The sampled image data and the data for the pitch corresponding to the difference in sampling pitch (if the pitch is 1/4 pitch, the data for 4 scans are retained), are averaged, and the resampled image data is take in. In this case, the edge extraction unit 12 receives, for example, monochrome (black and white) image data as image data for edge extraction, and the halftone data creation unit 14 receives, for example, color (C, MlY, Then, in the edge extraction section 12, edges of the original image data are first extracted at an edge extraction stage 12A along the arrows shown in FIG. 2 from the imported original image data. Then, from the extracted edges, a halftone dot transformation signal (for example, the halftone transformation signal shown in FIG. 4(A), <8) is created at the halftone dot transformation signal creation stage 12B. The roughness reduction stage 12G reduces the roughness of the halftone image data after cutting the halftone image data by setting the cutout portion near the edge, as shown in FIGS. 4(C) and (D), for the halftone deformation signal. Apply processing. Using the halftone dot deformation signal after this processing, the edges of the halftone dot image data are cut out and clarified as shown in FIGS. 4(E) and 7(B). At this time, in order to restore the gradation change due to edge cutting as much as possible, the gradation correction section 20
), the pixel values of the halftone dots near the edges are increased to perform gradation correction on the halftone dot image data after cutting out. Next, the halftone data output unit 22 outputs the corrected halftone image data and stores it in a storage unit (not shown) as required. Next, a second embodiment will be described. This second embodiment corresponds to the halftone dots taken in from the input section 10 in the first embodiment! In contrast, as shown in Figure 9, the edge image of the original image was extracted from the sampled image data for edge extraction by scanning at a The image reproducing apparatus includes a second edge extraction section 24 that extracts edges of the original image from scanned and sampled image data for edge extraction. In the image reproducing apparatus of this second embodiment, edges are extracted from monochrome image data as in the first embodiment. The second edge extraction section 24 scans and samples the original image by the input section 10 at a density set in the pixel density determination section 28 by the sampling density instruction section 26 such as a keyboard or switch, and extracts the obtained edges. The first edge extracting section 12 performs an interpolation calculation on the image data for extraction to estimate edges, thereby obtaining an edge image and, ultimately, the contour of the image. If a part of a halftone dot generated from one pixel of halftone image data for obtaining halftone image data is composed of NXN dots, the pixel density determining means 28 is configured to 1.2.3...N
This command instructs the input unit 10 to sample the image data in even greater detail. Note that the other configurations are the same as the first
Since this is the same as the embodiment, the explanation thereof will be omitted. In the image reproducing apparatus of the second embodiment, the generated halftone image data is clipped using the edges extracted by the second edge extraction section 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 section 10 can be reduced. Furthermore, when the set value of the pixel density determining means 28 is 1x, which is the same as the density at which the halftone image data is scanned, the image data input is completed by scanning the original image once at one type of density, so that the processing becomes easier and faster. Note that in the first and second embodiments, the halftone image is cut out using the edges of the image, but the present invention is not limited to using the edges in this way, and the image is cut out from the edges using an image processing method. You may also obtain a contour and cut out using this contour. Further, in the first and second embodiments, the roughness reduction process is performed on the halftone deformation signal, but it can be performed on the halftone image data after cutting out. (Effects of the Invention) As explained above, according to the present invention, it is possible to obtain an excellent effect of being able to reproduce sharper, clearer, and more detailed images of edges in consideration of the characteristics of halftone images. If the edge information can be interpolated, it is possible to prevent image quality deterioration during image enlargement or reduction and improve reproduction accuracy.Furthermore, it can be developed into an image data storage method with good processability.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an image reproduction device according to a first embodiment of the present invention, FIG. 2 is a block diagram showing the detailed configuration of an edge extraction section in the device, and FIG. A diagram showing an example of Laplacian-Gaussian filter processing for explaining the operation of the first embodiment. FIG. 4 also shows an example of halftone dots after halftone deformation signal creation roughness reduction processing and cropping. 5 is a perspective view showing an example of a screen function for original image data and halftone image data; FIG. 6 is a plan view showing an example of a halftone deformation signal; FIG. Similarly, FIG. 8 is a plan view showing an example of the gradation correction process of the halftone image data after the cutting process, and FIG. FIG. 10 is a block diagram showing the configuration of an image reproducing apparatus according to a second embodiment of the present invention. FIG. 10 is a diagram showing an example of unsharp masking for explaining a conventional image reproducing technique. 20... Gradation correction section, 22... Halftone data output section, 24... Second edge extraction section, 26... Sampling density instruction means, 28... Pixel density determination means.

Claims (1)

[Claims] (1) A device for reproducing an original image as a halftone image, which includes a means for creating halftone image data from the original image, a means for extracting edges of the original image, and a means for reproducing halftone image data from the extracted edges. means for creating a halftone deformation signal for cropping dot image data; and noise reduction processing means for performing processing on the created halftone deformation signal to reduce noise in the halftone image data after cropping. and means for cutting out edges of the halftone image data using a halftone deformation signal subjected to noise reduction processing, and means for correcting the gradation of the halftone image data that has been cut out. Featured image reproduction device.