JP3897947B2 - Image data processing method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an image data processing method for creating binary image data used in an image output apparatus.
[0002]
[Prior art]
In recent plate making operations, first, images and characters constituting a printed matter are laid out on a computer to create image data. The image data is subjected to RIP processing (Raster Image Processing) and converted to binary image data in a bitmap format, and then printed by an image output device such as a CTP device (Computer To Plate) or an image setter in the subsequent stage. A plate (or plate making film) is output. Generally, at the time of the RIP processing, the pattern is subjected to a shading process (screening) to express an image with halftone dots.
[0003]
In the next printing operation, printing is performed by a printing machine using the plate-making plate. Further, as described above, as the plate making work is digitally performed by the computer, the calibration work is also digitized. That is, a color calibration output has been obtained from image data directly RIP processed using an image output device such as an ink jet printer.
[0004]
On the other hand, in a general printed matter, a halftone dot is thickened due to the spread of ink, and a density change called so-called dot gain occurs. For example, it means a density change in which a halftone dot set at a density of 50% during plate making becomes a halftone dot of a density of 60% due to the spread of ink during printing. The amount of density change due to such dot gain depends on the type of printing apparatus and printing conditions such as ink and paper.
[0005]
Conventionally, in order to suppress the density change due to the dot gain, for example, in the case of a positive halftone image, a correction in which the halftone dot is thinned in advance at the plate making stage, so-called dot gain correction has been performed. In other words, the data correction is such that the halftone dot gradation is converted to a low value (ie, the halftone dot is reduced) in consideration of the thickening of the halftone dot at the time of printing when screening is performed by the RIP process. . For example, in the previous example, a halftone dot level that is corrected in advance to a halftone dot of 50% density at the time of plate making so that a halftone dot of 60% density is correctly set to a halftone dot of 60% density at the time of printing. Correction by key conversion is performed.
[0006]
[Problems to be solved by the invention]
As described above, correcting the gradation of halftone dots as dot gain correction is effective for halftone images, but cannot be used for solid images such as line drawings. For this reason, for example, thin lines such as black hair, ruby characters, and ruled lines of a person expressed by solid thin lines may become thick and print quality may deteriorate.
[0007]
On the other hand, when the above-described CTP device, ink jet printer, or the like is used as an image output device, dot gain correction must be applied to the image data in accordance with the printing characteristics of each image output device (or subsequent printing device). In this case, the RIP process is repeated with a different dot gain correction amount for each output to each image output apparatus, so that a relatively heavy RIP process has to be performed a plurality of times, and the process takes time. It was.
[0008]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an image data processing method capable of correcting dot gain not only in a halftone image but also in a solid image. Specifically, binary image data is processed by thickening / thinning in advance in accordance with the dot gain amount of the image output device (or subsequent printing device).
Another object of the present invention is to provide an image data processing method that requires only one RIP process in different image output apparatuses.
[0009]
[Means for Solving the Problems]
The invention according to claim 1 is an image data processing method for creating binarized image data for use in one or more image output devices, wherein a pattern, characters, etc. constituting a printed matter are laid out. A RIP processing step of converting the obtained multi-valued image data into binary image data by performing RIP processing after performing first dot gain correction by correcting the halftone gradation of the image ;
Performing a second dot gain correction by thickening / thinning the binary image data in accordance with a dot gain amount of a target image output device , and the first dot In the gain correction, the halftone dot gradation of the image is corrected according to the dot gain correction amount corrected in consideration of the second dot gain correction.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
First, before describing the embodiment of the present invention, an outline of a binary image thickening / thinning process will be described with reference to FIGS. 3 and 4. FIG. First, FIG. 3A shows one halftone dot composed of 13 dots of black pixels d as an example. If four pixels adjacent to a pixel d that is already black in this image are converted to black, the halftone dot is a dot halftoned by one dot around it as shown in FIG. 3B. Can be converted to (D1 is a fattened pixel)
[0013]
On the other hand, if all the four pixels adjacent to the pixel d that is already black are not black, the dot d is converted into white as shown in FIG. It can be converted into a halftone dot that has been subjected to a thinning process. (D2 is a thinned pixel)
[0014]
4A similarly shows a part of a thin line having a width of 3 dots, FIG. 4B shows a thin line with a thickened one dot, and FIG. 4C shows a thin line with a single dot. It is a thin line. In this way, for the binary image after the RIP processing, the image thickening / thinning processing can be performed on both the halftone image and the solid image. The present invention is characterized in that the dot gain at the time of printing is corrected using this thickening / thinning process.
[0015]
In the above example, one dot thickening / thinning processing is performed on the pixel of interest in four neighboring pixels, but the thickening / thinning amount can be varied in more detail by setting the conversion condition. . For example, as an example of changing the number of neighboring pixels to be thickened / thinned, when performing thickening / thinning processing on eight neighboring pixels or only pixels in a part of the neighboring pixels are converted. There are cases. It is also possible to thin out pixels to be thickened / thinned at a predetermined rate, or to perform thickening / thinning processing of 2 dots or more.
[0016]
(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a plate making system employing an image data processing method according to the present invention, and FIG. 2 is a flowchart showing an image data processing procedure in this plate making system.
[0017]
Referring to FIG. 1, the plate making system according to the present embodiment includes a DTP device 1 (Desk Top Publishing) that creates image data D1 by editing an image read by a scanner or the like and text input by a word processor or the like, and the DTP device. RIP processing device 2 that performs RIP processing on image data D1 created in step 1 to convert it to binary image data D2, and an image output device that outputs an image based on binary image data D2 converted by RIP processing device 2 3 and 4.
[0018]
The DTP device 1 is composed of a microcomputer provided with various input / output units, storage means, and the like, and creates image data D1 in which pictures and characters constituting a printed matter are laid out. The image data D1 is, for example, multivalued image data in the PostScript format or PDF format of Adobe Systems.
[0019]
The RIP processing device 2 is composed of a microcomputer equipped with various input / output units, storage means, and the like. The multi-valued image data D1 is RIP processed and converted into, for example, YMCK four-bit bitmap image data D2. To do. In the RIP process, the picture is screened and formed as a halftone dot image, and characters and the like are formed as a solid image. The RIP processing device 2 selectively sends binary image data D2 that has been RIPed to the image output devices 3 and 4. The same image data D2 is sent to any of the image output devices 3 and 4. Therefore, the RIP process can be performed once.
[0020]
The image output devices 3 and 4 are thickening / thinning processing units 5 and 7 each composed of a microcomputer for image data processing, and output units 6 and 8 for outputting an image to a target output object. Consists of. Specifically, as the image output devices 3 and 4, an image setter that performs scanning exposure on a plate-making film to form a four-plate original film of YMCK, or scanning exposure and laser processing on a printing plate. This corresponds to a CTP apparatus that produces four printing plates of YMCK, an ink jet printer that outputs color proofing with ink corresponding to the YMCK color, and the like. In the present embodiment, two image output devices 3 and 4 are connected, but one or three or more devices may be connected.
[0021]
The thickening / thinning processing units 5 and 7 perform the above-described thickening / thinning processing on binary image data. Here, the thickening / thinning amount is preliminarily calculated experimentally in the target image output apparatuses 3 and 4 in advance, and adjusted according to the measured dot gain amount. Note that when the image output devices 3 and 4 are CTP devices or the like and the created printing plate is printed under different printing conditions, the same image output devices 3 and 4 differ according to the printing conditions of the subsequent stage. Make the amount thicker / thinner.
[0022]
Next, the image data processing procedure according to the present invention will be described with reference to the flowchart of FIG. In the figure, first, in step S1, multi-valued image data D1 created by the DTP device 1 is subjected to RIP processing and converted into binary image data D2. In this RIP process, the pattern is screened, but dot gain correction by tone conversion of halftone dots as described in the prior art is not performed.
[0023]
In the next step S2, any one of the image output devices 3 and / or 4 to be output is designated, and binary image data D2 is output to the image output devices 3 and / or 4. In step S3, the thickening / thinning processing units 5 and 7 of the designated image output devices 3 and 4 perform thickening / thinning processing of the image data D2, and the corrected image data D3 (or D3). ') To convert. In the next step S4, an image is output based on the converted image data D3 (D3 ′).
[0024]
The steps S1 to S4 may be performed in parallel for each predetermined scanning line, but in this flowchart, each process is described separately for each step for easy understanding. .
[0025]
According to the above-described image data processing method, not only a pattern converted to a halftone image but also a solid image such as a character or a thin line is corrected for dot gain at the time of printing by thickening / thinning processing. be able to. In addition, since the same RIP processed image data D2 can be used for different image output devices that require dot gain correction, the number of RIP processes that require a relatively long processing time can be reduced.
[0026]
(Other embodiments)
In the first embodiment described above, there is an advantage that the same dot gain correction can be performed for the halftone image and the solid image, but all the corrections are uniform. Therefore, the halftone correction performed on the conventional halftone image can be performed more finely for each gradation. In this embodiment, a description will be given of an image data processing method capable of performing finer correction for a halftone image by using conventional dot gain correction together. Hereinafter, this embodiment has the following two.
[0027]
(Second Embodiment)
This will be described with reference to the flowchart of FIG. First, in step S11, dot gain correction by tone conversion of a conventional halftone dot is performed on a picture during binarization by RIP processing. That is, in this step S11, the image data is converted into binary image data subjected to dot gain correction as in the conventional case. On the other hand, in step S11, the area of the solid image portion is calculated from the layout information of the image data and is obtained as area data of the solid image area. In the next step S12, an output destination image output apparatus is designated, and the binarized image data is transmitted together with the area data of the solid image area. In step S13, thickening / thinning processing is performed only on the solid image area in accordance with the area data of the solid image area. In step S14, output is performed based on the processed image data.
[0028]
In the second embodiment, the dot image correction by the conventional gradation conversion is used in combination, so that the halftone image can be corrected more finely for each gradation than the first embodiment, and the solid image can be further improved. There is an advantage that correction can be performed independently. However, there is a limitation that RIP processing must be performed for each image output device because dot image correction is performed on a halftone image.
[0029]
(Third embodiment)
This will be described with reference to the flowchart of FIG. First, in step S21, an output destination image output apparatus is designated. Thereby, the thickness / thinning amount of the thickening / thinning process performed in step S24 described later is determined. In step S22, the correction amount of dot gain correction is corrected based on the thickening / thinning amount obtained above.
[0030]
That is, the dot image is first corrected in dot gain by tone conversion in the next step S23, and further corrected by fattening / thinning processing in the next step S24. Will be done. Therefore, in the dot gain correction in step S23, the correction amount of the dot gain correction is corrected in advance in step S12 so that the correction considering the next thickening / thinning process is performed.
[0031]
In the subsequent step S23, the dot image is dot gain corrected in accordance with the corrected dot gain correction amount, and the RIP processing of the image data is performed. The binarized image data is subjected to thickening / thinning processing for both the halftone image and the solid image in step S24. In step S25, an image is output using the processed image data.
[0032]
In the third embodiment, since the dot image is used together with the conventional dot gain correction, finer dot gain correction can be performed than in the first embodiment described above. Since the thickening / thinning process can be performed on all of the halftone image and the solid image, there is an advantage that it is not necessary to specify the solid image area as in the second embodiment. However, as in the second embodiment, a conventional dot gain correction is performed on a halftone image, and thus there is a limitation that RIP processing must be performed for each image output device.
[0033]
【The invention's effect】
In the present invention, dot gain can be corrected not only for a halftone image but also for a solid image by the thickening / thinning process. In addition, when the conventional dot gain correction based on halftone dot conversion is not used together, there is an effect that the RIP process can be completed once.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of a plate making system that can employ an image data processing method according to a first embodiment of the present invention.
FIG. 2 is a flowchart showing an image data processing method according to the first embodiment of the invention.
FIG. 3 is an explanatory diagram for explaining fattening / thinning processing for a binarized halftone image.
FIG. 4 is an explanatory diagram for explaining fattening / thinning processing for a binarized solid image.
FIG. 5 is a flowchart showing an image data processing method according to a second embodiment of the invention.
FIG. 6 is a flowchart showing an image data processing method according to a third embodiment of the invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 DTP apparatus 2 RIP processing apparatus 3, 4 Image output apparatus 5, 7 Thickening / thinning processing part 6, 8 Output part D1 Multi-valued image data D2 Binary image data D3, D3 'Thickening / thinning Image data after processing

Claims (1)

An image data processing method for creating binarized image data for use in one or more image output devices,
Multi-valued image data obtained by laying out patterns and characters constituting the printed matter is subjected to first dot gain correction by correcting the halftone gradation of the image, and then RIP-processed to obtain binary image data. RIP processing step to convert to
Performing a second dot gain correction by fattening / thinning the binary image data in accordance with a dot gain amount of a target image output device ;
Have
In the first dot gain correction, the halftone gradation of an image is corrected according to a dot gain correction amount corrected in consideration of the second dot gain correction .

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