JP4640647B2 - Image processing method, image processing apparatus, and image forming apparatus - Google Patents

Description

  The present invention relates to an image processing method, an image processing apparatus, and an image forming apparatus. More specifically, a halftone dot of a predetermined size corresponding to the intensity of the input image signal is used to record a halftone image on an image recording medium in an electrophotographic method or an ink jet method. The present invention relates to a binarization processing technique that represents a halftone image in a pseudo manner.

  As one technique for representing a halftone image using binary data, forming colored dots called halftone dots (a set of individual halftone dot output dots) of a predetermined size corresponding to the intensity of the input image signal A mechanism of binarization processing (in particular, also called halftone processing) that reproduces the density of a halftone image in a pseudo manner according to the size of the colored dots is known.

  For example, a color printed matter uses four printing plates for four color inks of yellow (Y), magenta (M), cyan (C), and black (K) to record four color inks. It is created by sequentially overprinting on a medium (printing paper). On the printing plate, a halftone image is recorded in which the density of a continuous tone image of a color original is reproduced by a set of many minute halftone dots.

  FIG. 12 is a diagram showing an example (A) of such a halftone process and an example (B) of a halftone dot generated by this halftone process. For example, when generating a halftone image in a printing technique using an electrophotographic system, as shown in FIG. 12A, a multi-value image signal (multi-value data) representing the density of an image of a color document is given as a predetermined value. A binarized recording signal is generated by comparing with screen pattern data (each threshold value data of the threshold value matrix) with a comparator.

  Further, the binary recording signal is used as an on / off signal (halftone signal) for each recording pixel, and the exposure light beam is on / off controlled in accordance with the halftone signal, thereby allowing an image carrier (for example, a photoconductor). A halftone image is exposed on the drum). After that, the image (latent image) on the image carrier is visualized as a toner image by spraying toner (powder) onto the image carrier, and the toner image is transferred and fixed on an image recording medium. By doing so, an image having a halftone dot of a size corresponding to the density as shown in FIG.

  Here, when halftone dots are used in the electrophotographic technique, generally, one or two toners are stacked at a height of about 1.5 on average, and reach 10 or more microns before fixing. This is often determined from the amount of toner necessary for the maximum density, and the amount of toner is excessive for halftone reproduction. In particular, since the halftone dot size is reduced in the highlight portion (low density region), the probability of occurrence of this problem is increased.

  In the case of color reproduction, there is a toner transfer step, and the higher the halftone dot toner image, the greater the image quality deterioration during transfer and the thinner the halftone dot toner image. Furthermore, in multiple transfer for color reproduction, attention must be paid to image deterioration during transfer. However, it is difficult to achieve both the toner amount necessary for the maximum density and the toner amount suitable for dot reproduction.

  Further, an unfixed toner image of several tens of microns is crushed to several microns after fixing. Density reproduction by toner occurs when toner fixed on a sheet absorbs light. In order to improve the light absorption efficiency, it is necessary to efficiently expose the color material containing the toner layer with a thin toner layer to light. However, as described above, in the halftone dot structure for halftone reproduction, the toner layer is often excessively thick, and even the toner having little contribution to light absorption exists on the paper.

  On the other hand, in the printing technology that uses ink such as an ink-jet method as a color material, the dot dot gain is used to adjust the dot dot thickness and adjust the transferability of the ink (color material). Techniques for controlling the amount of adhesion are disclosed in Patent Documents 1 and 2.

Special table 2003-500940 gazette US Pat. No. 6,532,082

  For example, the mechanism described in Japanese Patent Laid-Open No. 2004-228620 is suitable for the purpose of reducing the dot gain of a stochastic screen (established printing) by appropriately thinning out the binarized image once on the stochastic screen and appropriately adjusting the density. Technology to lower.

  Further, the mechanism described in Patent Document 2 is a technique that presumes halftone dots of clustered dots and appropriately lowers the density by probabilistic thinning out an image binarized by normal halftone dot processing.

  More specifically, in the mechanism described in Patent Document 1, for a stochastic screen called FM screen, and in the mechanism described in Patent Document 2, for a regular halftone screen called AM screen, The dot gain and the ink amount are adjusted by aperiodically thinning out some dots (halftone dots) each forming a halftone dot. That is, the generation of halftone dots and the generation of void dots are made asynchronous.

  However, an FM screen such as the mechanism described in Patent Document 1 reproduces the density with a density of minute dots that cannot be visually recognized (about 30 microns or less). The dots may be thinned out, and the color pixel area may become too small, leading to unstable dot reproduction.

  On the other hand, if some dots of halftone dots are non-periodically thinned out with an AM screen such as the mechanism described in Patent Document 2, there are cases where the dots are thinned out inside the halftone dots and thinned out at the halftone dot outlines. This may cause a phenomenon in which the halftone dots to be reproduced are different from each other and cause image noise. Also, when there are many pixels to be thinned out inside the halftone dots, there is a function of thinning the coloring material in the halftone dots, but when many thinnings are made in the outline of the halftone dots, the size of the halftone dots is reduced. Since the function of thinning the colorant in the halftone dot portion is reduced, the effect of thinning the halftone dot cannot be expected. In particular, since the halftone dot size is small in the highlight portion (low density region), the probability that these problems will occur increases.

  The present invention has been made in view of the above circumstances, and is simulated using halftone dots regardless of printing methods such as an electrophotographic method using powder as a color material or an ink jet method using ink as a color material. In particular, an object of the present invention is to provide a mechanism capable of thinning the colorant layer in the halftone dot portion while preventing the deterioration of the image quality when reproducing the density of the halftone image.

  The image processing method according to the present invention forms halftone dots represented by a set of one or a plurality of output dots corresponding to the intensity of the input image signal, and reduces the amount of coloring material in the halftone dots. This is an image processing method for generating a pseudo halftone image by making some dots forming halftone dots virtually non-output dots when the intensity of the image signal exceeds a predetermined value. In addition, while maintaining the outline dots, which are output dots that contribute to the outline formation of the halftone dots, as the output dots, some of the dots inside the outline dots are made virtually non-output dots. That is, the generation of halftone dots and the generation of void dots are synchronized, and the void dots are formed inside the halftone dots.

  The image processing apparatus according to the present invention is an apparatus suitable for carrying out the image processing method according to the present invention, and has a halftone dot outline when the intensity of the image signal is in a predetermined range exceeding a predetermined value. The binarization processing unit is configured to make a part of the dots inside the outline dot practically non-output dots while maintaining the outline dot forming the output dot.

  An image forming apparatus according to the present invention is an apparatus having a function of an image processing apparatus suitable for carrying out the image processing method according to the present invention, wherein the image signal intensity exceeds a predetermined range. A binarization processing unit that maintains the outline dots forming the outline of the halftone dots as output dots, and converts some of the dots inside the outline dots to virtually non-output dots, and the binarization process unit And an image recording unit for forming a halftone image having virtually no output dots in the halftone dots based on the binarized data generated by the above.

  The inventions described in the dependent claims define further advantageous specific examples of the image processing apparatus and the image forming apparatus according to the present invention.

  For example, as the original halftone dot shape to be processed in the present invention, a so-called dot halftone dot (so-called dot screen) in which output dots grow in a substantially circular shape according to the density, or an input image signal is used. There is a linear halftone dot (so-called line screen) having a structure in which halftone dots are linearly connected in a region having a predetermined density or higher. The dot screen has a simple halftone dot shape, but it is vulnerable to disturbances during image formation and color moire. On the other hand, the line screen has an advantage that it is resistant to disturbance during image formation and color moire.

  When the present invention is applied to dot-like halftone dots, ring-like halftone dots are obtained. When the present invention is applied to a linear halftone dot, for example, non-output dots are arranged in a linear manner within the linear halftone dot within a predetermined density range, that is, voids grow in the linear structure. When the double line structure is used and when the non-output dots are kept isolated in the linear halftone dots, that is, when the non-output dots are not connected linearly in the linear halftone dots, These two methods can be representatively taken. The latter has better line structure reproducibility.

  In addition, on the electronic data representing the halftone dots, a part of the dots inside the outer dots may be set as true non-output dots, that is, a pure electronic mechanism that thins out the image recording signal inside the halftone dots. Or based on the binarization data produced | generated by the binarization process part, it is good also as a mechanism which modulates the recording energy of the non-output dot inside a halftone dot outline so that a coloring material may fall.

  It should be noted that the functional part related to the binarized data processing in the image processing apparatus and the image forming apparatus according to the present invention can be realized by software using an electronic computer (computer), and a program for this and a program stored therein are stored. It is also possible to extract the recorded medium as an invention. The program may be provided by being stored in a computer-readable storage medium, or may be provided by distribution via wired or wireless communication means.

  According to the present invention, only when the intensity of the image signal is within a predetermined range exceeding a predetermined value, while maintaining the outline dot forming the outline of the halftone dot as the output dot, some dots inside the outline dot are actually Since the upper non-output dots are formed, it is possible to reduce the thickness of the coloring material inside the halftone dots without destroying the outline shape of the halftone dots due to toner or ink.

  As a result, the colorant at the halftone dots can be effectively thinned without causing image quality degradation. Moreover, since the ratio of the amount of the coloring material that contributes to light absorption increases, the consumption of the coloring material can also be reduced. In addition, since the generation of halftone dots and the generation of void dots are synchronized, control when forming void dots inside the halftone dots is simplified.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Overall Configuration of Image Forming Apparatus; First Embodiment>
FIG. 1 is an overall view of an image forming apparatus according to a first embodiment, focusing on an image processing unit (image processing apparatus) and an image recording unit related to binarization processing in a printing apparatus such as an electrophotographic system or an inkjet system. It is a figure which shows an outline. As illustrated, the image forming apparatus 1 according to the first embodiment includes a color separation signal generation unit 10, a binarization processing unit 20, a binary data storage unit 30, an image recording unit 40, and a profile switching command unit. 50. The color separation signal generation unit 10, the binarization processing unit 20, and the binary data storage unit 30 constitute an image processing unit (image processing apparatus) related to binarization processing.

  The color separation signal generation unit 10 receives an image of a relatively high bit number (for example, 8 to 10 bits) from an image input unit (not shown) provided on the preceding stage or an image input terminal such as a personal computer connected via a communication interface. Data Din is acquired for each color component such as R (red), G (green), B (blue), and the image recording unit 40 processes image data Din_R, Din_G, Din_B for each color component. For example, it is converted into color separation data (hereinafter referred to as multivalued image data DMV) for each color component such as C (cyan), M (magenta), Y (yellow), K (black) corresponding to the toner color. For example, multi-bit digital data R, G, B of several bits are converted into multi-value digital data C, M, Y, K of the same several bits. For such color conversion processing, for example, processing steps such as RGB data → Lab data → YMCK data are employed.

  It should be noted that in the previous stage or subsequent stage of the color separation signal generation process (up to the previous stage of the binarization process), detailed description is omitted, but background removal processing, scaling processing, contrast adjustment (density adjustment) processing, and color correction processing. Predetermined image processing (preprocessing) such as filter processing, TRC (Tone Reproduction Control) correction processing (also called tone correction processing), and the like is performed. The details of each processing itself are the same as those in the prior art, and the description thereof is omitted here.

  The binarization processing unit 20 generates binarized data (1-bit data) obtained by subjecting each of the input multi-value image data DMV_C, DMV_M, DMV_Y, and DMV_K to screen processing. For example, multi-value digital data C, M, Y, and K, which is multi-value image information having a density gradation, are binarized and recorded in a pseudo manner to represent the density of a halftone image by the size of colored dots called halftone dots. A signal Dout is generated and stored in the binary data storage unit 30.

  The image recording unit 40 includes a marking engine unit 44 that reads the binarized recording signal Dout generated by the binarization processing unit 20 from the binary data storage unit 30 and performs image recording processing. The marking engine unit 44 may use an electrophotographic system in which, for example, toner is used as a color material, electrostatic latent image formation by exposure and subsequent development, transfer, and fixing are performed, or ink is used as a color material. Various types such as those using the ink jet method used for the printing, or making the printing plate and transferring the ink to the recording paper using the plate (for example, the lithography method) Can be used.

<Configuration of Binarization Processing Unit; First Embodiment>
FIG. 2 is a diagram illustrating a configuration of the binarization processing unit 20 (the binarization processing unit 20 of the first embodiment) used in the image forming apparatus 1 of the first embodiment. 3 and 4 are diagrams for explaining basic characteristics of the void formation processing in the binarization processing unit 20 of the first embodiment.

  Here, FIG. 3 is a diagram illustrating an example of a gap size profile indicating characteristics of threshold value data for gap formation used in the gap formation processing of the present embodiment. FIG. 4 shows an image (A) generated by normal binarization processing, and images (B) and (C) generated using the gap size profile shown in FIG. 3 in the processing of this embodiment. It is a figure which shows an example. In any case, the binarization processing unit 20 shows a case where a dot-shaped halftone dot in which output dots grow in a substantially circular shape according to the density is to be processed.

  3A and 3B, the concentrations C1 and C3 are concentrations that provide a low-density side void formation start point, and the concentrations C2 and C4 are concentrations that provide a high-concentration side void formation start point. Further, the concentration Ccnt in FIG. 3B is the concentration that gives the maximum value of the number of voids, in other words, the concentration at which the number of voids starts to increase and decreases. In particular, it represents a halftone dot output from the first comparison processing unit 21 shown in FIG. 2 when the intensity (corresponding to the density of the input image) of the multivalued image data DMV representing the input image is shifted from the low intensity side. The binarized data is set to the first value that becomes all output dots.

  The densities C1 and C3 that give the low-density side void formation start point are set while maintaining the outline of the halftone dots formed by a set of black dots (output dots) as black dots (output dots). It may be considered indispensable to arrange white dots (no output dots) on the screen. On the other hand, the densities C2 and C4 that give the high density side void formation start point are for arranging white dots (no output dots) in the halftone dots only in the intermediate density range, which is essential for the present invention. It is not a thing. The range from the density C1, C3 that gives the low density side void formation start point to the maximum density Cmax may be the density range of the processing target in which white dots (no output dots) are arranged inside the halftone dots.

  In contrast to the conventional example, the binarization processing unit 20 of the first embodiment provides a plurality of sets of comparators and threshold matrixes for binarization, and 2 output from each comparator. The present invention is characterized in that a plurality of arithmetic processors for logically calculating value data are provided. Each pair of the comparator and the threshold matrix is a module that can generate the same halftone dot structure, but the threshold matrix values are characterized.

  Specifically, as shown in the figure, the binarization processing unit 20 of the first embodiment refers to three comparisons that perform comparison processing for binarization with reference to multi-value data to be processed and a threshold matrix. It is provided with processing units 21, 22, 23, two binary operation processing units 26, 27 for performing a logical operation on binary data output from the comparison processing units 21, 22, 23, and a threshold matrix storage unit 29. Has been.

  The first comparison processing unit 21 corresponds to a first halftone image generation unit. In addition, the second and third comparison processing units 22 and 23 and the first binary calculation processing unit 26 constitute a second halftone image generation unit. In addition, the second and third comparison processing units 22 and 23 and the first and second binary operation processing units 26 and 27 include the halftone dots generated by the first comparison processing unit 21 within the halftone dots. In order to maintain the outline of the dots, a void formation processing unit 28 is formed that forms voids in the center of the halftone dots.

  Note that an algorithm for generating a halftone image in the second halftone image generation unit configured by the second and third comparison processing units 22 and 23 and the first binary calculation processing unit 26 is a threshold value to be referred to. Although the matrix MTX1 is different, all of them are basically the same as the algorithm for generating the same halftone image (black dot) as the first comparison processing unit 21 (that is, the second halftone image generation unit). is there.

  The threshold value matrix storage unit 29 outputs a threshold value corresponding to each coordinate value in the matrix. As an example, the threshold matrix storage unit 29 includes a halftone dot profile storage unit 29a and a gap profile storage unit 29b.

  The halftone dot profile storage unit 29a stores basic profile data for forming halftone dots. Specifically, the halftone dot size corresponding to the density of the input image, in other words, profile data that defines the density of the input image that generates the halftone dots, is a threshold value for halftone dot formation used in the halftone dot forming process. A first threshold value matrix MTX1 that provides a halftone dot size profile consisting of a set of data is stored. Basically, a dot pattern similar to the conventional halftone dot growth can be output, but within the unit halftone dot region until the density of the input image reaches the transition point density Ccnt from “0”. The difference is that the number of output dots is gradually increased, and after the transition point density Ccnt, all the dots in the unit dot area are output dots.

  The gap profile storage unit 29b stores gap data that defines the gap size corresponding to the density of the input image, in other words, the density of the input image that generates the gap. Specifically, the second and third threshold matrixes MTX2 and MTX3 are stored which give a gap size profile that is a set of gap formation threshold data used in the gap forming process of the present embodiment.

  Here, the gap size profile data (that is, threshold data) stored in the gap profile storage unit 29b enables the gap formation processing unit 28 to generate a halftone dot having a gap of a size according to the gap size profile data. For.

  For example, the second threshold value matrix MTX2 mainly defines the gap size on the low density side in the intermediate density range of the multi-value image data DMV, and the third threshold value matrix MTX3 mainly contains the multi-value. The void size on the high density side in the intermediate density region of the image data DMV is defined, and the void size in the entire intermediate density region of the multi-value image data DMV is defined by combining them. In the first embodiment, “combination of both” actually means logical synthesis of the comparison processing results with reference to the threshold matrixes MTX2 and MTX3.

  Basic gap size profile characteristics include a halftone dot (black dot / output dot) that forms a halftone dot when the input density exceeds the specified density, and white dots (no output dots). By forming, the amount of the coloring material of the whole halftone dot portion can be reduced. In other words, by preventing the formation of voids until the input density exceeds a predetermined concentration, the characteristics are set such that voids are not formed in the minute dots that are collected (clustered). If voids are generated in the highlight area where the dot size is small, the reproducibility of halftone dots will deteriorate, but this problem can be solved by creating voids by specifying the density of the void formation start point to be somewhat high. To do.

  In particular, as shown in the upper right of FIG. 3A, in the unit halftone dot region, the outermost vertical / horizontal / diagonal outputs that maintain the halftone dot outline, that is, contribute to the halftone dot outline formation. While maintaining the dots (hereinafter also referred to as outline dots) as output dots as they are, some of the dots inside the outline dots are changed to true no-output dots to form voids. In other words, the amount of the coloring material in the outline portion of the halftone dot is maintained at a predetermined amount, and the amount of the coloring material inside can be appropriately reduced from the predetermined amount.

  In addition, when a plurality of non-output dots are formed inside the outline dots, if the non-output dots are isolated within the outline dots, pixels to be thinned out are scattered within the halftone dots, and the halftone dot colorant is thinned. The effect may fade. In order to avoid this, it is preferable that a plurality of non-output dots are connected and gathered together as much as possible without being isolated. In addition, if there are halftone dot output dots in a cluster of non-output dots, output dots are scattered, and therefore it is preferable to form a cluster with only non-output dots. Furthermore, from the viewpoint of maintaining the contour, it is preferable that the shape of the cluster of non-output dots is as similar as possible to the contour shape of the halftone dots.

  As an example, the output dots are usually increased so that a set of black dots (output dots) has a substantially circular shape, and a halftone dot of a size corresponding to the density is formed. It is preferable that the number of non-output dots is gradually increased from the center of the halftone dot so that the recording signals (output dots) are thinned into a substantially circular shape, that is, the set of non-output dots has a substantially circular shape. For example, when four non-output dots are formed in a halftone dot, two non-output dots are arranged in the vertical and horizontal directions instead of arranging the four non-output dots in one row in the vertical, horizontal, or diagonal directions. Good. When the entire “halftone dot with voids” that is the final product is viewed, the internal output dots are converted into non-output dots (thinned out) so that the output dots are arranged in a substantially ring shape.

  For example, the gap profile storage unit 29b stores profile data according to one or both of the gap size fixing method shown in FIG. 3A and the gap size variable method shown in FIG. Note that the value of the gap size b in FIG. 3A is an example, and a plurality of profiles in which the value of the gap size b is variously changed may be prepared. Similarly, the characteristic line in FIG. 3B is an example, and a plurality of profiles in which the degree of change (including the maximum value) of the characteristic line is variously changed may be prepared. In any case, it is only necessary to have a certain correspondence between the input image density and the gap size.

  In addition, when a plurality of these profiles are stored, in practice, any one of them is selected and used based on a user instruction via the profile switching command unit 50 according to the application. By changing the profile to be used, it is possible to easily generate a halftone image having gaps with different characteristics.

  Here, the gap size fixing method is a method in which a gap of a constant size b0 is formed at almost the center in a halftone dot within a certain range (C1 to C2) of the intermediate density region of the density value of the multi-value image data DMV. . On the other hand, the gap size variable method is a fixed range (C3 to C4) in the middle density range of the density values of the multi-value image data DMV, so that the gap size gradually increases and then gradually decreases after reaching the maximum value. As shown by a solid line in FIG. 3B, the gap size is dynamically (substantially continuously) changed according to the concentration.

  In the case of the fixed gap size method, it is only necessary to specify one type of gap size b0 for a certain range (C1 to C2) of the intermediate concentration range, but the generation mechanism is not clear. There is a case where a pseudo contour is generated at the gap generation position. As one method for solving this problem, a gap size variable method is employed in which a different gap size is specified for each concentration.

  In addition, when a relatively large (smaller than halftone) void is formed in a relatively small halftone dot, that is, when there are too many pixels to be thinned out inside the halftone dot, the colorant at the halftone dot portion is thinned. Is too strong. In order to avoid this problem, with respect to the change characteristics of the gap size from the concentration C1, C3 onwards, which gives the gap formation start point on the low and high concentration side, to the transition point concentration Ccnt, it is preferable to increase the gap size slowly at the rise. . Needless to say, in order to give such characteristics, a gap size fixing method is adopted.

  The solid line in FIG. 3B shows a smooth curve so that the characteristic line changes almost continuously. However, when the gap is actually formed in the halftone dot, a threshold of a predetermined size is used. Since a certain dot in the matrix is hit or not hit, it becomes a multi-stage characteristic.

  In addition, as shown by a dotted line in FIG. 3B, as an intermediate between the gap size fixing method and the gap size variable method, the gap size is within a certain range of the intermediate density region of the density value of the multi-value image data DMV. It is also possible to adopt a method in which the gap size is changed in several steps in accordance with the concentration so that gradually increases and reaches a maximum value.

  Each comparison processing unit 21, 22, 23 is an example of a density / threshold comparison unit, and is held in multi-value image data DMV representing the density of the input image, that is, the density of the input multi-value image, and the threshold matrix storage unit 29. Each threshold value matrix MTX1, MTX2, MTX3 is compared with each threshold value to output a binary image.

  For example, the first comparison processing unit 21 compares the multi-value image data DMV (Multiple Value) to be processed with the first threshold value matrix MTX1. The second comparison processing unit 22 compares the multi-value image data DMV to be processed with the second threshold value matrix MTX2. The third comparison processing unit 23 compares the multi-value image data DMV to be processed with the third threshold value matrix MTX3.

  The first binary calculation processing unit 26 includes the second binary data Do2 output from the second comparison processing unit 22, and the third binary data Do3 output from the third comparison processing unit 22. A predetermined logical operation (specifically, differential processing) is performed between the two.

  The second binary calculation processing unit 27 treats the first binary data Do1 output from the first comparison processing unit 21 as the first bitmap data BM1, and from the first binary calculation processing unit 26. The output logical operation result is handled as the second bitmap data BM2, and a predetermined logical operation (specifically, differential processing) is performed between them.

  The logical operation result is once held in the binary data storage unit 30 as a binarized recording signal Dout, and then used for image recording processing in the marking engine unit 44 of the image recording unit 40. In other words, the marking engine unit 74 is a binarized recording signal that is binarized data that makes some of the dots inside the outline dot generated by the second binary arithmetic processing unit 27 virtually non-output dots. It functions as a recording energy control unit that performs image recording based on Dout.

<Halftone Processing Procedure; First Embodiment>
5 and 6 are diagrams for explaining binarization processing (specifically, halftone processing) in the binarization processing unit 20 of the first embodiment. In the case where the binarization processing unit 20 forms non-output dots with a dot-like halftone dot (dot screen) as a processing target, the gap profile storage unit 29b stores the gap shown in FIG. The description will be made assuming that the gap size profile data of the variable size system is stored.

  Here, FIG. 5 is a flowchart showing an outline of a halftone dot processing procedure by the binarization processing unit 20 of the first embodiment. FIG. 6 is a diagram illustrating a ring halftone dot generation process by halftone dot processing by the binarization processing unit 20 of the first embodiment. For example, FIG. 6A is an example of the first binary data Do1 output from the first comparison processing unit 21, that is, the first bitmap data BM1. FIG. 6B is an example of the second binary data Do2 output from the second comparison processing unit 22. FIG. 6C is an example of the third binary data Do3 output from the third comparison processing unit 23. FIG. 6D is an example of the second bitmap data BM2 output from the first binary calculation processing unit 26. FIG. 6E is an example of the binarized recording signal Dout output from the second binary calculation processing unit 27.

  In the binarization processing unit 20 of the first embodiment, when the multi-value image data DMV having density gradation is reproduced in a pseudo manner by the size of the colored dots called halftone dots, the input density is low The first feature is that the amount of the coloring material is reduced by forming voids inside the halftone dots when the concentration range is within the range of giving the void formation start point on the high concentration side.

  Further, as a technique for reducing the amount of the coloring material inside the halftone dot, a method for thinning out information inside the halftone dot on the binarized recording signal Dout, that is, when forming a void in the halftone dot, a normal halftone dot is formed. The second feature is that a point image and an image representing an air gap are first generated, and a method of logically synthesizing these two images is adopted.

  In addition, when reducing the amount of colorant by forming a gap in the center of the dot in the density range specified by generating two images, each dot size and gap size for each density was recorded. A third feature is that a halftone dot having a halftone dot size and a void size according to the profile is generated with reference to the profile data.

  The first comparison processing unit 21, which is the first halftone processing unit, responds to the density of the multivalued input image information (multivalued image data DMV) as in the conventional halftone dot growth up to the transition point density Ccnt. The first threshold value matrix MTX1 is set so as to output a halftone dot pattern having a size, and is compared with the multi-value image data DMV. Thereby, the first bitmap data BM1 shown in FIG. 6A is generated (S10).

  The second comparison processing unit 22 calculates the first binary data Do1 (= first) from the density (first density) C3 at which the multi-value image data DMV provides the low-density side void formation start point to the transition point density Ccnt. The dot of the second binary data Do2 grows in such a pattern as to follow the inside of the dot of the 1-bit map data BM1), and the second binary data Do2 after the transition point density Ccnt has the transition point density Ccnt. The second threshold value matrix MTX2 is set so as to maintain the state, and is compared with the multi-value image data DMV. Thereby, the second binary data Do2 shown in FIG. 6B is generated.

  When the multi-value image data DMV exceeds the density (transition point density) Ccnt that gives the maximum value of the number of voids, the third comparison processing unit 23 fills the inside of the dots of the second binary data Do2 from the outside to the inside. A third threshold value matrix MTX3 is set so that dots grow in such a pattern, and compared with the multi-value image data DMV. Thereby, the third binary data Do3 shown in FIG. 6C is generated.

  The first binary calculation processing unit 26 includes the second binary data Do2 output from the second comparison processing unit 22, and the third binary data Do3 output from the third comparison processing unit 22. The second bit map data BM2 shown in FIG. 6D is generated by performing a binary logic operation (logical subtraction process) of “Do2-Do3”.

  A series of processing by the second halftone dot processing unit configured by the second comparison processing unit 22, the third comparison processing unit 23, and the first binary calculation processing unit 26 is performed in an intermediate density range. When forming a void in a halftone dot when it is in C3 to C4, this is for forming a void in the halftone dot according to the void size variable method (in this example) or the void size fixing method. Enter the void size. This is processing for corresponding to the density of the image. The following is a summary from the viewpoint of the processing purpose.

  For example, according to the gap size variable method, when the multi-value input image information (multi-value image data DMV) is less than the first density C3, all the outputs of the second bitmap data BM2 are turned off (0; zero → white dot / none Output dots) (S20-NO, S30), and dots are turned on according to the density value exceeding the first density C3 (1 → black dot / output dot) until the density is higher than the first density C3 and lower than the transition point density Ccnt. The second bitmap data BM2 is generated (S20-YES, S22-NO, S32).

  When the signal of the first bitmap data BM1 is all on (1 → black dot / output dot) and above the transition point density Ccnt and below the second density C4, the density value exceeding the transition point density Ccnt is used. The second bitmap data BM2 is turned on (1 → black dot / output dot) in turn (0; zero → white dot / no output dot) in order (S22-YES, S24-NO, S34). Further, when the multi-value input image information (multi-value image data DMV) exceeds the second density C4, all the outputs of the second bitmap data BM2 are turned off (0; zero → white dot / no output dot) ( S24-YES, S36).

  In this way, as the second bitmap data BM2 that is the output result of the second halftone image generation unit, as shown in FIG. 6D, the intermediate density region of the density value of the multivalued image data DMV is used. In a certain range (C3 to C4), the black dots gradually increase, and after reaching the maximum value at the transition point density Ccnt, a halftone image is generated so that the black dots gradually decrease. That is, the halftone dot corresponding to the void (no output dot) can be dynamically changed according to the density (the processing result in the second binary calculation processing unit 27).

  That is, in the second halftone dot processing unit configured by the second comparison processing unit 22, the third comparison processing unit 23, and the first binary calculation processing unit 26, the second density exceeds the first density C3 and is second. The second bit is used as binary data representing non-output dots represented by a set of a plurality of output dots dynamically corresponding to the intensity (corresponding to the density of the input image) of the multi-value image data DMV up to the density C4. Map data BM2 is generated.

  In particular, in this example, since the gap is formed in the halftone dot only in the intermediate density region while adopting the gap size variable method, no output is made at the transition point density Ccnt in which the first bitmap data BM1 is all “1”. No output is achieved by maximizing the number of dots and by gradually reducing the number of non-output dots from the maximum value before and after the transition point density Ccnt (exceeding C3 to Ccnt and exceeding Ccnt to C4). The number of dots is dynamically associated with the input image density.

  Thereafter, the second binary calculation processing unit 27 outputs the first bitmap data BM1 (= first binary data Do1) output from the first comparison processing unit 21 and the first binary calculation processing. By performing a binary logical operation (logical subtraction process) of “BM1-BM2 = Do1- (Do2-Do3)” with the second bitmap data BM2 output from the unit 26, FIG. 2 is generated (S38).

  As shown in FIG. 6E, the binarized recording signal Dout output from the second binary calculation processing unit 27 becomes binary data having a void inside the halftone dot in the intermediate density region. In other words, the binarization processing unit 20 sets some dots inside the outer dots as non-output dots on the binarized recording signal Dout which is electronic data representing halftone dots.

  In this example, the gap size variable method is adopted, and the gap size is maximized at the approximate center of the intermediate density range, and the gap size is gradually reduced in the density range before and after that. It can be seen that the profile shown in FIG.

  Although not shown in the figure, in the case of following the gap size fixing method, there is no determination processing regarding the transition point density Ccnt in the gap size variable method and processing according to the determination result, and multi-value input image information (multi-value image When the data DMV) is less than the first density C1, the output of the second bitmap data BM2 is all off (0; zero → white dot). When the data DMV is greater than the first density C1 and less than the second density C2, the gap size b is set. Second bitmap data BM2 is generated that turns on a corresponding number of dots (1 → black dots). Further, when the multi-value input image information (multi-value image data DMV) exceeds the second density C2, the output of the second bitmap data BM2 is all turned off (0; zero → white dot).

  According to the halftone processing procedure by the binarization processing unit 20 of the first embodiment, the binarized recording signal Dout having a gap inside the halftone dot is reliably generated without destroying the outline shape of the halftone dot. In the output image, the colorant inside the halftone dot can be eliminated or the layer thickness can be reduced due to the gap in the data inside the halftone dot. Thereby, the transferability of the coloring material can be improved, and the image quality can be improved. Moreover, since the ratio of the coloring material amount which contributes to light absorption can be increased, the consumption amount of the coloring material can also be reduced.

  That is, since the void is formed inside the halftone dot without breaking the outline shape of the halftone dot, the colorant layer of the halftone dot can be made thin while preventing image quality deterioration. For example, since the dots are not thinned out at the halftone dot ends, there is no possibility that the reproduced halftone dots will be destroyed, and there will be no problem of image noise due to voids.

  Also, when adjusting the number of pixels to be thinned out inside the halftone dot, that is, by adjusting the number of voids in the halftone dot, when thinning the coloring material of the halftone dot, Since voids are not formed at the halftone dot end, there is no adverse effect of reducing the size of the halftone dot, and the halftone dot can be thinned uniformly.

  Further, since the amount of the coloring material inside the halftone dot is reduced when the input density exceeds the first density, as shown in the first stage of FIG. 6 (E), accumulation (clustering) is performed. With respect to a minute halftone dot, it is possible not to thin out the dot inside, so that the colored pixel area does not become too small and the dot reproduction of the halftone dot portion does not become unstable. That is, toner consumption can be reduced while maintaining highlight reproducibility. In particular, when a gap size variable method that optimizes the gap size for each density is adopted, it is possible to maintain the image quality and improve the toner consumption reduction effect while suppressing the generation of the pseudo contour at the gap generation position.

  Also, two images, a normal halftone dot image and an image representing voids, are generated first, and the two images are logically synthesized to form voids in the halftone dots, thereby reducing the amount of colorant inside the halftone dots. Thus, there is an advantage that the void can be formed in the halftone dot relatively easily by digital signal processing.

  Further, profile data (that is, threshold data) that defines the gap size corresponding to the density of the input image is stored in the gap profile storage unit 29b, and the threshold data and the multi-value image data DMV are compared to generate a gap. Therefore, by changing the profile in one processing device, it is possible to easily generate a halftone dot image having gaps with different characteristics, and binarization even if the gap size or gap generation density is changed. There is no need to redesign the processing parameters. Therefore, it is possible to efficiently design the parameter for generating the gap.

<Example of dot output of the first embodiment>
FIG. 7 is a diagram showing an example of halftone dot output when image recording processing is performed by the halftone dot processing procedure by the binarization processing unit 20 of the first embodiment described above. This example shows a design example of a ring halftone dot having a structure of 190 lines / 18 degrees. FIG. 7A shows the first bitmap data BM1 (from the first comparison processing unit 21). = Output example of first binary data Do1). FIG. 7B is an output example of the second binary data Do2 output from the second comparison processing unit 22. FIG. 7C is an output example of the binarized recording signal Dout output from the second binary calculation processing unit 27 in the multi-value image data DMV corresponding to FIGS. 7A and 7B. FIG. 7D shows an output example of the binarized recording signal Dout when the multi-value image data DMV has a higher density.

  FIG. 8 is a diagram showing a comparison between a conventional halftone dot and an electronic image of a halftone dot generated by the processing procedure by the binarization processing unit 20 of the first embodiment described above. This example also shows an example of a ring-shaped halftone dot having a structure of 190 lines / 18 degrees. Here, the upper part of the figure shows the state of halftone dot growth according to the prior art, the middle part shows the state of halftone dot growth by the binarization processing unit 20 of the first embodiment, and the lower part shows the binary value of the first embodiment. The state after the fixing of the toner image in which the image recording process is performed by the image recording unit 40 based on the binarized recording signal Dout at the time of 25% density input by the conversion processing unit 20 is shown.

  As can be seen from the comparison between the middle stage and the lower stage, when the halftone processing is performed in the binarization processing unit 20 of the first embodiment, the colorant layer inside the halftone dot without destroying the outline shape of the halftone dot by toner or ink. By performing binary calculation processing so as to reduce the thickness, even in the case of a ring-shaped halftone dot having a gap inside the halftone dot on the electronic image, that is, on the binarized recording signal Dout, A buried halftone dot image can be obtained. This means that if the halftone processing of the first embodiment is applied, the toner amount of the halftone image can be reduced.

<Overall Configuration of Image Forming Apparatus; Second Embodiment>
FIG. 9 is a diagram illustrating an overall outline of a second embodiment of the image forming apparatus shown paying attention to a portion related to binarization processing in a printing apparatus such as an electrophotographic system or an inkjet system. The second embodiment is based on the first bitmap data BM1 and the second bitmap data BM2 generated by the binarization processing unit 20 as a technique for reducing the amount of the coloring material inside the halftone dot. Thus, a characteristic is that a recording energy of a non-output dot inside the halftone dot is modulated so that the coloring material is lowered.

  In other words, the first embodiment is a purely electronic process in which some of the dots inside the outer dots are made non-output dots on the binarized recording signal Dout which is electronic data representing halftone dots. The second embodiment is different in that the recording energy control in the image recording unit 70 is also used.

  Specifically, as illustrated, the image forming apparatus 1 according to the second embodiment includes a color separation signal generation unit 10, a binarization processing unit 60, a binary data storage unit 30, and an image recording unit 70. It has.

  Although not shown, the binarization processing unit 60 of the second embodiment has a configuration in which the second binary calculation processing unit 27 in the binarization processing unit 20 of the first embodiment is removed.

  The image recording unit 70 includes a modulation control unit 72 that generates output modulation data DEX for recording, and a marking engine unit 74 that performs image recording processing based on the output modulation data DEX generated by the modulation control unit 72. ing.

  The binarization processing unit 60 modulates the first bitmap data BM1 (= first binary data Do1) output from the first comparison processing unit 21 via the binary data storage unit 30, respectively. 72, and the second bitmap data BM2 output from the first binary calculation processing unit 26 is supplied to the modulation control terminal 72b of the modulation control unit 72, respectively.

  The modulation control unit 72 generates output modulation data DEX by using the first bitmap data BM1 as an exposure on / off control signal and the second bitmap data BM2 as output modulation control data.

  In the image recording unit 70 having such a configuration, the marking engine unit 74 controls the recording energy of halftone dots based on the output modulation data DEX so that the coloring material inside the halftone dots is reduced. That is, the marking engine unit 74 functions as a recording energy control unit that performs image recording based on the output modulation data DEX generated by the modulation control unit 72.

  For example, if the marking engine unit 74 is of an electrophotographic system, the exposure energy is controlled using the output modulation data DEX as exposure modulation data so that the colorant inside the halftone dot is reduced. Further, when the marking engine unit 74 is of an ink jet type, the output amount data DEX is used as the ink amount modulation data, and the ink amount is controlled so that the colorant inside the halftone dot is lowered.

<Halftone Processing Procedure; Second Embodiment>
10 and 11 are diagrams for explaining binarization processing (specifically halftone processing) in the image forming apparatus 1 of the second embodiment. The marking engine unit 74 is shown as an electrophotographic type. Further, a case will be described where the binarization processing unit 20 forms non-output dots with a dot-like halftone dot (dot screen) as a processing target.

  Here, FIG. 10 is a flowchart showing an outline of a halftone dot processing procedure by the image forming apparatus 1 of the second embodiment. FIG. 11 is a diagram illustrating a ring halftone dot generation process by halftone dot processing by the image forming apparatus 1 according to the second embodiment. For example, FIG. 11A is an example of the first binary data Do1 output from the first comparison processing unit 21, that is, the first bitmap data BM1. FIG. 11B is an example of the second binary data Do2 output from the second comparison processing unit 22. FIG. 11C is an example of third binary data Do3 output from the third comparison processing unit 23. FIG. 11D is an example of the second bitmap data BM2 output from the first binary arithmetic processing unit 26. Each is the same as FIG. 6 (A) to FIG. 6 (D).

  As in the first embodiment, the first comparison processing unit 21 serving as the first halftone processing unit has halftone dots having a size corresponding to the density of the multivalued input image information (multivalued image data DMV). The first bitmap data BM1 forming is generated (S10). The first comparison processing unit 21 supplies the generated first bitmap data BM1 to the on / off control input terminal 72a of the modulation control unit 72 (S42).

  In the second halftone dot processing unit composed of the second comparison processing unit 22, the third comparison processing unit 23, and the first binary calculation processing unit 26, the same procedure as in the first embodiment is performed. Accordingly, the second bitmap data BM2 for forming halftone dots corresponding to the gaps having a size corresponding to the density of the multi-value input image information (multi-value image data DMV) is generated (S20 to S36). Then, the second halftone dot processing unit supplies the generated second bitmap data BM2 to the modulation control terminal 72b of the modulation control unit 72 (S44).

  The modulation control unit 72 generates output modulation data DEX using the first bitmap data BM1 as an exposure on / off control signal and the second bitmap data BM2 as output modulation control data (S46).

  Here, in the configuration according to the second embodiment, when the image recording unit 70 uses a method of forming a toner image on a portion exposed with light, the first bitmap data BM1 (= on / off control signal) is turned on. Exposure is performed at the time of (a hatched dot portion in FIG. 11A).

  At this time, when the second bitmap data BM2 (= output modulation data) is “0; zero (white dot portion in FIG. 11D)”, the exposure is 100%, and the second bitmap data BM2 (= output modulation data). ) Is “1 (hatched dot portion in FIG. 11D)”, exposure is performed with a small amount of light (for example, 50% or less).

  By doing so, the dots whose second bitmap data BM2 (= output modulation data) is “1” can be made substantially non-output dots. Note that the true no-output dots of the first embodiment and the substantially no-output dots of the second embodiment are collectively referred to as virtual no-output dots.

  The second bitmap data BM2 (= output modulation data) is obtained by a process similar to the process in the first embodiment, and is obtained only when the first bitmap data BM1 (= on / off control signal) is on. If exposure is performed, as a result, a print pattern having voids inside the halftone dots in the intermediate density region as shown in FIG. 6E is obtained.

  Therefore, substantially the same halftone dot output image as in the first embodiment can be obtained, and by reducing the exposure amount inside the halftone image, the colorant inside the halftone dot is reduced in the output image. It can be eliminated or the layer thickness can be reduced. Thereby, the transferability of the coloring material can be improved, and the image quality can be improved. Moreover, since the ratio of the coloring material amount which contributes to light absorption can be increased, the consumption amount of the coloring material can also be reduced.

  In the first embodiment, a normal halftone dot image and an image representing a gap are first generated, and a gap is formed in the halftone dot by logically synthesizing these two images. Although there is an advantage that the void can be formed in the halftone dot relatively easily by the processing, the void concentration on the electronic data (binarized recording signal Dout) becomes “0; zero”, and the void concentration can be freely adjusted. Basically I can't do that. Therefore, when the coloring material in the halftone dots is thinned, it is necessary to adjust the number of pixels to be thinned out inside the halftone dots in order to adjust the degree of thinning.

  On the other hand, in the second embodiment, exposure is performed by adjusting the amount of light when the second bitmap data BM2 (= output modulation data) is “1 (hatched dot portion in FIG. 11D)”. Therefore, although the modulation control unit 72 is required, there is an advantage that the gap density can be freely adjusted. When thinning the colorant in the halftone dots, the degree of thinning can be adjusted while keeping the same number of pixels thinned out inside the halftone dots.

<Halftone Processing Procedure; Third Embodiment; Basic>
FIG. 13 and FIG. 14 are diagrams for explaining the binarization processing (specifically halftone processing) of the third embodiment. In the binarization processing of the third embodiment, the binarization processing unit 20 forms a non-output dot according to a predetermined rule, with the original halftone dot structure being a linear halftone dot (line screen). It has the characteristic in the point to do.

  Here, FIG. 13 is a diagram for explaining linear halftone dots, and FIG. 14 is a diagram for explaining a process of forming non-output dots (voids) with respect to the linear halftone dots. (A)-(E) respond | correspond to FIG. 6 (A)-(E), respectively.

  In the process of forming the linear halftone dots, the input multi-valued data to be processed (see FIG. 13A) and the threshold matrix for the linear halftone dots (see FIG. 13B) are converted into FIG. As shown in C), the binarized recording signal Dout is generated by comparing with a comparator. In this case, as shown in FIG. 13D, the dot shape is not a line shape (line shape) at a low concentration (for example, 8), but as shown in FIG. When it gets higher, dots grow in one direction and connect in a line.

  That is, as shown in an example of a line screen of 190 lines / 72 degrees in FIG. 13F, in the line-shaped screen processing, isolated dots are generated in a low density region, and dots are grown in one direction therefrom. It is combined with adjacent dots at a low density to form a line.

  Here, as shown in FIG. 14, the binarization processing unit 20 follows the flowchart shown in FIG. 5 showing an example of the processing procedure in the same manner as in the first embodiment handling the dot-shaped halftone dots described above. When the intensity of the image signal is in a predetermined range that exceeds a predetermined value, the outline dot, which is an output dot that contributes to the outline formation of such a line-shaped halftone dot, is maintained as the output dot, that is, the line shape is maintained. On the other hand, the signal inside the halftone dot (in this case, meaning the inside of the line) can be thinned out by the synthesis process of the binary data in which some of the dots inside the outline dot are effectively non-output dots.

  By applying the present invention to a linear halftone dot (line screen), the same advantage as the first embodiment can be obtained while enjoying the advantages of the linear halftone dot that is resistant to disturbances during image formation and color moire. The effect can be enjoyed, and the layer thickness of the coloring material inside the halftone dot can be reduced without destroying the outline shape of the halftone dot by toner or ink. The colorant at the halftone dot can be effectively thinned without causing deterioration in image quality, and the consumption of the colorant can be reduced.

<Example of halftone dot output of third embodiment>
FIG. 15 is a diagram illustrating a first example of gap formation for linear halftone dots by the halftone dot processing procedure of the third embodiment. This first example shows an application example for a 190-line / 72-degree line screen. FIG. 15A shows the multivalued image data DMV, and FIG. 15B shows the binarized image of the line screen structure. The first example, FIG. 15C, shows a first example of gap generation for the line screen. Respectively, the density values are 12.5%, 25%, 50%, 75%, and 100%.

  Depending on the parameters shown in FIGS. 14B, 14C, and 14D, voids are scattered in the line structure on the low density side (12.5% to 25% in this example) of the multi-valued image data DMV. However, in the predetermined density range of the multi-valued image data DMV (in this example, 50% to 75%), no output dots (voids) are linearly connected within the linear halftone dot. In other words, voids can grow in the linear structure to form a double line structure (particularly referred to as a complete hollow double line structure).

  However, in this case, since the gap is narrowed on the high density side (for example, remarkable at 75%), depending on the number of screen lines, when the image is actually output using toner, the gap is crushed, and the reproducibility of gradation is high. It can be a problem. In other words, when a line-shaped air gap is provided in the line structure, if the number of screen lines increases, a completely hollow double line structure will cause the line structure to become too thin, resulting in a marking process. It may happen that the reproducibility of the image deteriorates.

<Second Halftone Output Example of Third Embodiment>
FIG. 16 is a diagram illustrating a second example of forming a gap with respect to a linear halftone dot by the halftone dot processing procedure according to the third embodiment. This second example also shows an application example for a line screen of 190 lines / 72 degrees, and FIGS. 16A to 16C correspond to FIGS. 15A to 15C, respectively.

  By changing the parameters shown in FIGS. 14B, 14C, and 14D, the image example of the second example can be applied, unlike the image example of the first example. Even in the second example, on the low density side of the multi-value image data DMV (12.5% to 25% in this example), voids are scattered in the line structure, but the density becomes higher, and the multi-value image data DMV. In the predetermined density range (in this example, 50% to 75%), the non-output dots are kept isolated in the linear halftone dots, that is, the non-output dots are kept in the linear halftone dots. It is possible not to be connected in a line.

  In this case, unlike the first example, non-output dots (voids) of a certain size can be reliably formed even on the high density side, so even if the number of screen lines increases, linear halftone dots By preventing the non-output dots from being isolated in the linear halftone dots so that the voids are not connected in a linear manner, the phenomenon that the voids become narrow on the high density side can be prevented. As a result, even when an image is actually output using toner, it is possible to prevent the phenomenon that the gaps are crushed and the reproducibility of the line structure is more stable, so that the reproducibility of gradation can be kept good.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above-described embodiment without departing from the gist of the invention, and embodiments to which such changes or improvements are added are also included in the technical scope of the present invention.

  Further, the above embodiments do not limit the invention according to the claims (claims), and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. Absent. The embodiments described above include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. Even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, as long as an effect is obtained, a configuration from which these some constituent requirements are deleted can be extracted as an invention.

  For example, in the first and second embodiments, when generating the image representing the gap shown in FIG. 6D, the second threshold value matrix MTX2 that mainly defines the gap size on the low density side and the high density side The third threshold value matrix MTX3 for defining the gap size is prepared and the gap size in the entire intermediate density region of the multi-value image data DMV is defined by combining them. A gap threshold value matrix (for example, two threshold values on the low density side and the high density side are entered in one coordinate) that gives the halftone dot pattern of FIG. 6 (D) that defines the gap size in the entire intermediate density range. Alternatively, the binarization processing may be performed by the first binary calculation processing unit 26 using this gap threshold value matrix. With such a configuration, the number of threshold matrixes to be used can be reduced.

  In the first embodiment, the normal halftone dot image shown in FIG. 6 (A) and the halftone dot image shown in FIG. 6 (D) are first generated, and the two images are logically synthesized. As a result, voids were formed in the halftone dots, but binarization processing was performed after converting the threshold value or input image density so as to obtain a halftone dot image having voids as shown in FIG. You may do it.

  With such a configuration, a halftone image (binary image) corresponding to a basic halftone image (an example of a binary image) and a void image (an example of a binary image) for forming a void in the halftone dot. A plurality of binarization processing units that generate an example of an image (corresponding to FIG. 6D) and a function unit that synthesizes these two binary images can be omitted, and a halftone image having a gap can be efficiently created. Can be generated.

<Regarding the configuration using an electronic computer>
Further, the above-described mechanism for performing halftone dot processing is not limited to being configured by a hardware processing circuit, but can also be realized by software using an electronic computer (computer) based on a program code that realizes the function. It is.

  Accordingly, the present invention provides a program suitable for realizing the image processing method, the image processing apparatus or the image forming apparatus according to the present invention by software using an electronic computer (computer) or a computer-readable storage medium storing the program. Can also be extracted. By adopting a mechanism that is executed by software, it is possible to enjoy the advantage that the processing procedure and the like can be easily changed without changing hardware.

  When a computer performs a series of halftone dot processing by software, a computer (such as an embedded microcomputer) in which a program constituting the software is incorporated in dedicated hardware or a CPU (Central Processing Unit) System on a chip (SOC) that implements a desired system by mounting functions such as logic circuits and storage devices on a single chip, or various functions by installing various programs It is installed from a recording medium in a general-purpose personal computer that can be executed.

  The recording medium causes a change state of energy such as magnetism, light, electricity, etc. to the reading device provided in the hardware resource of the computer according to the description content of the program, and in the form of a signal corresponding thereto. The program description can be transmitted to the reader.

  For example, a magnetic disk (including a flexible disk FD), an optical disk (CD-ROM (Compact Disc-Read Only Memory)), a DVD on which a program is recorded, which is distributed to provide a program to a user separately from a computer. (Including Digital Versatile Disc), magneto-optical disc (including MD (Mini Disc)), or package media (portable storage media) made of semiconductor memory, etc. It may be configured by a ROM, a hard disk, or the like in which a program is recorded, which is provided to the user in a state of being recorded. Or the program which comprises software may be provided via communication networks, such as a wire communication or radio | wireless.

  For example, a storage medium storing software program codes for realizing a halftone processing function is supplied to a system or apparatus, and a computer (or CPU or MPU) of the system or apparatus reads out the program codes stored in the storage medium By executing this, the same effect as in the case of the hardware processing circuit is achieved. In this case, the program code itself read from the storage medium realizes a halftone processing function.

  Further, not only the function of performing halftone dot processing is realized by executing the program code read out by the computer, but also an OS (Operating Systems; basic software) running on the computer based on the instruction of the program code May perform a part or all of the actual processing, and a function of performing halftone dot processing by the processing may be realized.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. The CPU or the like provided in the card or the function expansion unit may perform a part or all of the actual processing, and a function of performing halftone processing by the processing may be realized.

  The program is provided as a file describing a program code that realizes the function of performing halftone dot processing. In this case, the program is not limited to being provided as a batch program file, and the hardware of the system configured by a computer Depending on the configuration, it may be provided as an individual program module.

1 is a diagram illustrating an overall outline of an image forming apparatus according to a first embodiment. It is a figure which shows the structure of the binarization process part of 1st Embodiment. It is a figure which shows an example of the space | gap size profile which shows the characteristic of the threshold value data for space | gap formation. FIG. 4 is a diagram illustrating an example of an image (A) generated by normal binarization processing and images (B) and (C) generated using the gap size profile shown in FIG. 3 in the processing of the present embodiment. is there. It is a flowchart which shows the outline | summary of the halftone process procedure by the binarization process part of 1st Embodiment. It is a figure which shows the production | generation process of the ring-shaped halftone dot by the halftone dot process of 1st Embodiment. It is a figure which shows the example of an output of a halftone dot when performing an image recording process by the halftone dot process procedure by the binarization process part of 1st Embodiment. It is the figure which showed the comparison with the electronic image of the halftone dot produced | generated by the process sequence of 1st Embodiment and the halftone dot of the conventional method. It is a figure which shows the whole image forming apparatus outline | summary of 2nd Embodiment. 10 is a flowchart illustrating an outline of a halftone processing procedure performed by the image forming apparatus according to the second embodiment. It is a figure which shows the production | generation process of the ring-shaped halftone dot by the halftone dot process of 2nd Embodiment. It is a figure explaining the conventional general halftone processing and a halftone image. It is a figure explaining a linear halftone dot (line screen). It is a figure explaining the process in which a non-output dot (gap) is formed with respect to a linear halftone dot. It is a figure which shows the 1st example of the space | gap formation with respect to the linear halftone dot by the halftone dot process procedure of 3rd Embodiment. It is a figure which shows the 2nd example of the space | gap formation with respect to the linear halftone dot by the halftone dot process procedure of 3rd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Color separation signal generation part, 20, 60 ... Binarization processing part, 21, 22, 23 ... Comparison processing part, 26, 27 ... Binary calculation processing part, 28 ... Gap formation processing part , 29 ... threshold matrix storage unit, 29 a ... halftone dot profile storage unit, 29 b ... gap profile storage unit, 30 ... binary data storage unit, 40, 70 ... image recording unit, 44, 74 ... marking engine unit, 50 ... profile Switching command unit, 72 ... modulation control unit

Claims (15)

A halftone dot represented by a set of one or a plurality of output dots corresponding to the intensity of the input image signal is formed, and the halftone dot is formed so that the amount of colorant in the halftone dot portion is reduced. An image processing method for generating a halftone image in a pseudo manner by setting a part of dots to a virtually non-output dot,
When the intensity of the image signal exceeds the first value indicating the first density and is equal to or lower than the second value indicating the second density higher than the first density , it contributes to the outline formation of the halftone dots. When the outer dots, which are output dots to be output, are maintained as the output dots, some of the dots inside the outer dots are set to the virtually no output dots, and the intensity of the image signal is equal to or lower than the first value In addition, while maintaining the outline dots, which are output dots that contribute to the outline formation of the halftone dots, as the output dots, some of the dots inside the outline dots are not made to be the virtually no output dots. Image processing method. A halftone dot represented by a set of one or a plurality of output dots corresponding to the intensity of the input image signal is formed, and the halftone dot is formed so that the amount of colorant in the halftone dot portion is reduced. An image processing apparatus that generates a halftone image in a pseudo manner by setting a part of dots to a virtually non-output dot,
When the intensity of the image signal exceeds the first value indicating the first density and is equal to or lower than the second value indicating the second density higher than the first density , it contributes to the outline formation of the halftone dots. When the outer dots, which are output dots to be output, are maintained as the output dots, some of the dots inside the outer dots are set to the virtually no output dots, and the intensity of the image signal is equal to or lower than the first value In addition, binarization processing that keeps the outline dots, which are output dots that contribute to the outline formation of the halftone dots, as the output dots, but does not make some of the dots inside the outline dots to be the virtually non-output dots An image processing apparatus comprising a unit. The binarization processing unit
A first halftone dot image generation unit for generating binary data representing the halftone dots represented by a set of a plurality of output dots corresponding to the intensity of the input image signal;
A second halftone image generation unit that generates binarized data representing a set of true no-output dots when the intensity of the image signal exceeds the first value and is equal to or less than the second value ;
Binary data representing the halftone dot generated by the first halftone dot image generation unit and binarization representing a set of the true non-output dots generated by the second halftone dot image generation unit The image processing according to claim 2, further comprising: an arithmetic processing unit that generates binarized data in which a part of the dots inside the outer dots are converted into the virtually non-output dots by performing differential processing on the data. apparatus. The second halftone dot image generation unit is configured so that the number of true no-output dots gradually decreases from the maximum value before and after the intensity of the transition point at which the number of true no-output dots becomes maximum. The image processing apparatus according to claim 3, wherein the number of true non-output dots dynamically corresponds to the intensity of the image signal. The second halftone dot image generation unit is configured to change the intensity of the transition point at which the number of true no-output dots is maximum when the intensity of the input image signal is shifted from the low intensity side. 5. The image processing apparatus according to claim 4, wherein all of the binarized data representing the halftone dots generated by one halftone dot image generation unit is a value that becomes the output dot. The second halftone image generation unit generates binarized data representing a certain number of true non-output dots when the intensity of the image signal exceeds the first value. Item 4. The image processing apparatus according to Item 3. The second halftone image generator generates binary data representing the fixed number of true non-output dots in a range of the intensity of the image signal from the first value to the second value. The image processing device according to claim 6, wherein the image processing device is generated. The image processing apparatus according to claim 2, wherein the binarization processing unit collects a plurality of the non-output dots in a lump. The image processing apparatus according to any one of claims 2 to 8, wherein the binarization processing unit sets a dot-like halftone dot as a processing target. The binarization processing unit is configured to process a linear halftone dot having a structure in which the halftone dots are linearly connected in a region where the input image signal is equal to or higher than a predetermined density. The image processing apparatus according to claim 1. In the binarization processing unit, when a part of the dots inside the outline dot of the linear halftone dot is changed to the virtual non-output dot, the non-output dot is in the linear form in a predetermined density range. The image processing apparatus according to claim 10, wherein the image processing apparatus is arranged in a line within a halftone dot. In the binarization processing unit, when some of the dots inside the outline dot of the linear halftone dot are changed to the virtual non-output dot, the non-output dot is isolated in the linear halftone dot. The image processing apparatus according to claim 10, wherein the state is maintained. A halftone dot represented by a set of one or a plurality of output dots corresponding to the intensity of the input image signal is formed, and the halftone dot is formed so that the amount of colorant in the halftone dot portion is reduced. An image forming apparatus that forms a pseudo halftone image by making the dots of the part a virtually non-output dot,
An outline forming the outline of the halftone dot when the intensity of the image signal exceeds a first value indicating a first density and is equal to or less than a second value indicating a second density higher than the first density. While maintaining a dot as the output dot, a part of the dots inside the outline dot is set to the virtually no output dot, and when the intensity of the image signal is equal to or less than the first value , A binarization processing unit that maintains the outer dots, which are output dots that contribute to the outer contour formation, in the output dots, and does not make some of the dots inside the outer dots into the virtually no output dots;
An image recording unit that forms the halftone image having the virtual non-output dots in the halftone dots based on the binarized data generated by the binarization processing unit. An image forming apparatus. The binarization processing unit
A first halftone dot image generation unit for generating binary data representing the halftone dots represented by a set of a plurality of output dots corresponding to the intensity of the input image signal;
A second halftone image generation unit that generates binarized data representing a set of true no-output dots when the intensity of the image signal exceeds the first value and is equal to or less than the second value ;
Binary data representing the halftone dot generated by the first halftone dot image generation unit and binarization representing a set of the true non-output dots generated by the second halftone dot image generation unit An arithmetic processing unit that generates binarized data by converting a part of the data into a non-output dot by performing differential processing on the data, and
The image recording unit includes a recording energy control unit that performs image recording based on binarized data in which some of the dots inside the outline dot generated by the arithmetic processing unit are non-output dots. The image forming apparatus according to claim 13. The binarization processing unit includes a first halftone dot image generation unit that generates binary data representing the halftone dot represented by a set of a plurality of output dots corresponding to the intensity of the input image signal. A second halftone image generating unit that generates binarized data representing a set of true non-output dots corresponding to the intensity of the image signal that exceeds the first value and is equal to or less than the second value. Have
The image recording unit uses the binarized data representing the halftone dot generated by the first halftone dot image generation unit as on / off control input, and is generated by the second halftone dot image generation unit. A modulation control unit that generates output modulation data using binarized data representing a set of true no-output dots as modulation control input, and recording energy for performing image recording based on the output modulation data generated by the modulation control unit The image forming apparatus according to claim 13, further comprising a control unit.