JP6740714B2 - Image processing apparatus, image processing method, and program - Google Patents

Description

The present invention relates to an image processing device, an image processing method, and a program.

Conventionally, the image stability of electrophotography is generally inferior to that of offset printing. Therefore, various techniques have been attempted to bring the image stability of electrophotography close to the image quality of offset printing. One of the differences between electrophotography and offset printing is the difference in gradation expression. An electronic photograph expresses gradation by performing image processing such as a line screen, a halftone screen, and an FM screen. The halftone screen outputs an image having gradation similar to that of offset printing as compared with other screens.

For example, Patent Document 1 cites the use of two types of screens in order to improve the image quality of intermediate gradations and the stability of image quality, which are poor at dot screens. That is, the use of two types of screens is a line screen up to the middle gradation and a white halftone dot (a screen in which dots are formed as if the halftone screen is reversed) for the high gradation.

However, in the above-described conventional techniques, no consideration is given to a method for improving the image quality and ensuring the stability of the image quality in the middle to high gradations in which the screen is switched. It is conceivable that a problem may occur in the image quality and stability in the. Further, it is necessary to store two screens and further perform a dot rearrangement process for each dot array in the adjacent portion of two different screens. For this reason, image processing is expected to take longer than in the case of using a conventional single screen, and there is a problem that the memory needs to have a larger capacity. As described above, the conventional halftone screen has a problem that the stability of the image quality in the middle gradation is not excellent.

The present invention has been made in view of the above, and an object of the present invention is to improve the image stability of a halftone image in a halftone screen.

In order to solve the above-mentioned problems and achieve the object, the present invention provides an image determination unit that determines a gradation value for each predetermined range of input image data, and a black and white image of a dot image having the gradation value. When the input area ratio indicating the ratio is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster, and the growth of the dot cluster is performed. screen distance of the dot Katamarikan is when it becomes less than a predetermined value, to form the smallest white dot image by connecting the dots mass adjacent to form a crosslinked portion in number of gradations adjacent in the process And a generation unit. In the present invention, the screen generation unit may contact the dot cluster in three or more directions out of eight directions around the dot image when arranging a new dot image in contact with the dot cluster. When the dot cluster formation unit that arranges a new dot image to form the dot cluster and the growth of the dot cluster by the dot cluster formation unit, and the distance between the adjacent dot clusters is equal to or less than a predetermined value , A blank image forming portion that forms a cross-linked portion with a minimum number of gradations to form a white halftone dot image by connecting with the adjacent dot clusters, and after the formation of the white halftone dot image is completed, A dot image forming unit that fills a white dot portion formed in the white dot image with a dot image.

INDUSTRIAL APPLICABILITY The present invention has an effect that it is possible to improve image stability in a halftone of a halftone screen image.

FIG. 1 is an explanatory diagram showing terms of screen images related to the present embodiment. FIG. 2A is an explanatory diagram illustrating an example of dot formation in the case of a halftone dot shape. FIG. 2-2 is an explanatory diagram showing an example of dot growth when shifting from a halftone dot shape to an open halftone dot shape. FIG. 2-3 is an explanatory diagram showing an example of dot growth in the outline halftone dot shape. FIG. 3 is a block diagram showing the system configuration of the image forming apparatus according to this embodiment. FIG. 4 is a block diagram showing a configuration including the function of the image processing unit. FIG. 5 is a block diagram showing the functional configuration of the screen generation unit. FIG. 6 is a flowchart showing an example of screen processing according to this embodiment. FIG. 7 is a graph showing image stability in the conventional halftone screen processing and the halftone screen processing of the present embodiment. FIG. 8 is an explanatory diagram showing a dot growth processing example according to the present embodiment. FIG. 9 is an explanatory diagram showing an example of a dot growth method until the inter-dot distance becomes 50 μm or less according to the present embodiment. FIG. 10 is an explanatory diagram showing an example of a dot growth method from a halftone dot shape to an open dot halftone dot shape. FIG. 11 is an explanatory diagram showing the relationship between the halftone dot shape and the screen angle. FIG. 12 is an explanatory diagram showing an example of the dot growth order in the bridging portion according to the present embodiment. FIG. 13 is an explanatory diagram showing a state immediately after the white halftone dot portions are formed by the different two-direction bridge portions according to the present embodiment. FIG. 14 is an explanatory diagram showing an example of the dot growth order of the white dot shape formed by the different two-direction bridging portions according to the present embodiment. FIG. 15 is an explanatory diagram showing an inappropriate example (NG example) in which the white halftone dot portions are formed so that the dot images are arranged linearly in the main scanning direction. FIG. 16 is an explanatory diagram showing a suitable example (OK example) in which the white dot portions are formed so that the dot images are arranged linearly in the main scanning direction. FIG. 17 is a graph showing the image stability in the conventional halftone screen processing and the halftone screen processing of the present embodiment. FIG. 18 is an explanatory diagram showing the relationship between the dot distance and the unstable toner adhesion area. FIG. 19 is an explanatory diagram showing a conventional halftone screen growth method. FIG. 20 is an explanatory diagram showing the inter-dot distance when the input area ratio is 50%.

An embodiment of an image processing device, an image processing method, and a program according to the present invention will be described in detail below with reference to the accompanying drawings.

(Embodiment)
[How to grow dots on a halftone screen]
<Bad dot screen defect>
First, a dot growth method for a halftone screen will be described. In the image formation using the electrophotographic method, when the distance between the dot clusters is short, the exposure distribution edges of the adjacent dot clusters overlap each other, so that a certain amount of exposure intensity is generated in the non-image area (background area). When the exposure intensity is generated in this manner, a minute latent image electric potential is generated which adheres the toner onto the photosensitive member immediately after charging.

In such a case, as shown in FIG. 18, the toner adheres to a position other than the position where the toner is applied, that is, the toner adheres to a position other than the position where the image is originally formed (non-adhesion region, background part). There is a phenomenon of doing. This phenomenon is more likely to appear as the distance between the dot clusters of the input image is shorter (see dl in FIG. 20 described later). Therefore, due to the instability peculiar to electrophotography, at a certain distance between the dot clusters, toner may or may not be attached to a place where toner should not be originally attached. As a result, the image quality is degraded.

First, a conventional halftone screen growth method will be described. The growth of the halftone screen is an image process in which the size of the dot image is changed to change the ratio of white and black so as to make the image look pseudo halftone (medium gradation). Hereinafter, the growth of a dot image or the formation of a dot image has the same meaning, and is appropriately described as “formation” or “growth”.

FIG. 19 is an explanatory diagram showing a conventional halftone screen growth method. On the halftone screen, as shown in FIG. 19, the dot image is written as the growth order (image density) of the dot image increases. The order of growth of dot images is such that the dot image that is closer to the dot image of one dot pixel called the growth center (corresponding to the dot formation center) in terms of distance is ranked from the dot image of the peripheral part. Be seen.

That is, in the conventional halftone screen growth method, as shown in FIG. 19, the gradation is expressed by forming a large dot image with the growth center of the dot image as a reference. Therefore, in the conventional halftone screen growth method, the distance between the dot clusters becomes smaller as the gradation becomes larger, and the toner adhesion becomes unstable. .. From the above, it is necessary to change the dot image growing method in order to improve the image stability of the halftone of the halftone screen.

In the conventional halftone screen growth method, the distance between dot clusters becomes small in any dot growth method, and there are gradations that deteriorate image stability. However, it is possible to give features in the order of dot growth. In the conventional halftone dot screen growth method, the image stability in the middle gradation is not excellent because many gradations, which are the inter-dot distances at which the image stability of the non-toner-attached portion deteriorates, are seen in the middle gradation. Here, as shown in FIG. 20, it has been confirmed that when the distance dl between the dot clusters becomes 50 μm or less, the above-mentioned deterioration of image quality frequently occurs.

As described above, in the halftone screen, since the distance between the dot clusters becomes small, the toner adhesion becomes unstable, and the image quality and the stability of the image quality are impaired. The phenomenon occurs when the distance d1 between the dot clusters is less than 50 μm and the input area ratio is around 50%.

<Outline example of halftone screen processing according to the embodiment>
Therefore, in order to solve the above-described problems of the halftone screen, the following halftone screen processing is performed to improve the image quality of the halftone screen and stabilize the image quality (see FIGS. 2-1 to 2-3). ). Hereinafter, a specific example will be described. In addition, in the drawings showing each image referred to in this specification, an image of one square=1 dot (pixel) is shown.

First, terms of screen images related to the present embodiment will be described with reference to FIG. In FIG. 1, reference numeral dc indicates the growth center of the dot image, and reference numeral db is a dot block formed so as to surround the growth center dc with the dot image. Reference numeral dk is a bridge portion that connects the dot cluster db to be processed and the adjacent dot cluster db with a bridge structure. The symbol ws is a white halftone dot portion surrounded by the bridge portion dk.

FIG. 2A is an explanatory diagram illustrating an example of dot formation in the case of a halftone dot shape. The dot image is grown (formed) by forming dot images around the growth center dc on the left of FIG. 2-1 and, as a result, forming dot clusters db as shown on the right of FIG. 2-1.

FIG. 2B is an explanatory diagram showing an example of dot growth processing when the halftone dot shape shown in FIG. Here, as shown in FIG. 2A, the dot cluster db for which the dot image growth processing is performed is connected to the dot cluster db by the bridge portion dk to form the white halftone dot portion ws.

FIG. 2-3 is an explanatory diagram showing an example of dot growth (formation) processing from the outline halftone dot shape shown in FIG. 2-2. Here, the dot image is formed so that the white dot portions ws processed in FIG. 2B are sequentially filled with the dot image, and as a result, the solid image is formed.

[System configuration example]
Next, a system configuration and an operation example thereof for realizing the halftone screen processing according to the above-described embodiment will be described.

FIG. 3 is a block diagram showing the system configuration of the image forming apparatus according to this embodiment. The image forming apparatus corresponds to, for example, a copying apparatus, a printing apparatus such as a laser printer, a facsimile apparatus, or a multifunction machine having at least one of a copying function, a printing function, and a facsimile function. Further, the image forming apparatus may be either a single color or a color obtained by superposing toners of Y (yellow), M (magenta), C (cyan) and K (black). The image forming apparatus includes an image processing unit 100, a CPU (Central Processing Unit) 110, a ROM (Read Only Memory) 111, a RAM (Random Access Memory) 112, and an image forming unit 120.

The image processing unit 100 is mounted on a controller board or the like of the image forming apparatus, performs predetermined image processing on input image data, and outputs the image data to the image forming unit 120. The image processing unit 100 is configured, for example, as shown in FIG. 4, which will be described later, and the CPU 110 executes predetermined control described later using the RAM 112 as a working memory in accordance with a control program stored in the ROM 111.

In the case of a laser printer, the image forming unit 120 has an optical writing unit including a laser optical system and a writing control unit, and according to an image signal sent from the image processing unit 100, laser modulation is performed and the surface of the photoconductor after charging is performed. To expose. By this exposure, a latent image of a dot image is formed on the photoreceptor after charging, and the desired image is formed on the recording paper through the processes of development, transfer, and fixing as is known in general electrophotographic apparatuses. It is formed.

FIG. 4 is a block diagram showing a configuration including the function of the image processing unit 100. The image processing unit 100 includes an image determination unit 101, a screen generation unit 102, a dither processing unit 103, a dither table 104, and a PMW unit 105.

The image determination unit 101 determines the gradation value for each predetermined range for the input image data. That is, the image determination unit 101 reads the image information (gradation value) of the halftone area (medium gradation area) from the input image data.

The screen generation unit 102 forms a dot image around each of the plurality of growth centers dc of the halftone dot screen in which the input area ratio indicating the black-and-white ratio of the gradation value dot image is smaller than the value at which an image defect appears, and forms dots. Form a lump db. Subsequently, the screen generation unit 102 forms the bridge portion dk with the minimum number of gradations when the distance between the adjacent dot clusters db becomes equal to or less than a predetermined value as the dot clusters db grow, and the adjacent dot clusters db are formed. By connecting with, a white halftone dot part ws is formed. A detailed concrete example of the screen generation unit 102 will be described later.

The dither processing unit 103 determines the dither to be applied from the input image information, reads the dither pattern data stored in the dither table 104, and executes the dither processing according to this dither pattern data. Note that the dither table 104 stores a plurality of different dither pattern data in a storage device such as an HDD (hard disk drive).

If the image forming unit 120 is a laser printer, the PMW unit 105 performs PMW (Pulse Width Modulation) based on the image data subjected to the dither processing by the dither processing unit 103. After that, the PMW unit 105 sends a signal for modulating and outputting the LD (laser diode) to an optical writing unit (not shown) of the image forming unit 120.

Note that some or all of the functions of the image processing unit 100 may be configured by software or hardware.

FIG. 5 is a block diagram showing a functional configuration of the screen generation unit 102. The screen generation unit 102 includes a dot cluster formation unit 200, a blank image formation unit 201, and a dot image formation unit 202. Each of these functions will be described later.

Note that some or all of the functions of the screen generation unit 102 may be configured by software or hardware.

The screen generation unit 102 of the present embodiment aims to improve the stability of image quality in the middle gradation, as described below.

When adding a new dot image in contact with the dot block db, the dot block forming unit 200 forms the dot block db so as to contact the dot block db with a predetermined number of dots or more in all the peripheral directions of the dot image. To do. The white image forming unit 201 forms the bridging portion dk with the minimum number of gradations when the growth of the dot cluster db progresses by the dot cluster forming unit 200 and the distance between the adjacent dot clusters db becomes equal to or less than a predetermined value. Then, the white dot portion ws is formed by connecting the adjacent dot blocks db. After the formation of the white halftone dot part ws is completed, the dot image forming unit 202 fills the white part formed in the white halftone dot part ws with the dot image. Specific examples of these functions will be described later.

The predetermined value of the distance between the dot clusters db is, for example, 50 μm.

Further, the white image forming section 201 forms the white halftone dot ws so that the number of gradations of the convex portion of the white halftone dot part ws having a short diameter of 50 μm is minimized.

The predetermined value of the distance between the dot clusters db is 50 μm, the input area ratio is 40% or less, and the white halftone dot portion ws is a halftone dot screen of 40% or more.

Further, the white image forming section 201 forms the cross-linked portion dk first in the direction of the larger screen angle when forming the white dot portion ws by forming the cross-linked portion dk from the halftone screen.

FIG. 6 is a flowchart showing an example of screen processing according to this embodiment. This process is executed by the screen generation unit 102 shown in FIGS. As an example of this screen processing, refer to FIG. 1 and FIGS. 2-1 to 2-3, for example.

First, the dot block formation unit 200 grows the dot block db according to the gradation value of the input image in the same manner as a normal halftone screen (step S101). Then, it is determined whether or not the distance dl between the dot clusters db is 50 μm or less in the process of dot growth (step S102). Here, if the distance dl of the dot db cluster is not equal to or less than 50 μm (determination, No), the process returns to step S101. On the other hand, if the distance dl between the dot clusters db exceeds 50 μm in step S102 (determination, Yes), the process proceeds to step S103. In this way, the dot cluster db is grown in the same manner as the conventional halftone dot screen until the distance dl between the dot clusters db becomes, for example, 50 μm.

Subsequently, the blank image forming unit 201 grows the dot cluster db that becomes the bridging portion dk in the first direction so that the halftone dot shape becomes the blank halftone dot portion ws (step S103). Then, the blank image forming unit 201 determines whether or not the bridge portion dk in the first direction has been formed (step S104). If the formation of the bridge portion dk in the first direction has not been completed (determination, No), the process returns to step S103. On the other hand, when the formation of the bridging portion dk in the first direction is completed in step S104 (determination, Yes), the white outline image forming unit 201 sets the halftone dot shape to the white halftone dot part ws in the second direction. A dot block db serving as a bridge portion dk is grown (step S105).

Then, the white image forming unit 201 determines whether or not the bridge portion dk in the second direction has been formed (step S106). Here, if the blank image forming unit 201 has not finished forming the bridging portion dk in the second direction (determination, No), the process returns to step S105. On the other hand, if the formation of the second-direction bridge portion dk is completed in step S106 (determination, Yes), the process proceeds to step S107. That is, in step S105, a dot block db serving as a bridging portion dk in the second direction is grown in order to change the halftone dot shape to the white halftone dot portion ws. Further, in step S106, the white dot portion ws is completed by growing the dot block db that becomes the bridge portion dk until it is connected to the adjacent dot block db. In this way, the white image forming unit 201 grows the dot cluster db that becomes the bridge portion dk until the adjacent dot clusters db are connected.

Then, the white image forming unit 201 grows the dot image of the bridging portion dk (step S107), and the bidirectional bridging portion dk on the outer periphery of the white dot portion ws becomes a line of 2 dots or more. It is determined whether or not it has become (step S108). Here, the blank image forming unit 201 returns to step S107 if the bridging portion dk in the two directions is not a line of 2 dots or more (determination, No). On the other hand, when the bridging portion dk in the two directions becomes a line of 2 dots or more (determination, Yes), the process proceeds to step S109.

That is, in step S107 and S108, the white image forming unit 201 has a line of 2 dots or more when the bridging portion dk in two directions which is the outer peripheral part of the white dot portion ws is a line of 2 dots or less. In this way, the dot cluster db is grown.

Subsequently, the blank image forming unit 201 grows the dot cluster db so that the fine convex portions of the blank halftone dot ws formed by the formation of the bridge portion dk are reduced as much as possible (step S109). After that, the blank image forming unit 201 determines whether or not the gradation value has reached the maximum in the blank halftone dot portion ws (step S110). If it is not the maximum value (determination, No), the process returns to step S109. .. On the other hand, when the gradation value reaches the maximum value in the white dot portion ws by the white image forming unit 201 (determination, Yes), the dot image forming unit 202 fills in the white dot portion ws. The dot block db is grown until it becomes solid.

Further, the screen processing in this embodiment will be described. FIG. 7 is a graph showing the image quality and its stability in the screen processing according to this embodiment. FIG. 7 shows image stability in the conventional halftone screen processing and the halftone screen processing of the present embodiment.

In FIG. 7, the horizontal axis represents the gradation value and the vertical axis represents the color stability (good to bad). As shown in FIG. 7, it can be confirmed that the conventional halftone screen processing (graph shown by a broken line) has a problem in color stability at a middle gradation. In addition, the degree of banding was poor because the part where the color stability is the worst and the gradation where banding is noticeable overlap. In FIG. 7, the vicinity of the right side of the top of the parabola of the graph shows a region where banding, which represents band-shaped density unevenness appearing in the halftone part (medium gradation part) of the image, is conspicuous. Note that banding is an abnormal image known as band-shaped density unevenness that appears in the halftone portion of an image.

On the other hand, the process (graph shown by the solid line) by the screen generation unit 102 of the present embodiment is, as shown by the solid line graph in FIG. 7, from the halftone dot shape→the halftone dot shape to the white halftone dot part ws. Of three image processing functions of the white dot portion ws. As a result, it can be confirmed that the above problems can be solved.

As described above, the dot block forming unit 200 grows in a dot shape until the distance between the dot blocks db becomes 50 μm, and when the distance between the dot blocks db becomes 50 μm, for example, the white dot part Start the formation of ws. Further, the blank image forming unit 201 forms the blank halftone dot portion ws by using a cross-linking structure in two types of directions. The formation of the white halftone dot portion ws is completed by the input area ratio of 40%. After the formation of the white halftone dot part ws is completed, the dot image forming part 202 grows the dot cluster db so as to fill the white halftone dot part ws.

Thus, the shape of the screen of the present embodiment grows through the following processes (see FIGS. 2-1 to 2-3). Therefore, in the screen processing of the present embodiment, the image quality and the stability of the image quality are improved by providing the following processing steps in the dot growth order performed by the blank image forming unit 201.
(1) Growth in halftone dot shape (2) Transition from halftone dot shape to open halftone dot shape (formation of first bridging part dk)
(3) Transition from halftone dot shape to open halftone dot shape (formation of second bridge portion dk)
(4) Growth in white dot shape

In the above-mentioned screen treatment, the first thing to be careful of is the dot growth order of the crosslinked structure for forming the white halftone dot portion ws. Immediately before the formation of the crosslinked structure, the distance between the dot clusters db is small, and the toner adhesion is unstable. Therefore, in order to improve the image quality and the stability of the image quality, it is necessary to connect the bridge portions dk that are about to be connected as quickly as possible. Further, in the white halftone dot portion ws, toner adhesion is likely to be unstable at the outer peripheral convex portion where the distance between the dot clusters db is narrow. From the above, in the dot growth order of the bridging portion dk and the blank halftone dot portion ws, particularly in the dot growth of the bridging portion dk, in the bridging structure extending from the adjacent dot clusters db, the distance between the dot clusters db is 50 μm. When the following occurs, the bridging portion dk is connected with the minimum number of gradations. Also, in the process of growing the dot cluster db of the white halftone dot part ws, dot growth is performed so that the number of gradations of the convex part having a short diameter of 50 μm is minimized.

As described above, in the halftone screen, since the distance between the dot clusters db becomes small, the toner adhesion becomes unstable, and the image quality and the stability of the image quality are impaired. The phenomenon occurs at an input area ratio of 50% in which the distance between the dot clusters db is less than 50 μm. Therefore, the screen generation unit 102 realizes the improvement of the image quality of the halftone screen and the stability of the image quality by performing the processes shown in FIGS. 2-1 to 2-3 described above.

As can be seen from FIG. 7, the halftone dot screen has two gradation portions where the stability of toner adhesion is poor. The first location is immediately before the first bridge portion dk is connected, and the second location is immediately before the second bridge portion dk is connected. This is because the distance between the dot clusters db is small immediately before the bridge portion dk is completed, and the stability of toner adhesion is poor. Banding exists as one of the abnormal images seen in electrophotography. Banding refers to the band-shaped density unevenness that appears in the halftone portion of the image as described above, and is most noticeable when the input area ratio indicating the black-white ratio of the dot image of the gradation value is around 50%. Therefore, the number of gradations to start forming the bridging part dk and the number of gradations required for the bridging part dk are determined so that the gradations at two locations where the bridging part dk is connected do not overlap the regions where banding is conspicuous. This makes it possible to reduce the occurrence of banding and improve the image quality and stability of the image quality at the middle gradation value.

Next, specific examples of the above-mentioned functional units will be described with reference to the drawings. In the present embodiment, by using a white dot shape which is a shape obtained by reversing the dot shape, it is possible to reduce the number of gradations with a smaller inter-dot distance than the halftone dot shape method which is a conventional dot screen growth method. cut back.

In the present embodiment, the dot block forming unit 200 forms a dot pattern until the distance between the dot blocks db becomes, for example, 50 μm, and thereafter, the blank image forming unit 201 forms the bridge part dk. After forming the cross-linking portion dk, switching to formation of the white halftone dot portion ws will be performed.

However, during the transition from the halftone dot shape to the formation of the white halftone dot portion ws, the distance between the dot clusters db becomes small and the image stability is not excellent. The banding described above is present as one of the abnormal images (image defects) found in the electrophotographic image forming apparatus. Banding is most noticeable when the input area ratio, which is the black-and-white ratio of the dot image, is around 50% (see FIG. 19 described above). Therefore, if the white halftone dot ws is formed in the vicinity of this gradation, banding will appear significantly. In order to suppress banding, the white image forming unit 201 finishes the formation of the white halftone dots ws by the input area ratio of 40% at which banding becomes conspicuous.

First, a description will be given of dot growth capable of obtaining toner adhesion stability at any gradation. In the electrophotographic system, the more dot images around the image, the higher the stability of toner adhesion tends to be. In particular, there is a large difference in the stability of toner adhesion depending on whether or not there are three or more dots around the newly arranged dot image. A specific example is shown in FIG.

FIG. 8 is an explanatory diagram showing a dot growth processing example according to the present embodiment. In FIG. 8, as the processing of the dot cluster db, the appropriate processing is shown in the OK example of (a), the inappropriate processing is shown in the NG example of (b), and an example of the exception is shown in (c).

The dot clump forming unit 200 performs the growth process of the dot clump db as shown in FIG. In FIG. 8, dn is a newly arranged dot image (1 dot), and ds is a contact side dot in contact with the dot block db.

As shown in FIG. 8A, when the dot cluster formation unit 200 adds a new dot image dn in contact with the dot cluster db, out of the eight directions around the dot image dn, three directions are provided in the dot cluster db. The above is formed so as to be in contact with each other (see ds in FIG. 8). In this manner, the dot cluster db is grown so that adjacent dot images are in contact with each other in three or more directions out of the eight surrounding directions with as many gradations as possible.

As described above, in electrophotography, an unstable feeble electric field is generated on the photoconductor, with or without toner around the toner.The feeble electric field also stabilizes the toner as the number of adjacent dot images increases. The size of the toner adheres and the toner adhesion is stable. By improving the stability of toner adhesion of each dot image, it is possible to improve image quality such as color stability and graininess in all gradation images.

Therefore, it is possible to improve the stability of toner adhesion at any gradation by going through the dot image growth process as shown in FIG. 8A, and as a result, the image quality of the gradation image is improved. And the stability of image quality can be aimed at.

On the other hand, in FIG. 8B, unlike the case of FIG. 8A, the newly arranged dot image dn is not in contact with the dot cluster db in the eight directions around the dot cluster db. Is unsuitable as a growth treatment.

Further, in FIG. 8C, no matter where the dot image dn is hit, the adjacent dots can only come into contact with each other in only two directions out of the eight surrounding directions. The condition of FIG. 8A cannot be satisfied depending on the case where the gradation is extremely small.

FIG. 9 is an explanatory diagram showing an example of a dot growth method until the inter-dot distance becomes 50 μm or less. The dot clump forming unit 200 grows the dot clumps db in order from the left side of FIG. 9 by using the conventional halftone dot forming method until the inter-dot distance becomes 50 μm. For example, when the resolution is 600 dpi, 1 dot≈42 μm, so dot clusters db are formed until the inter-dot distance becomes 1 dot. Further, when the resolution is 1200 dpi, 1 dot≈21 μm, and therefore the dot cluster db is formed in the conventional halftone dot shape until the inter-dot distance becomes 2 dots.

Since the distance between the dot clusters db becomes small during the formation of the white halftone dot portion ws from the halftone dot shape, the image stability tends to deteriorate. Therefore, in order to reduce the number of gradations in which the image quality and the stability of the image quality deteriorate, it is necessary to promptly complete the transition to the outline halftone dot shape. Therefore, a crosslinked structure as shown in FIG. 10 is used.

FIG. 10 is an explanatory diagram showing an example of a method of growing dots from the halftone dot shape to the white halftone dot portion ws. FIG. 11 is an explanatory diagram showing the relationship between the halftone dot shape and the screen angle. As shown in FIG. 11, the dot screen has a screen angle in two directions, a direction in which the screen angle Sθ is large and a direction in which the screen angle Sθ is small, by nature. First, a crosslinked structure is formed from the one having a larger screen angle. As shown in FIG. 11, when the bridge portion dk in the first direction is completed, it has a shape similar to the line screen shape. The reason is that the larger the screen angle of the line screen, the higher the image stability. is there. After the bridge portion dk having the larger screen angle is completed, the bridge portion dk having the smaller screen angle is completed to complete the transition to the white halftone dot portion ws.

In the example shown in FIG. 10, with respect to the halftone dot shape (maximum), formation of the halftone dot shape→white halftone dot portion ws is started to complete the bridge portion dk in the first direction, and finally, in the two directions. The cross-linking of the eyes is completed, and the formation of the white dot portions ws is completed. In the present embodiment, the processing for forming the crosslinked portion dk is performed as follows.

FIG. 12 is an explanatory diagram showing an example of the dot growth order in the blank image forming unit 201. In addition, in FIG. 12, as a forming process of the cross-linking portion dk, an appropriate screen process is shown as an OK example, and an inappropriate process is shown as an NG example.

Immediately before the bridging portion dk is joined, that is, when the bridging portion dk is completed with one dot as shown by a circle 301 in FIG. 12, the toner adhesion state deteriorates, and the image quality and the stability of the image quality are deteriorated. Becomes worse. Therefore, as shown in the OK example, if the bridging portion dk is not immediately connected at the next gradation, the toner adhesion state continues to be poor until the bridging portion dk is connected, and the image quality and the stability of the image quality deteriorate. Connected to.

The white image forming unit 201 forms the white halftone dot ws up to the input area ratio of 40% in order to make the banding inconspicuous. At that time, depending on the number of screen lines and the screen angle, it is necessary to form the white halftone dot portion ws in a state where the bridge portion dk is thin. An example thereof is shown in FIG.

FIG. 13 is an explanatory diagram showing a state immediately after the white halftone dot portion ws is formed by the different two-direction bridge portions dk. In FIG. 13A, the bridging portion dk is formed by a 1-dot line (a portion surrounded by a circle in the drawing). If the bridging portion dk is thus formed by one dot line in both directions, the toner adhesion on the bridging portion dk becomes unstable.

Therefore, as shown in FIG. 13B, in the growth of the white halftone dot portion ws, the dot growth is performed so that the bridge portion dk which is the outer periphery of the white halftone dot portion ws becomes one dot line. In this way, the white image forming unit 201, in the case where the bridging portion dk in the two directions, which is the outer periphery of the white halftone dot ws, is a line of 2 dots or less, the dot image is made to be a line of 2 dots or more. To form. This forming process is shown by a square portion in FIG. 13B (corresponding to a portion surrounded by a circle in FIG. 13A). As a result, it is possible to prevent deterioration in stability of toner adhesion after the white halftone dot ws is formed, and as a result, image quality and image quality stability are improved.

FIG. 14 shows the dot growth of the white dot portion ws formed by the bridging portions dk in different two directions. FIG. 14 shows a method for growing a white dot part ws in which the convex part of the white dot part ws is 2 dots. The upper part of FIG. 14 shows an appropriate growth example (OK example), and the lower part of FIG. The growth example (NG example) is shown.

In the electrophotography, as described above, when the distance between the dot clusters db is smaller than about 50 μm, toner adhesion becomes unstable. Therefore, for example, at 1200 dpi, a 1-dot convex portion is generated, and the toner adhesion in that area becomes unstable. Therefore, for example, as shown in the upper part of FIG. 14, by growing the dots so as to reduce the gradation of the convex portion where the distance between the dot clusters db is small as much as possible, it is possible to improve the image quality and stability in the white halftone dot portion ws. it can.

15 and 16 are explanatory diagrams showing an example in which the white halftone dot portions ws are formed so that the dot images are arranged linearly in the main scanning direction. FIG. 15 is an inappropriate example (NG example) in the arrangement of the dot images. FIG. 16 is a suitable example (OK example) in the arrangement of the dot images.

When the dot images are arranged in the main scanning direction and linearly, if the white dot portions ws are grown as shown in FIG. 15, the screen angle Sθ of this screen image cannot be utilized. In the case of FIG. 15, the screen angle of 0 degree, which is not excellent in image quality stability, is strongly influenced.

Therefore, in the case of the shape shown in FIG. 15, the white image forming unit 201 forms the white halftone dot portion ws along the screen angle Sθ. Therefore, the white image forming portion 201 forms the white halftone dot portion ws along the screen angle Sθ as shown in FIG. 16, thereby deteriorating the stability of toner adhesion of the white halftone dot portion ws. By avoiding this, image quality is improved and image quality is stabilized. In this way, when the dot images are grown so as to fill the white halftone dot portions ws, the dot images are not aligned in the main scanning direction and linearly.

FIG. 17 shows an example of the difference in image stability between the conventional halftone dot screen and the halftone dot screen of this embodiment in terms of image quality and stability. FIG. 17 uses color stability on the vertical axis. It can be confirmed that the conventional halftone screen (graph shown by a broken line) has a problem in color stability in the middle gradation. On the other hand, the screen (graph indicated by a solid line) of the present embodiment has three stages of halftone dot shape→formation of cross-linking part dk for forming halftone dot shape to halftone dot shape→white dot shape. Have a pattern. As described above, it can be confirmed that the color stability in the middle gradation can be improved as compared with the conventional halftone dot screen by having the above-described method of growing the bridge portion dk and the white halftone dot portion ws.

By the way, the program executed by the image processing apparatus according to the present embodiment is provided by being pre-installed in the ROM 111 or the like. The program is recorded in a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, or a DVD (Digital Versatile Disk) in the form of an installable or executable file. May be provided.

Further, the program executed in the present embodiment may be stored in a computer connected to a network such as the Internet and provided by being downloaded via the network. Further, the program executed in this embodiment may be provided or distributed via a network such as the Internet.

The program executed in this embodiment has a module configuration including the above-mentioned units. As actual hardware, a CPU (processor) 110 reads out a program from the ROM 111 and executes the program to load the above-mentioned respective parts onto a main storage device and generate the respective parts onto the main storage device.

The above-described embodiment is presented as an example for realizing the present invention, and is not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. Further, these embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

100 image processing unit 101 image determination unit 102 screen generation unit 103 dither processing unit 105 PMW unit 110 CPU
111 ROM
112 RAM
120 image forming unit 200 dot cluster forming unit 201 blank image forming unit 202 dot image forming unit

JP 2012-3180A

Claims (18)

An image determination unit that determines the gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. will then, when said distance of said dot Katamarikan adjacent in the growth process of the dot masses is equal to or less than a predetermined value, by connecting the minimum the dot masses adjacent to form a crosslinked portion in number of gradations A screen generation unit for forming a white dot image ,
The screen generation unit,
When arranging a new dot image in contact with the dot block, the new dot image is arranged so as to contact the dot block in three or more directions out of the eight directions around the dot image. A dot cluster forming portion to be formed,
When the growth of the dot clusters progresses by the dot cluster formation unit and the distance between the adjacent dot clusters becomes equal to or less than a predetermined value, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. With a white image forming unit that forms a white halftone image with
After the formation of the blank halftone dot image is completed, a dot image forming unit that fills the blank portion formed in the blank halftone dot image with a dot image,
An image processing apparatus comprising: An image determination unit that determines the gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. When the distance between the adjacent dot clusters becomes less than or equal to a predetermined value in the process of growing the dot clusters, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A screen generation unit for forming a white dot image,
The screen generation unit,
When arranging a new dot image in contact with the dot cluster, out of all directions around the dot image, a dot cluster forming unit that grows the dot cluster so as to contact the dot cluster with a predetermined number of dots or more. ,
When the growth of the dot clusters progresses by the dot cluster formation unit and the distance between the adjacent dot clusters becomes equal to or less than a predetermined value, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. With a white image forming unit that forms a white halftone image with
After the formation of the white halftone dot image is completed, a dot image forming unit for filling the white blank part formed in the white halftone dot image with a dot image,
The blank image forming unit forms a dot image so as to be a line of 2 dots or more when the bridging portion in two directions, which is the outer periphery of the blank halftone image, is a line of 2 dots or less. Image processing device. An image determination unit that determines the gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. When the distance between the adjacent dot clusters becomes less than or equal to a predetermined value in the process of growing the dot clusters, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A screen generation unit for forming a white dot image,
The image processing apparatus, wherein the predetermined value of the distance between the dot clusters is 50 μm. An image determination unit that determines the gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. When the distance between the adjacent dot clusters becomes less than or equal to a predetermined value in the process of growing the dot clusters, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A screen generation unit for forming a white dot image,
The screen generation unit,
When arranging a new dot image in contact with the dot cluster, out of all directions around the dot image, a dot cluster forming unit that grows the dot cluster so as to contact the dot cluster with a predetermined number of dots or more. ,
When the growth of the dot clusters progresses by the dot cluster formation unit and the distance between the adjacent dot clusters becomes equal to or less than a predetermined value, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. With a white image forming unit that forms a white halftone image with
After the formation of the white halftone dot image is completed, a dot image forming unit for filling the white blank part formed in the white halftone dot image with a dot image,
The white image forming unit forms the dot image such that the number of gradations of the convex portion of the white halftone image having a short diameter of 50 μm is minimized. An image determination unit that determines the gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. When the distance between the adjacent dot clusters becomes less than or equal to a predetermined value in the process of growing the dot clusters, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A screen generation unit for forming a white dot image,
The image processing apparatus, wherein the predetermined value of the distance between the dot clusters is 50 μm, the input area ratio is 40% or less, and the white halftone dot image is a halftone dot screen of 40% or more. The screen generation unit,
When placing a new dot image in contact with the dot mass of all directions around the dot image, and the dot masses forming part of growing the dot masses in contact with a predetermined number of dots than the dot mass ,
The dot lump forming portion and advances the growth of the dot masses, if the distance of the dot Katamarikan adjacent falls below a predetermined value, connects with the dot masses adjacent to each other to form a bridging portion with a minimum number of gradations With a white image forming unit that forms a white halftone image with
After the formation of the blank halftone dot image is completed, a dot image forming unit that fills the blank portion formed in the blank halftone dot image with a dot image,
The image processing device according to claim 3, further comprising: The white image forming unit, the image processing according to at least one of claims 1, 2, 4 and 6 and forming a hollow halftone image along the screen angle of the halftone screen has apparatus. The blank image forming unit forms the cross-linking portion first in a direction having a larger screen angle of the half-tone dot screen when forming the blank half-tone dot image by forming the cross-linking portion from the half-tone dot screen. The image processing device according to at least one of claims 1, 2, 4, and 6 . An image determination step of determining a gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. will then, when said distance of said dot Katamarikan adjacent in the growth process of the dot masses is equal to or less than a predetermined value, by connecting the minimum the dot masses adjacent to form a crosslinked portion in number of gradations A screen generation step for forming a white dot image,
The screen generation step,
When arranging a new dot image in contact with the dot block, the new dot image is arranged so as to contact the dot block in three or more directions out of the eight directions around the dot image. A dot lump formation step of growing,
When the growth of the dot clusters progresses due to the dot cluster formation step and the distance between the adjacent dot clusters becomes equal to or less than a predetermined value, a bridge portion is formed with the minimum number of gradations and connected to the adjacent dot clusters. A white image forming step of forming a white halftone image with
After the formation of the white dot image is completed, a dot image forming step of filling the white part formed in the white dot image with a dot image,
An image processing method comprising: An image determination step of determining a gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. When the distance between the adjacent dot clusters becomes less than or equal to a predetermined value in the process of growing the dot clusters, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A screen generation step for forming a white dot image,
The screen generation step,
When arranging a new dot image in contact with the dot cluster, out of all directions around the dot image, a dot cluster forming step of growing the dot cluster so as to contact the dot cluster with a predetermined number of dots or more. ,
When the growth of the dot clusters progresses due to the dot cluster formation step and the distance between the adjacent dot clusters becomes equal to or less than a predetermined value, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A white image forming step of forming a white halftone image with
After the formation of the white dot image is completed, a dot image forming step of filling the white part formed in the white dot image with a dot image,
In the blank image forming step, when the bridging portion in the two directions, which is the outer periphery of the blank halftone image, is a line of 2 dots or less, a dot image is formed to be a line of 2 dots or more. Image processing method. An image determination step of determining a gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. When the distance between the adjacent dot clusters becomes less than or equal to a predetermined value in the process of growing the dot clusters, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A screen generation step for forming a white dot image,
The image processing method, wherein the predetermined value of the distance between the dot clusters is 50 μm. An image determination step of determining a gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. When the distance between the adjacent dot clusters becomes less than or equal to a predetermined value in the process of growing the dot clusters, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A screen generation step for forming a white dot image,
The screen generation step,
When arranging a new dot image in contact with the dot cluster, out of all directions around the dot image, a dot cluster forming step of growing the dot cluster so as to contact the dot cluster with a predetermined number of dots or more. ,
When the growth of the dot clusters progresses due to the dot cluster formation step and the distance between the adjacent dot clusters becomes equal to or less than a predetermined value, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A white image forming step of forming a white halftone image with
After the formation of the white dot image is completed, a dot image forming step of filling the white part formed in the white dot image with a dot image,
The white image forming step is an image processing method in which a dot image is formed so that the number of gradations of a convex portion having a short diameter of 50 μm of the white halftone image is minimized. An image determination step of determining a gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. When the distance between the adjacent dot clusters becomes less than or equal to a predetermined value in the process of growing the dot clusters, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A screen generation step for forming a white dot image,
The predetermined value of the distance between the dot clusters is 50 μm, the input area ratio is 40% or less, and the white halftone dot image is a halftone dot screen of 40% or more. An image determination step of determining a gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. will then, when said distance of said dot Katamarikan adjacent in the growth process of the dot masses is equal to or less than a predetermined value, by connecting the minimum the dot masses adjacent to form a crosslinked portion in number of gradations Causing the computer to execute a screen generation step for forming a white dot image ,
The screen generation step,
When arranging a new dot image in contact with the dot block, the new dot image is arranged so as to contact the dot block in three or more directions out of the eight directions around the dot image. Dot cluster formation step to grow,
When the growth of the dot clusters progresses due to the dot cluster formation step and the distance between the adjacent dot clusters becomes equal to or less than a predetermined value, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A white image forming step for forming a white dot image with
After the formation of the white dot image is completed, a dot image forming step of filling the white part formed in the white dot image with a dot image,
Programs that include. An image determination step of determining a gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. When the distance between the adjacent dot clusters becomes less than or equal to a predetermined value in the process of growing the dot clusters, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. Causing the computer to execute a screen generation step for forming a white dot image,
The screen generation step,
When arranging a new dot image in contact with the dot cluster, out of all directions around the dot image, a dot cluster forming step of growing the dot cluster so as to contact the dot cluster with a predetermined number of dots or more, ,
When the growth of the dot clusters progresses due to the dot cluster formation step and the distance between the adjacent dot clusters becomes equal to or less than a predetermined value, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A white image forming step for forming a white dot image with
After the formation of the white dot image is completed, a dot image forming step of filling a white part formed in the white dot image with a dot image,
In the blank image forming step, when the bridging portion in two directions, which is the outer periphery of the blank halftone image, is a line of 2 dots or less, a dot image is formed so as to be a line of 2 dots or more. program. An image determination step of determining a gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. When the distance between the adjacent dot clusters becomes less than or equal to a predetermined value in the process of growing the dot clusters, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. Causing the computer to execute a screen generation step for forming a white dot image,
The program, wherein the predetermined value of the distance between the dot clusters is 50 μm. An image determination step of determining a gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. And, when the distance between the adjacent dot clusters in the growth process of the dot clusters is less than or equal to a predetermined value, a bridging portion is formed with the minimum number of gradations to form the adjacent dot clusters. A screen generation step of connecting to form a white halftone dot image, and causing the computer to execute,
The screen generation step,
When arranging a new dot image in contact with the dot block, in all the peripheral directions of the dot image, a dot block forming step of forming the dot block so as to contact the dot block with a predetermined number of dots or more. ,
When the growth of the dot clusters progresses due to the dot cluster formation step and the distance between the adjacent dot clusters becomes equal to or less than a predetermined value, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. A white image forming step for forming a white dot image with
After the formation of the white halftone dot image is completed, a dot image forming step of filling a white part formed in the white halftone dot image with a dot image,
The program for forming a blank image is a program for forming a dot image so that the number of gradations of a convex portion having a short diameter of 50 μm of the blank halftone image is minimized. An image determination step of determining a gradation value for each predetermined range with respect to the input image data,
When the input area ratio indicating the black-and-white ratio of the dot image of the gradation value is smaller than the value at which the image defect appears, the dot image is arranged around each of the plurality of growth centers of the halftone screen to grow the dot cluster. When the distance between the adjacent dot clusters becomes less than or equal to a predetermined value in the process of growing the dot clusters, a bridge portion is formed with the minimum number of gradations to connect the adjacent dot clusters. Causing the computer to execute a screen generation step for forming a white dot image,
A program in which the predetermined value of the distance between the dot clusters is 50 μm, the input area ratio is 40% or less, and the white halftone dot image is a halftone dot screen of 40% or more.

Images