JP2009211546A - Image processing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reproduce the line width and density of an original image even when thinning a line of a line width and a character of any size, in an electrophotographic type image forming apparatus. <P>SOLUTION: A rasterization part generates a 1,200-dpi (dot/inch) raster image from PDL (Page Description Language) data received from the outside, and outputs it to a resolution conversion part. The raster image is developed to 2,400 dpi by the resolution conversion part, and is applied with line thinning processing two times by a line thinning processing part. As a result, the raster images having line thinning amounts of "1", "2" are respectively stored in an image memory. A tag output part of a controller generates a tag according to the line width or the like from the PDL data received from the outside, and outputs it to the resolution conversion part. The resolution conversion part develops the output tag to 2,400 dpi, and outputs it to a selection part. The selection part selects the raster image of the proper line thinning amount from the image memory in each pixel, and outputs a selection result thereof to a control part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image forming apparatus.

In the electrophotographic image forming apparatus, the boundary portion of the electrostatic latent image may be blurred due to the characteristics of the photosensitive member. For this reason, the width of the line image formed on the surface of the recording material is increased, and for example, a small character of 5 points or less may be crushed and cannot be literate. As methods for improving the blur of the electrostatic latent image, it is generally known to reduce the beam diameter at the time of exposure and to reduce the film thickness of the photoreceptor film. In addition to these, image data is controlled. Therefore, a technique for improving the collapse of fine lines and characters has been developed. Patent Document 1 discloses a technique for performing thinning by detecting a boundary portion of an image called an edge by inspecting each pixel included in a 5 pixel × 5 pixel window centered on a target pixel. ing.
JP 2005-341249 A

FIG. 16 is a flowchart showing an example of a thinning process flow in the image forming apparatus. In this figure and the following description, a unit of “dpi” is used as an index of resolution. This means dot / inch, that is, the number of pixels per inch.
The image forming apparatus first performs rasterization for converting image data described in a page description language (hereinafter referred to as PDL: Page Description Language) into a 1200 dpi raster image (step Sc01), and then performs resolution conversion to 2400 dpi. Is converted into a raster image (step Sc02). Here, the resolution conversion simply increases the resolution of the raster image, whereby a raster image matching the resolution at the time of image formation can be obtained. One pixel, which is the minimum unit constituting a 1200 dpi raster image, is represented by 2 pixels × 2 pixels, that is, 4 pixels when converted to a 2400 dpi raster image. The raster image of 2400 dpi thus obtained is thinned by thinning processing (step Sc03), and then image forming processing is performed (step Sc04). As a result, a 2400 dpi image corresponding to the thinned raster image is formed on the surface of the recording material such as paper.

Here, the thinning process will be described. Thinning processing is a process in which a raster image is inspected for each pixel, and when a group of pixels including the pixel satisfies a predetermined condition, the pixel is replaced with a background pixel, that is, a pixel of a different color. In this way, the image is thinned. There are various known methods for thinning processing. As an example, a contraction algorithm and a Hilditch thinning algorithm will be described.
FIG. 17A shows a window used for the thinning process. The window shown in the drawing is a 3 × 3 pixel (3 rows × 3 columns) window in which peripheral pixels P _{1 to} P ₈ surround the center pixel of interest P ₀ . Here, when the number of pixels on one side of the pixel group constituting the window used for the thinning process is “window size w”, the window size w of this window is “3”. The contraction algorithm or the Hilitch thinning algorithm checks the relationship between the peripheral pixels P _{1 to} P ₈ and the target pixel P _0, and if this relationship meets a predetermined condition, the target pixel P ₀ is deleted as a candidate for deletion. That is, it is set as a replacement candidate for a pixel of a different color.
FIG. 17B is a diagram illustrating scanning for a raster image. The grid shown in the figure represents each pixel constituting the raster image. In the thinning process, each pixel included in the raster image is sequentially inspected as a target pixel one by one along the arrow Rs shown in the drawing. That is, the target pixel is inspected in the main scanning direction (the direction from the left to the right in the figure and is the “row” direction), and when it is inspected to the right end, the pixel returns to the left end and the scanning line is changed to the sub-scanning direction (upper in the figure The pixel is moved by one pixel in the “column” direction, and the target pixel is inspected in the main scanning direction. The deletion candidate pixels determined through such an inspection are collectively replaced with a background color pixel, for example, a white pixel, by a subsequent deletion process.
FIG. 17C is a diagram showing a deletion candidate determination method in the contraction algorithm. In the contraction algorithm, the target pixel P ₀ is a black pixel (hereinafter referred to as a black pixel), and at least _{one of} the peripheral pixels P _{1 to} P ₈ is a white pixel (hereinafter referred to as a white pixel). in this case, the target pixel P ₀ is a deletion candidate pixel. For example, as shown in the left diagram of FIG. 17C, when the pixel P _{0 at} the upper left, that is, when the peripheral pixel P ₄ is a white pixel, the pixel of interest P ₀ is a deletion candidate pixel as shown in the right diagram. After the deletion process, the pixel is replaced with a white pixel.

Next, the thinning algorithm of Hilditch will be briefly described.
The thinning algorithm of the Hitchitch is a case where the pixel of interest P ₀ in the 3 pixel × 3 pixel window shown in FIG. 17A satisfies the following six conditions in relation to the peripheral pixels P _{1 to} P _8. Furthermore, this is an algorithm in which the target pixel P ₀ is a deletion candidate.
<Condition 1> The target pixel P ₀ is a graphic element (for example, a black pixel having a color different from that of a white pixel in the background).
<Condition 2> The target pixel P ₀ is a boundary point.
<Condition 3> target pixel _{P 0} is, not an end point.
<Condition 4> The target pixel P ₀ is not an isolated point.
<Condition 5> Even if the pixel of interest P ₀ is deleted, the connectivity of surrounding pixels is preserved.
<Condition 6> The target pixel P ₀ forms a line with a width of 2 pixels, and even if this is deleted, only one side of the line is deleted.

  FIG. 18 is a diagram showing the relationship between the input line width and the output line width for each number of thinning processes when the Hilditch thinning algorithm is used as the thinning process. In this figure, the relationship between the input line width and the output line width in offset printing is shown for comparison, but in the case of offset printing, any input line width is substantially equal to the output line width, so It can be seen that an image close to an image (that is, an image represented by image data described in a page description language) is printed. On the other hand, in electrophotographic printing, the reproducibility of the original image is significantly different between a region with a large input line width and a region with a small input line width. For example, as shown in the figure, when the input line width is 84.66 μm or more, the output line width is larger than the input line width when the thinning process is not performed and when the thinning process is performed once. When the thinning process is performed twice, the output line width becomes a value that is substantially close to the input line width. Therefore, the reproducibility of the original image is higher when the thinning process is performed twice. However, when the input line width is less than 84.66 μm, the output line width is much smaller than the input line width when the thinning process is performed twice, but the output is reduced when the thinning process is performed once. Since the line width is a value substantially close to the input line width, the reproducibility of the original image is higher when the thinning process is performed once.

  FIG. 19 is a diagram showing the relationship between the input line width and the output density for each number of thinning processes when the Hilditch thinning algorithm is used as the thinning process described above. As shown in the figure, when the input line width is 84.66 μm or more, in all cases of the electrophotographic system, the output density is slightly darker or comparable to that of offset printing. However, when the input line width is less than 84.66 μm, if the thinning process is performed, the output density becomes lower than that of the offset printing, and particularly if the thinning process is performed twice, the output density becomes extremely low.

  From the above, it can be seen that in the electrophotographic system, the relationship between the input line width and the output line width and the relationship between the input line width and the output density are not linearly proportional due to the characteristics of the image forming apparatus. Therefore, if the number of thinning processes is fixed regardless of the input line width of the original image to be printed, if the input line width becomes smaller, the output line width becomes remarkably smaller and the output density becomes remarkably thinner, resulting in faint printing. Or disappear.

  An object of the present invention is to reproduce an image close to the line width and density of an original image regardless of the size of the character and the line width in an electrophotographic image forming apparatus.

  In order to solve the above-described problems, an image processing apparatus according to the present invention includes a raster image acquisition unit that acquires a raster image that is image data expressed in a raster format, and a raster image acquired by the raster image acquisition unit. A raster image generating means for generating a plurality of raster images having different thinning amounts, and a specification for acquiring designation information for specifying a thinning amount for each pixel included in the raster image acquired by the raster image acquiring means A raster image corresponding to the amount of thinning specified by the acquired designation information is selected for each pixel from the plurality of raster images generated by the information acquisition unit and the raster image generation unit, and an image based on the raster image is selected. To the image forming means for forming the selected raster image. Characterized by comprising a means.

  The image processing apparatus according to the present invention includes a raster image acquisition unit that acquires a raster image that is image data expressed in a raster format, and a thinning amount using the raster image acquired by the raster image acquisition unit. A raster image generating means for generating a plurality of different raster images, and whether a pixel group consisting of each pixel included in the raster image acquired by the raster image acquiring means and its surrounding pixels satisfies a predetermined condition By means of the designation information generated from the plurality of raster images generated by the raster image generation means, the designation information generation means for generating designation information for specifying the thinning amount for each pixel included in the raster image Select a raster image for each pixel according to the specified thinning amount and With respect to an image forming means for forming a basis image over di-, characterized by comprising a selection means for outputting the raster image selected.

  Preferably, the raster image generation means converts the raster image acquired by the raster image acquisition means into a raster image having a resolution higher than the resolution of the raster image, and conversion by the resolution conversion means. When a pixel group consisting of each pixel included in the obtained raster image and its surrounding pixels satisfies a predetermined condition, the pixel is thinned by replacing each pixel with a pixel of a different color. If a pixel group consisting of one thinning means and each pixel included in the raster image thinned by the first thinning means and surrounding pixels satisfies a predetermined condition, Second thinning means for thinning the image by replacing with pixels of different colors may be provided.

  Preferably, the raster image generation unit converts the raster image acquired by the raster image acquisition unit into a raster image having a resolution higher than the resolution of the raster image, and is included in the converted raster image. A first thinning means for thinning an image by substituting each pixel with a pixel of a different color when the pixel group consisting of each pixel and its surrounding pixels satisfies a predetermined condition; When a pixel group consisting of each pixel included in the raster image acquired by the image acquisition means and its surrounding pixels satisfies a predetermined condition, the pixel is replaced with a pixel of a different color and the thin line of the image Second thin line for converting the thinned raster image into a raster image having a resolution higher than the resolution of the raster image May and means.

  Preferably, the raster image generation unit stores a correspondence relationship between an arrangement pattern of a plurality of pixels and a raster image having a resolution higher than the resolution of the raster image acquired by the raster image acquisition unit. The input raster obtained by collating the arrangement pattern of each pixel of the raster image acquired by the raster image acquisition means and the surrounding pixels with the arrangement pattern stored in the correspondence storage means A pixel group consisting of a replacement unit that replaces an image with a raster image associated with an arrangement pattern that matches the raster image, and each pixel included in the raster image that has been replaced by the replacement unit and its surrounding pixels. If the predetermined condition is satisfied, each pixel is placed in a different color pixel. A first thinning means for thinning the image, and a pixel group composed of each pixel included in the raster image replaced by the first thinning means and the surrounding pixels satisfy a predetermined condition. In this case, it is preferable to include second thinning means for thinning the image by replacing each pixel with a pixel of a different color.

  In the above-described aspect, the pixel group when the first thinning unit and the second thinning unit perform thinning includes the pixels and peripheral pixels surrounding the pixel as a center. A pixel group of 3 rows and 3 columns is desirable.

An image forming apparatus according to the present invention includes the above-described image processing apparatus and an image forming unit that forms an image based on a raster image output from the selection unit of the image processing apparatus.
Preferably, the image forming unit includes an image holding member, a charging unit that charges the surface of the image holding member, and an exposure unit that exposes the surface of the image holding member charged by the charging unit to form a latent image. A latent image forming means; a developing means for developing the latent image by supplying a developer to the surface of the image carrier on which the latent image is formed; and a transfer means for transferring the image obtained by the development to a recording medium; The exposure means latent image forming means reduces the amount of light when exposing the surface of the image carrier when the thinning amount in the raster image selected by the selection means is large, and the selection means When the amount of thinning in the selected raster image is small, it is preferable to increase the amount of light when exposing the surface of the image carrier.

  In addition, an image forming apparatus according to the present invention generates the raster image and the designation information by analyzing the description data describing the content of the image, and the raster image data. Supply means for supplying the specified information to the specified information acquiring means, and an image forming means for forming an image based on the raster image output from the selecting means of the image processing apparatus. It is characterized by providing.

  According to the present invention, in an electrophotographic image forming apparatus, an image close to the line width and density of the original image can be reproduced regardless of the size of the character and the line width.

Embodiments of the present invention will be described below with reference to the drawings.
[A. First embodiment]
[A-1. Constitution]
FIG. 1 is a diagram showing a structure of an image forming apparatus 1 according to the first embodiment of the present invention.
As shown in FIG. 1, the image forming apparatus 1 includes a paper storage unit 12, image forming units 13Y, 13M, 13C, and 13K, a transfer unit 14, and a fixing unit 15. Each of these components is controlled by a control unit 1020, which will be described later, and functions as an image forming unit that forms a toner image based on a raster image that is raster format image data. The resolution of the image formed by this image forming unit is, for example, 2400 dpi. Note that the symbols Y, M, C, and K indicate configurations corresponding to yellow, magenta, cyan, and black toners, respectively. The paper storage unit 12 stores paper cut into a predetermined size such as A3 or A4. The sheets stored in the sheet storage unit 12 are picked up one by one by a pickup roller or the like, and are conveyed to the transfer unit 14 via a sheet conveyance path.

  The image forming units 13Y, 13M, 13C, and 13K respectively expose the surface of the photosensitive drum that has been charged by the charging unit, the charging unit that charges the surface of the photosensitive drum that is the image carrier, and the latent image. A latent image forming unit for forming an image, a developing unit for supplying the toner as a developer to the surface of the photosensitive drum on which the latent image is formed by the latent image forming unit, a primary transfer roll, and a cleaning member; A toner image corresponding to the raster image is formed and transferred onto the intermediate transfer belt 141 of the transfer unit 14 in a superimposed manner. The transfer unit 14 includes an intermediate transfer belt 141, a secondary transfer roll 142, and an opposing roll 143 that faces the secondary transfer roll 142 with the intermediate transfer belt 141 interposed therebetween, and the image forming units 13Y, 13M, and 13C. , 13K, a transfer means for transferring the toner image obtained by the developing unit to a sheet. The intermediate transfer belt 141 is rotated in a direction A in the figure by a driving roll (not shown), and when the toner images are transferred in an overlapping manner by the image forming units 13Y, 13M, 13C, and 13K, the toner images are transferred to the intermediate transfer belt 141. It is conveyed to the position of the next transfer roll 142 and the opposing roll 143. The secondary transfer roll 142 transfers the toner image on the intermediate transfer belt 141 to the sheet conveyed from the sheet storage unit 12 by the potential difference with the intermediate transfer belt 141. The sheet on which the toner image is transferred from the intermediate transfer belt 141 is conveyed to the fixing unit 15.

The fixing unit 15 includes a heating roll 151 and a pressure roll 152. The sheet conveyed from the secondary transfer roll 142 is sandwiched between the heating roll 151 and the pressure roll 152, and heat and pressure are applied to the sheet. In addition, the toner image is fixed on the paper. The heating roll 151 has a heat source such as a halogen lamp inside, and heats the surface of the paper to about 100 degrees. The pressure roll 152 is pressed against the heating roll 151 and applies pressure to the sheet passing between the heating roll 151 and the pressure roll 152. In addition, a peeling member 153 made of metal or resin is provided near the surface of the heating roll 151. The paper that has undergone the fixing process by applying heat and pressure by the heating roll 151 and the pressure roll 152 is peeled off from the heating roll 151 by the peeling member 153 and discharged by two guides 154 that form a paper transport path. Guided to mouth 19.
The above is the structure of the image forming apparatus 1.

FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus 1.
The image forming apparatus 1 includes a controller 1000, an image processing unit 1010, a control unit 1020, an image memory 1030, an operation unit 1040, a display unit 1050, and an image forming unit 1060. The image forming apparatus 1 is communicably connected to an external PC 2 such as a personal computer by wire or wireless, and receives image data described in PDL (hereinafter referred to as PDL data) from the external PC 2. The controller 1000 includes a rasterizing unit 1001 and a tag output unit 1002. The rasterization unit 1001 of the controller 1000 performs rasterization based on the PDL data received from the external PC 2 to generate a 1200 dpi raster image, and outputs the raster image to the image processing unit 1010. Further, the tag output unit 1002 of the controller 1000 extracts information relating to the line width and character size from the PDL data. The tag output unit 1002 generates a tag corresponding to the extracted information by referring to the tag table stored in the table storage unit 10021, and outputs the tag to the image processing unit 1010. Such a tag is generated for each 1200 dpi pixel of the raster image output from the rasterizing unit 1001 and is designation information for designating a thinning amount in thinning processing described later. That is, the controller 1000 is a supply unit that analyzes PDL data, which is description data describing the contents of an image, generates a raster image and a tag, and supplies these to an image processing unit.
FIG. 3 is a diagram illustrating an example of a tag table stored in the table storage unit 10021. In the tag table, a tag type, a line width, and a character size (that is, the number of points) are described in association with each other. For example, when the line width is less than 84.66 μm, the tag is “1”, and when the Mincho character is 6 pt or more, the tag is “2”.

  Returning to FIG. 2, the description will be continued. The acquisition unit 1019 of the image processing unit 1010 acquires the above-described 1200 dpi raster image from the controller 1000 and acquires a tag (specification information) that specifies the thinning amount for each pixel included in the raster image. That is, the acquisition unit 1019 of the image processing unit 1010 functions as a raster image acquisition unit and also functions as a designation information acquisition unit. The resolution conversion unit 1012 of the image processing unit 1010 converts the resolution of the 1200 dpi raster image output by the controller 1000 into a 2400 dpi raster image having a higher resolution and outputs the raster image to the image memory 1030. Also, the resolution conversion unit 1012 expands the tag output by the tag output unit 1002 to 2400 dpi and outputs the tag to the selection unit 1014. In this process, the tag for one pixel of 1200 dpi is simply replaced with the tag for 2 × 2 pixels (ie, four pixels) of 2400 dpi corresponding to the position without changing the tag type.

  The image memory 1030 stores a 2400 dpi raster image output from the resolution conversion unit 1012. The thinning processing unit 1013 of the image processing unit 1010 performs thinning processing on the 2400 dpi raster image stored in the image memory 1030 using the window with the window size w = 3 described above based on the Hilditch thinning algorithm. The raster image generated thereby is output to the image memory 1030. Further, the thinning processing unit 1013 of the image processing unit 1010 performs the second thinning process on the raster image that has been subjected to the thinning process once, and the generated raster image is stored in the image memory 1030. Output. That is, the thinning processing unit 1013 of the image processing unit 1010 functions as a first thinning unit that generates a raster image having a thinning amount of “1”, and generates a raster image having a thinning amount of “2”. It functions as the second thinning means. The resolution conversion unit 1012 and the thinning processing unit 1013 of the image processing unit 1010 function as a raster image generation unit that generates a plurality of raster images having different thinning amounts using the raster image acquired by the acquisition unit 1019. To do.

  The selection unit 1014 selects an appropriate thinning amount for each pixel from the raster image thinned by the thinning processing unit 1013 according to the tag received by the acquisition unit 1019 from the tag output unit 1002 of the controller 1000. A raster image is selected, and the selection result is output to the control unit 1020. For example, when the tag for a certain pixel is “1”, the selection unit 1014 selects a raster image that has been thinned once for the corresponding pixel, and when the tag is “2” That is, a raster image that has been thinned twice for a pixel to be selected is selected.

  The control unit 1020 is a CPU (Central Processing Unit) or the like, and controls each unit of the image forming apparatus 1. Further, the control unit 1020 outputs the raster image selected by the selection unit 1014 to the image forming unit. In other words, the selection unit 1014 and the control unit 1020 have a raster image corresponding to the thinning amount specified by the tag received by the acquisition unit 1019 from the plurality of raster images generated by the resolution conversion unit 1012 and the thinning processing unit 1013. For each pixel, and functions as a selection unit that outputs the selected raster image to the image forming unit 1060. The display unit 1050 is, for example, a liquid crystal display device, and displays an interactive screen with the user and various types of information based on data provided from the control unit 1020. The operation unit 1040 includes buttons, switches, and the like. The operation unit 1040 receives an operation by a user and supplies a signal corresponding to the operation content to the control unit 1020. The image forming unit 1060 is an image forming unit that includes the paper storage unit 12 described above, the image forming units 13Y, 13M, 13C, and 13K, the transfer unit 14, the fixing unit 15, and the like. An image forming process is performed on the basis of the raster image read and transferred from, and an image is formed on the surface of a recording material (for example, paper).

[A-2. Operation]
Next, the operation of the image forming apparatus 1 according to the first embodiment and the effects produced by the image forming apparatus 1 will be described.
FIG. 4 is a diagram illustrating a processing flow of the image forming apparatus 1. First, when receiving the PDL data from the external PC 2, the rasterizing unit 1001 of the controller 1000 performs rasterization, and the resolution is lower than the resolution 2400 dpi of the image forming means and more than half of the resolution, in this case, just a half of the 1200 dpi raster. Generate an image. The 1200 dpi raster image obtained in this way is sent to the image processing unit 1010 of the image forming apparatus 1 and converted into a 2400 dpi raster image, which is the resolution of the image forming means, by the resolution conversion unit 1012. The raster image is subjected to thinning processing by the thinning processing unit 1013 of the image processing unit 1010. Here, after the thinning process is performed once, the second thinning process is further performed based on the raster image after the thinning process, and after the thinning process is performed once (that is, the thinning process is performed). The raster image with the amount “1”) and the raster image after the thinning process is performed twice (that is, the thinning amount is “2”) are stored in the image memory 1030, respectively.

  On the other hand, when receiving the above PDL data, the tag output unit 1002 of the controller 1000 generates a tag corresponding to the line width or character size for each 1200 dpi pixel, and outputs it to the resolution conversion unit 1012 of the image processing unit 1010. The resolution conversion unit 1012 of the image processing unit 1010 expands the tag output from the tag output unit 1002 to 2400 dpi, and outputs this to the selection unit 1014. The selection unit 1014 selects a raster image having an appropriate thinning amount from the raster image stored in the image memory 1030 described above for each pixel of 2400 dpi based on the tag expanded to 2400 dpi, and controls the selection result. Output to the unit 1020. Receiving the selection result of the selection unit 1014, the control unit 1020 sends the selected raster image to the image forming unit 1060, and the image forming unit 1060 performs image forming processing based on the sent raster image.

  In this way, a raster image that has been thinned twice is printed in a region where the input line width is 84.66 μm or more, and a thinning process is performed once in a region where the input line width is less than 84.66 μm. The performed raster image is printed. For this reason, in a region where the input line width is large, sufficient thinning is performed so as to prevent an increase in the output line width due to the characteristics of the image forming apparatus. On the other hand, in a region where the input line width is thin, the image is lost or blurred. The amount of thinning is suppressed to prevent. That is, printing with high reproducibility is performed on an original image having any input line width.

[B. Second embodiment]
Next, the image forming apparatus 1 according to the second embodiment of the present invention will be described. Hereinafter, the same reference numerals are assigned to configurations common to the first embodiment, and description thereof is omitted.
[B-1. Constitution]
FIG. 5 is a block diagram illustrating an electrical configuration of the image forming apparatus 1 according to the second embodiment.
The rasterization unit 1001 of the controller 1000 is a raster image generation unit similar to the rasterization unit 1001 of the first embodiment, but generates based on the PDL data received from the external PC 2 and outputs it to the acquisition unit 1019 of the image processing unit 1010. It differs from the rasterizing unit 1001 of the first embodiment in that the resolution of the raster image is 600 dpi. In the image forming apparatus 1 according to the second embodiment, the image processing unit 1010 includes a smoothing processing unit 1011. The smoothing processing unit 1011 has a pattern storage unit 10111. The pattern storage unit 10111 stores a correspondence relationship between a predetermined arrangement pattern of a plurality of pixels and a raster image of 2400 dpi, which is a resolution higher than the resolution of the raster image acquired by the acquisition unit 1019. It is. The minimum unit of the raster image stored in the pattern storage unit 10111 is one pixel of 2400 dpi. Then, the smoothing processing unit 1011 inspects the 600 dpi raster image described above for each pixel, and extracts a pattern in which the combination of these pixels and the surrounding pixels matches from the pattern stored in the pattern storage unit 10111 described above. Then, the pixel is replaced with a raster image corresponding to the extracted pattern, and then output to the image memory 1030. That is, the smoothing processing unit 1011 collates the arrangement pattern of each pixel of the raster image acquired by the acquisition unit 1019 and its surrounding pixels with the arrangement pattern stored in the correspondence storage unit, and uses this raster image. The replacement means replaces the raster image associated with the arrangement pattern matching the raster image.

[B-2. Operation]
Next, the operation of the image forming apparatus 1 in the second embodiment will be described.
FIG. 6 is a diagram illustrating a processing flow of the image forming apparatus 1 according to the second embodiment. As described above, the image forming apparatus 1 according to the second embodiment performs rasterization at 600 dpi. In addition, the image forming apparatus 1 according to the second embodiment performs a smoothing process on the 600 dpi raster image output from the rasterization unit 1001 of the controller 1000 instead of the resolution conversion according to the first embodiment.

  Here, the smoothing process will be described. The smoothing processing unit 1011 described above receives the 600 dpi raster image output by the rasterizing unit 1001 of the controller 1000. Then, the smoothing processing unit 1011 inspects this raster image for each pixel, extracts a pattern in which the combination of these pixels and the surrounding pixels is matched from the pattern stored in the pattern storage unit 10111, and outputs the pixel. Is replaced with a raster image corresponding to the extracted pattern, and then output to the image memory 1030.

  FIG. 7A is a diagram showing an example of the 600 dpi raster image. As shown in this figure, a hatched image having a width of one pixel of 600 dpi is converted into a raster image in which black pixels are in contact with each other only at their vertices by a rasterizing unit 1001 of the controller 1000. On the other hand, FIG. 7B is a diagram illustrating an example of a pattern stored in the pattern storage unit 10111 of the smoothing processing unit 1011. FIG. 7C shows a 2400 dpi raster image stored in association with each other in the pattern and pattern storage unit 10111 shown in FIG. The grid of FIG. 7B shows a pixel of 600 dpi, the center is a pixel of interest, 0 is a white pixel, 1 is a black pixel, and X is a pixel that may be a white pixel or a black pixel. Show. The smoothing processing unit 1011 inspects each pixel included in the raster image described above, and if 3 pixels × 3 pixels centered on the inspected pixel match a pattern as shown in FIG. The raster image is replaced with a 4 × 4 pixel raster image at 2400 dpi shown in FIG.

  In this way, the smoothing processing by the smoothing processing unit 1011 is performed, so that the raster image in FIG. 7A is converted into a raster image as shown in FIG. In FIG. 7D, the hatched portion is a portion different from the raster image of FIG. 7A, and indicates a black pixel. Since all the pixels of the raster image in FIG. 7A are replaced with a 2400 dpi raster image by the smoothing processing unit 1011, the minimum unit of the raster image shown in FIG. 7D is one pixel of 2400 dpi. .

  FIG. 8 is a diagram illustrating a relationship between the input line width and the output line width in the image forming apparatus 1 according to the second embodiment. FIG. 9 is a diagram showing the relationship between the input line width and the output density in the image forming apparatus 1 of the second embodiment. As shown in the figure, by changing the number of thinning processes according to the input line width, in electrophotographic printing, even if the image data to be printed has any input line width, the offset An output line width and output density substantially equal to printing can be obtained, and printing with high reproducibility can be performed.

[C. Modified example]
The embodiment described above may be modified as in the following example. Moreover, you may combine these modifications suitably.
(Modification 1) In the above-described embodiment, the relationship between the amount of light used for exposure in the latent image forming unit of the image forming unit and the thinning amount of the raster image selected by the image processing unit is not particularly mentioned. When the thinning amount in the raster image selected by the image processing unit is large, the latent image forming unit of the image forming unit reduces the amount of light when exposing the surface of the photosensitive drum, and the thinning amount is small. Alternatively, the amount of light when exposing the surface of the photosensitive drum may be increased. In this case, for example, the image forming unit may receive the tag used in the image processing unit together with the raster image from the image processing unit, and adjust the output intensity (light quantity) of the image forming unit according to the type of the tag. .
FIG. 10 is a diagram showing a flow of processing of the image forming unit in the first modification. The image forming unit receives a 2400 dpi raster image from the image processing unit and also receives a tag from the image processing unit. This tag is analyzed by the light amount control unit of the image forming unit. Specifically, the light amount control unit stores a correspondence relationship between the type of tag and the light amount used for exposure in the latent image forming unit of the image forming unit. For example, if the light amount corresponding to the tag “1” is “1.4”, the light amount corresponding to the tag “2” is “1”. Then, the received tag is compared with this correspondence relationship, the light quantity corresponding to the tag is specified, and output to the power modulation unit. The power modulation unit modulates the light amount used for exposure for each pixel according to the light amount specified by the light amount control unit, and outputs the modulated light amount to the image forming unit. As a result, the image forming unit exposes the latent image forming unit with the amount of light modulated by the power modulation unit, and an image is formed.
In this way, for the image data with a narrow input line width, even if the image processing unit reduces the number of thinning processes and the output density is reduced, the amount of light is increased. Highly reproducible printing can be performed.

  In the above-described aspect, the same tag as the tag indicating the number of times of the thinning process is used for light amount adjustment, but another tag may be used. For example, the tag output unit 1002 of the controller 1000 includes, in addition to the tag table in which the correspondence between the number of thinning processes and the conditions is described in the table storage unit 10021, the amount of light modulated by the power modulation unit and the conditions A tag table in which the correspondence is described is stored. The tag output unit 1002 includes a tag that specifies the number of thinning processes for each pixel (hereinafter referred to as a thinning process tag) and a tag that specifies the amount of light to be modulated by the power modulation unit for each pixel (hereinafter referred to as a light amount). Are output to the resolution converter. The resolution conversion unit converts the resolution of each of these tags. Then, the resolution-converted thinning processing tag is output to the selector of the image processing unit, and the resolution-converted light amount designation tag is output to the image forming unit. In this case, for example, 84.66 μm is adopted as the line width threshold value for switching the number of thinning processes, and the above threshold value is used as the line width threshold value for switching the amount of light modulated by the power modulation unit. A different 42.33 μm can be employed. That is, the number of thinning processes and the amount of light modulated by the power modulation unit can be adjusted separately using different threshold values.

(Modification 2) In the first embodiment described above, the resolution conversion is performed before the thinning process. However, the thinning process may be performed before the resolution conversion.
FIG. 11 is a diagram showing a flow of processing of the image processing unit in the second modification. In FIG. 11, the difference from FIG. 4 is that the 1200 dpi raster image output from the rasterization unit 1001 of the controller 1000 is thinned in addition to the flow of the thinning process after first converting the resolution. After that, there is a flow of processing for converting the resolution. As described above, the thinning process refers to inspecting a raster image for each pixel and replacing the pixel with a background pixel when a pixel group including a plurality of pixels including the pixel satisfies a predetermined condition. In this process, the image is thinned. When the thinning process is performed after the resolution conversion for converting the 1200 dpi raster image to the 2400 dpi raster image first, for example, a line with a width of one pixel to be deleted by the thinning process is equivalent to one pixel at 2400 dpi. Is a line of width. On the other hand, when the thinning process is performed prior to the resolution conversion, the line with a width of one pixel deleted by the thinning process has a width of one pixel at 1200 dpi, so that when converted to 2400 dpi, 2 lines are obtained. It has a width for pixels. Therefore, if the thinning process is performed prior to the resolution conversion, the thinning corresponding to two times when the thinning process is performed after the resolution conversion is performed.
In this way, since the thinning process can be performed with the resolution of the raster image output from the controller, that is, with a relatively low resolution, the processing scale such as the required memory and the number of processing steps can be reduced.

(Modification 3) In the embodiment described above, the tag output unit 1002 of the controller 1000 extracts information on the line width and the character size from the PDL data, and refers to the tag table stored in the table storage unit 10021. Although a tag corresponding to the extracted information is generated and output to the image processing unit 1010, the tag is not limited to the controller 1000. For example, a tag may be generated on the image processing unit 1010 side.
FIG. 12 is a block diagram showing an electrical configuration of the image forming apparatus 1 according to the third modification. 12 differs from FIG. 2 in that the controller 1000 does not have the tag output unit 1002 and the image processing unit 1010 has the tag generation unit 1015. The tag generation unit 1015 of the image processing unit 1010 includes a fine line pattern storage unit 10151, and a plurality of fine line patterns are stored in the fine line pattern storage unit 10151 (details will be described later).

  FIG. 13 is a diagram illustrating a processing flow of the image forming apparatus 1 according to the third modification. As shown in this figure, only a 1200 dpi raster image is output from the controller 1000 to the image processing unit 1010, and no tag is output. This raster image is acquired by the acquisition unit 1019 of the image processing unit 1010, as in the second modification shown in FIG. 11, and first the resolution conversion and then the thinning process, and the thinning process and the resolution conversion are performed. The processing to be performed is performed in parallel. At the same time, the tag generation unit 1015 described above generates a tag by performing turn matching processing on the raster image with reference to the fine line pattern stored in the fine line pattern storage unit 10151.

  FIG. 14 shows a pattern for detecting a 1200 dpi thin line. 14A to 14M are all windows having a window size = 3, and this grid is the size of the resolution of the raster image output from the controller 1000. FIG. That is, in this embodiment, the grid represents 1200 dpi. The tag generation unit 1015 inspects this raster image for each pixel, and if the relationship between the pixel of interest and the surrounding pixels matches one of the patterns shown in FIGS. The tag for is stored as “1”. On the other hand, when the relationship between the pixel (target pixel) inspected by the tag generation unit 1015 and the surrounding pixels does not match any of the patterns in FIGS. 14A to 14M, the tag generation unit 1015 Match with the next pattern.

  FIG. 15 shows a pattern for detecting a 600 dpi thin line. FIGS. 15A to 15D are all windows having a window size = 5, and this grid is the size of the resolution of the raster image output from the controller 1000. The tag generation unit 1015 compares pixels that do not match any of the patterns shown in FIG. 14 with the patterns shown in FIGS. Here, in FIG. 15, a lattice whose inside is white indicates a white pixel, and a lattice which is black indicates a black pixel. A grid having “X” drawn therein indicates pixels that may be either black or white. These patterns show a pattern in which two adjacent black pixels are sandwiched between at least one white pixel, and there is a thin line width of two pixels at 1200 dpi, that is, a width of one pixel at 600 dpi. Show. The tag generation unit 1015 stores the tag for the pixel as “1” when the relationship between the pixel of interest and the surrounding pixels matches one of the patterns in FIGS. On the other hand, if the relationship between the pixel (target pixel) inspected by the tag generator 1015 and the surrounding pixels does not match any of the patterns in FIGS. Store as “2”. That is, the tag generation unit 1015 determines whether or not the pixels included in the raster image depend on whether or not a pixel group including each pixel included in the raster image acquired by the acquisition unit 1019 and its surrounding pixels satisfies a predetermined condition. This is designation information generation means for generating designation information for designating the thinning amount for each line.

Returning to FIG. 13, the description will be continued. In this way, when a tag is generated for each 1200 dpi pixel by the tag generation unit 1015, this tag is converted to 2400 dpi by the resolution conversion unit and output to the selection unit 1014. The selection unit 1014 selects a raster image with an appropriate thinning amount for each pixel from the raster images thinned by the thinning processing unit 1013 according to the received tag, and the selection result is controlled by the control unit 1020. Output to.
In this way, even if the conventional controller is used as it is for the image processing unit, the image processing unit appropriately analyzes and extracts the thin line from the PDL data, so that appropriate thinning can be performed for any input line width. An amount can be selected to form an image.
In the third modification, the data received by the controller 1000 may not be PDL data. For example, a raster image output by another device may be received and the raster image may be output. In short, the controller 1000 only needs to output a raster image. In the controller 1000 of the second embodiment, the input data may not be PDL data as long as a raster image having the same resolution as that used in the smoothing process is output. For example, the controller 1000 automatically detects input data. If the data is PDL data, the controller 1000 performs the above-described rasterization. If the data is a raster image, the controller 1000 performs resolution conversion as necessary to obtain a raster having a predetermined resolution. Generate and output an image.

(Modification 4) In the above-described embodiment, the rasterization unit 1001 of the controller 1000 rasterizes the PDL data received from the external PC 2. However, these controllers may receive PDL data from other than the external PC 2. For example, PDL data may be received from an image reading apparatus that reads an original image and outputs PDL data.

(Modification 5) Further, in the above-described embodiment, the image forming apparatus 1 uses the Hiditch thinning algorithm in the thinning process, but other thinning algorithms may be used. For example, the contraction algorithm described above may be used.
In particular, a thinning algorithm that performs thinning with a window size = 3 is desirable because it can minimize the computational resources such as the amount of memory and the number of steps required for processing.

(Modification 6) In the above-described embodiment, the number of times the thinning process is performed, that is, the thinning amount is either “1” or “2”. “0” not to be performed may be selected. In this case, for example, it is as follows. The image memory 1030 stores a raster image that has not been thinned at all (that is, a thinning amount of “0”) as well as raster images of the thinning amounts “1” and “2”. In the tag table of the table storage unit 10021, the condition for the tag “0” is described. Here, when the line width or character size of a certain area described in the PDL data matches this condition, the tag output unit 1002 of the controller 1000 outputs a tag of “0” for the area. The selection unit 1014 that has received the selection selects the raster image having the thinning amount “0” as shown by the one-dot chain line in FIG.

1 is a diagram illustrating a structure of an image forming apparatus according to a first embodiment. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus. FIG. It is a figure which shows an example of the tag table memorize | stored in the table memory | storage part. FIG. 6 is a diagram illustrating a processing flow of the image forming apparatus. It is a block diagram which shows the electric constitution of the image forming apparatus in 2nd embodiment. It is a figure which shows the flow of a process of the image forming apparatus in 2nd embodiment. It is a figure for demonstrating an example of the 600 dpi raster image in 2nd embodiment, and the smoothing process performed with respect to this. It is a figure which shows the relationship between the input line width and output line width in the image forming apparatus of 2nd embodiment. It is a figure which shows the relationship between the input line | wire width and output density in the image forming apparatus of 2nd embodiment. FIG. 10 is a diagram illustrating a processing flow of an image forming unit in Modification 1. It is a figure which shows the flow of a process of the image process part in the modification 2. FIG. 10 is a block diagram illustrating an electrical configuration of an image forming apparatus according to Modification 3. FIG. 10 is a diagram illustrating a processing flow of an image forming apparatus according to a third modification. This is a pattern for detecting a 1200 dpi thin line. This is a pattern for detecting a 600 dpi thin line. FIG. 5 is a flowchart showing an example of a thinning process in the image forming apparatus previously invented by the inventors of the present invention. It is a figure for demonstrating the window used for a thinning process, and the method of a thinning process. It is the figure which showed the relationship between the input line width and the output line width in the conventional thinning process for every frequency | count of thinning process. It is the figure which showed the relationship between the input line width and output density in the conventional thinning process for every frequency | count of thinning process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 1000 ... Controller, 1001 ... Rasterize part, 1002 ... Tag output part, 10021 ... Table storage part, 1010 ... Image processing part, 1011 ... Smoothing processing part, 10111 ... Pattern storage part, 1012 ... Resolution conversion part DESCRIPTION OF SYMBOLS 1013 ... Thinning process part, 1014 ... Selection part, 1015 ... Tag production | generation part, 10151 ... Fine line pattern memory | storage part, 1020 ... Control part, 1030 ... Image memory, 1040 ... Operation part, 1050 ... Display part, 1060 ... Image formation , 12: Paper storage unit, 14 ... Transfer unit, 141 ... Intermediate transfer belt, 142 ... Secondary transfer roll, 143 ... Opposing roll, 15 ... Fixing unit, 151 ... Heating roll, 152 ... Pressure roll, 153 ... Peeling Members, 154... Guide, 19.

Claims (9)

Raster image acquisition means for acquiring a raster image which is image data expressed in a raster format;
Raster image generation means for generating a plurality of raster images having different thinning amounts using the raster image acquired by the raster image acquisition means;
Designation information obtaining means for obtaining designation information for designating a thinning amount for each pixel included in the raster image obtained by the raster image obtaining means;
Image formation in which a raster image corresponding to the thinning amount designated by the obtained designation information is selected for each pixel from a plurality of raster images generated by the raster image generation means, and an image is formed based on the raster image An image processing apparatus comprising: selection means for outputting the selected raster image to the means. Raster image acquisition means for acquiring a raster image which is image data expressed in a raster format;
Raster image generation means for generating a plurality of raster images having different thinning amounts using the raster image acquired by the raster image acquisition means;
Depending on whether or not a pixel group consisting of each pixel included in the raster image acquired by the raster image acquisition unit and its surrounding pixels satisfies a predetermined condition, the thinning amount is set for each pixel included in the raster image. Designated information generating means for generating specified information to be specified;
Image formation in which a raster image corresponding to a thinning amount specified by the generated specification information is selected for each pixel from a plurality of raster images generated by the raster image generation means, and an image is formed based on the raster image An image processing apparatus comprising: selection means for outputting the selected raster image to the means. The raster image generating means includes
Resolution conversion means for converting the raster image acquired by the raster image acquisition means into a raster image having a resolution higher than the resolution of the raster image;
When a pixel group consisting of each pixel included in the raster image obtained by the conversion of the resolution conversion unit and its surrounding pixels satisfies a predetermined condition, the pixel is replaced with a pixel of a different color. First thinning means for thinning an image;
When a pixel group consisting of each pixel included in the raster image thinned by the first thinning means and its surrounding pixels satisfies a predetermined condition, the pixel is replaced with a pixel of a different color. The image processing apparatus according to claim 1, further comprising: a second thinning unit configured to thin the image. The raster image generating means includes
A group of pixels formed by converting the raster image acquired by the raster image acquisition means into a raster image having a resolution higher than the resolution of the raster image, and each pixel included in the converted raster image and its surrounding pixels Is included in the raster image acquired by the first thinning means for thinning the image by replacing each pixel with a pixel of a different color and the raster image acquisition means. When a pixel group consisting of each pixel and its surrounding pixels satisfies a predetermined condition, the pixel is thinned by replacing each pixel with a pixel of a different color, and the thinned raster image is And a second thinning means for converting the raster image into a raster image having a higher resolution than that of the raster image. The image processing apparatus according to 2. The raster image generating means includes
Correspondence relationship storage means for storing a correspondence relationship between an arrangement pattern of a plurality of pixels and a raster image having a resolution higher than the resolution of the raster image acquired by the raster image acquisition means;
The arrangement pattern of each pixel of the raster image acquired by the raster image acquisition unit and its surrounding pixels is compared with the arrangement pattern stored in the correspondence storage unit, and the acquired raster image is Replacement means for replacing with a raster image associated with the arrangement pattern matching the raster image;
When a pixel group consisting of each pixel included in the raster image replaced by the replacement unit and its surrounding pixels satisfies a predetermined condition, each pixel is replaced with a pixel of a different color. First thinning means for thinning;
If a pixel group consisting of each pixel included in the raster image replaced by the first thinning means and its surrounding pixels satisfies a predetermined condition, each pixel is replaced with a pixel of a different color. The image processing apparatus according to claim 1, further comprising: a second thinning unit that thins the image. The pixel group when the first thinning unit and the second thinning unit perform thinning includes a pixel group of 3 rows and 3 columns, which includes the pixels and peripheral pixels surrounding the pixel. The image processing apparatus according to claim 3, wherein the image processing apparatus is an image processing apparatus. An image processing apparatus according to any one of claims 1 to 6,
An image forming apparatus comprising: an image forming unit that forms an image based on a raster image output from the selection unit of the image processing apparatus. The image forming means includes:
An image carrier,
Charging means for charging the surface of the image carrier;
A latent image forming means for exposing the surface of the image carrier charged by the charging means to form a latent image;
Developing means for supplying a developer to the surface of the image carrier on which the latent image is formed to develop the latent image;
Transfer means for transferring the image obtained by the development to a recording medium,
The latent image forming means includes:
When the thinning amount in the raster image selected by the selection means is large, the light amount when exposing the surface of the image carrier is reduced, and when the thinning amount in the raster image selected by the selection means is small The image forming apparatus according to claim 7, wherein the amount of light when exposing the surface of the image carrier is increased. An image processing apparatus according to claim 1;
Description data describing the contents of an image is analyzed to generate the raster image and the designation information, the raster image data is supplied to the raster image acquisition means of the image processing apparatus, and the designation information is acquired from the designation information. Supply means for supplying means;
An image forming apparatus comprising: an image forming unit that forms an image based on a raster image output from the selection unit of the image processing apparatus.

Images