JP2013026991A - Image processing device, image forming device, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing device, an image forming device, and a program capable of smoothly printing an edge part of a thin line whose line width is less than or equal to a fixed number of dots when printing image data including the thin line.SOLUTION: An edge detection unit 41 detects whether a target pixel is a pixel constituting an edge part using an edge detection filter. An edge detection unit 42 detects whether the target pixel is the pixel constituting the edge part by pattern matching. A line width detection unit 50 detects a line width of pixels in the edge part detected by the edge detection unit 42. A gradation correction unit 43 performs smoothing processing by performing, for example, gradation correction for screen processing with 600 lines with respect to pixels in the edge part. A pattern changing unit 44 performs smoothing processing by changing an arrangement pattern of pixels around the pixels in the edge part. When a detected line width is less than or equal to 2 dots, a selection unit 46 selects pixel data of the arrangement pattern changed by the pattern changing unit 44 in preference to other data.

Description

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

  In Patent Document 1, edge detection processing by the edge detection filter method is performed for halftone character / line drawing data, and edge detection processing by pattern matching is performed for character / line drawing data having a density value of 100%. A technique for performing a smoothing process is disclosed.

  Patent Document 2 discloses an image processing apparatus in which an edge portion detected by pattern matching is replaced with a thinned pattern as a countermeasure against line thickening in an electrophotographic system.

JP-A-8-23446 JP-A-7-334672

  An object of the present invention is to print image data that includes fine lines with a line width equal to or less than a certain number of dots, and capable of smoothly printing edge portions of fine lines as compared to the case without this configuration. A processing apparatus, an image forming apparatus, and a program are provided.

[Image processing device]
The present invention according to claim 1 is a pixel in which the target pixel constitutes an edge portion by performing a preset operation on the pixel values of the pixels around the target pixel on the input image data. First edge detection means for detecting whether there is,
By detecting whether or not a pixel arrangement pattern around the pixel of interest matches a preset pixel arrangement pattern, it is detected whether or not the pixel of interest is a pixel constituting an edge portion. Edge detection means;
Edge width detection means for detecting an edge width, which is the width of the edge portion, of the pixels of the edge portion detected by the second edge detection means;
Gradation correction means for performing gradation correction for performing screen processing with a higher number of lines than the non-edge portion on the pixels of the edge portion detected by the first edge detection means;
Screen processing means for performing screen processing with a higher number of lines than the non-edge portion on the pixel data after the gradation correction is performed by the gradation correction means;
Pattern changing means for changing the arrangement pattern of the pixels of the edge portion detected by the second edge detection means and the pixels around the pixel into a pixel arrangement pattern for smoothing the edge portion;
When the edge width detected by the edge width detecting means is narrower than a preset value, the pattern changing means is more than pixel data subjected to screen processing with a higher number of lines than the non-edge portion by the screen processing means. And an image processing apparatus having selection means for preferentially selecting pixel data whose array pattern has been changed.

  According to the second aspect of the present invention, in the case where the selection unit has the edge width detected by the edge width detection unit wider than a preset value, the pixel whose array pattern has been changed by the pattern change unit 2. The image processing apparatus according to claim 1, wherein pixel data that has undergone screen processing with a higher number of lines than the non-edge portion is preferentially selected by the screen processing means over data.

  According to a third aspect of the present invention, the edge width detection means sequentially selects one of the pixels constituting the image data as a target pixel, and a pixel having a pixel value substantially the same as the target pixel is the target pixel. The image processing apparatus according to claim 1, wherein the number of pixels that are continuous from the pixel in the horizontal direction or the vertical direction is detected as an edge width.

  According to a fourth aspect of the present invention, in the first aspect, the gradation correction unit performs gradation correction so as to decrease the pixel value of the edge portion pixel when the thinning process is designated. An image processing apparatus according to item 1.

  According to the fifth aspect of the present invention, when the thinning process is designated, the pattern changing unit smoothes the edge portion and thins the arrangement pattern of the pixels in the edge portion and the pixels around the pixel. 5. The image processing apparatus according to claim 1, wherein the image processing apparatus is changed to a pixel array pattern.

[Image forming apparatus]
The present invention according to claim 6 is a pixel in which the target pixel constitutes an edge portion by performing a preset operation on the pixel values of the pixels around the target pixel for the input image data. First edge detection means for detecting whether there is,
By detecting whether or not a pixel arrangement pattern around the pixel of interest matches a preset pixel arrangement pattern, it is detected whether or not the pixel of interest is a pixel constituting an edge portion. Edge detection means;
Edge width detection means for detecting an edge width, which is the width of the edge portion, of the pixels of the edge portion detected by the second edge detection means;
Gradation correction means for performing gradation correction for performing screen processing with a higher number of lines than the non-edge portion on the pixels of the edge portion detected by the first edge detection means;
Screen processing means for performing screen processing with a higher number of lines than the non-edge portion on the pixel data after the gradation correction is performed by the gradation correction means;
Pattern changing means for changing the arrangement pattern of the pixels of the edge portion detected by the second edge detection means and the pixels around the pixel into a pixel arrangement pattern for smoothing the edge portion;
When the edge width detected by the edge width detecting means is narrower than a preset value, the pattern changing means is more than pixel data subjected to screen processing with a higher number of lines than the non-edge portion by the screen processing means. Selection means for preferentially selecting pixel data whose array pattern has been changed by:
And an image output unit that outputs an image based on the pixel data selected by the selection unit.

[program]
According to the seventh aspect of the present invention, by performing a predetermined calculation on the pixel values of the pixels around the target pixel for the input image data, the target pixel is a pixel constituting the edge portion. A first edge detecting step for detecting whether or not there is;
By detecting whether or not a pixel arrangement pattern around the pixel of interest matches a preset pixel arrangement pattern, it is detected whether or not the pixel of interest is a pixel constituting an edge portion. An edge detection step;
An edge width detecting step for detecting an edge width which is a width of the edge portion of the pixel of the edge portion detected in the second edge detecting step;
Performing gradation correction for performing screen processing with a higher number of lines than the non-edge portion on the edge portion pixels detected in the first edge detection step;
A step of performing screen processing with a higher number of lines than the non-edge portion on the pixel data after the gradation correction is performed;
Changing the arrangement pattern of the pixels of the edge portion detected in the second edge detection step and the pixels around the pixel to a pixel arrangement pattern for smoothing the edge portion; and
If the edge width detected in the edge width detection step is narrower than a preset value, the pixel whose array pattern has been changed from the pixel data subjected to screen processing with a higher number of lines than the non-edge portion A program for causing a computer to execute a step of preferentially selecting data.

  According to the first aspect of the present invention, when printing image data including a thin line having a line width equal to or less than a certain number of dots, the edge portion of the fine line is printed more smoothly than when the image data is not provided. It is possible to provide an image processing apparatus that can perform the above processing.

  According to the second aspect of the present invention, in addition to the effect obtained by the first aspect of the present invention, it is possible to provide an image processing apparatus that can reduce the number of arrangement patterns prepared in advance. it can.

  According to the third aspect of the present invention, in addition to the effect obtained by the first or second aspect of the present invention, it is possible to provide an image processing apparatus capable of easily detecting the edge width.

  According to the present invention of claim 4, in addition to the effect obtained by the invention of any one of claims 1 to 3, the edge portion detected by the first edge detecting means is thinned. It is possible to provide an image processing apparatus that can

  According to the present invention of claim 5, in addition to the effect obtained by the invention of any one of claims 1 to 4, the edge portion detected by the second edge detection means is thinned. It is possible to provide an image processing apparatus that can

  According to the sixth aspect of the present invention, when printing image data including a thin line having a line width equal to or less than a certain number of dots, the edge portion of the fine line is printed more smoothly than when the image data is not provided. It is possible to provide an image forming apparatus capable of performing the above.

  According to the seventh aspect of the present invention, when printing image data including a thin line having a line width equal to or less than a certain number of dots, the edge portion of the fine line is printed more smoothly than when the present configuration is not provided. Can be provided.

It is a figure which shows the system configuration | structure of the image processing apparatus of one Embodiment of this invention. It is a block diagram which shows the hardware constitutions of the image processing apparatus 10 in one Embodiment of this invention. It is a block diagram which shows the function structure of the image processing apparatus 10 in one Embodiment of this invention. FIG. 4 is a block diagram illustrating a configuration of the image processing device 521 illustrated in FIG. 3. It is a figure for demonstrating the detail of the edge detection process in the edge detection part 41 shown in FIG. It is a figure which shows an example of the image data before thinning processing in the gradation correction | amendment part 43 is performed. It is a figure which shows the theoretical cross section at the time of outputting an image on printing paper based on the image data shown in FIG. It is a figure which shows the actual condition at the time of outputting an image on a printing paper based on the image data shown in FIG. It is a figure which shows an example of the image data in which the thinning process was performed in the gradation correction | amendment part. It is a figure which shows the theoretical cross section at the time of outputting an image on printing paper based on the image data shown in FIG. It is a figure which shows the actual condition at the time of outputting an image on a printing paper based on the image data shown in FIG. It is a figure which shows an example of the matching pattern (array pattern) set in the edge detection part. It is a figure which shows an example of the image data detected by the matching pattern shown in FIG. It is a figure which shows an example of the replacement pattern for performing the smoothing process for smoothing an edge part. It is a figure which shows an example of the replacement pattern for performing the smoothing process for smoothing an edge part, and thinning. It is a figure which shows the determination window of 5x5 pixel used in a line | wire width detection process. It is a table | surface which shows the conditions for determining a 1 and 2 dot positive thin line. It is a figure for demonstrating the setting of the selection control in the selection part.

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

  FIG. 1 is a block diagram showing a configuration of an image forming system according to an embodiment of the present invention.

  As shown in FIG. 1, the image forming system according to an embodiment of the present invention includes an image forming apparatus 10 and a terminal device 20 connected to each other via a network 30. The terminal device 20 generates print data and transmits the print data generated via the network 30 to the image forming apparatus 10. The image forming apparatus 10 receives the print data transmitted from the terminal device 20 and outputs an image corresponding to the print data on a sheet. The image forming apparatus 10 is an apparatus called a so-called multi-function machine having a plurality of functions such as a print function, a scan function, a copy function, and a facsimile function.

  Next, FIG. 2 shows a hardware configuration of the image forming apparatus 10 in the image forming system of the present embodiment.

  As shown in FIG. 2, the image forming apparatus 10 transmits and receives data to and from an external device or the like via a CPU 11, a memory 12, a storage device 13 such as a hard disk drive (HDD), and a network 30. A communication interface (IF) 14, a touch panel or liquid crystal display, and a user interface (UI) device 15 including a keyboard, a scanner 16, and a print engine 17 are included. These components are connected to each other via a control bus 18.

  The CPU 11 executes predetermined processing based on a control program stored in the memory 12 or the storage device 13 and controls the operation of the image forming apparatus 10. In the present embodiment, the CPU 11 has been described as reading and executing a control program stored in the memory 12 or the storage device 13, but the program is stored in a storage medium such as a CD-ROM and stored in the CPU 11. It is also possible to provide.

  FIG. 3 is a block diagram showing a functional configuration of the image forming apparatus 10 realized by executing the control program.

  As illustrated in FIG. 3, the image forming apparatus 10 according to the present exemplary embodiment includes a controller 51, a print engine control unit 52, and a print engine 17.

  The controller 51 includes a PDL (Page Description Language) interpreting unit 511, a drawing unit 512, and a rendering unit 513.

  Further, the print engine control unit 52 includes an image processing device 521 and a modulation unit 522.

  The PDL interpretation unit 511 receives the PDL data from the terminal device 20, and interprets the drawing object described by the PDL data.

  The drawing unit 512 performs drawing processing for each drawing object interpreted by the PDL interpretation unit 511 to generate an intermediate code, or a color signal used by the printer engine 17 from a color signal (RGB) designated in the PDL. Processing such as conversion to (YMCK) is performed.

  The rendering unit 513 performs rendering processing for generating bitmap data for each YMCK that can be printed by the printer engine 17 based on the intermediate data generated by the drawing unit 512.

  The image processing unit 521 performs various types of image processing such as edge portion smoothing processing, thinning processing, and screen processing on the bitmap data (image data) generated by the controller 51.

  The modulation unit 522 generates a pulse signal for printing image data by performing modulation processing based on the image data after the screen processing is performed in the image processing unit 521.

  In the print engine 17, the laser is controlled based on the pulse signal generated by the modulation unit 522, so that an image based on the image data after the image processing is performed by the image processing unit 521 is output on the printing paper. Is done.

Next, details of the image processing apparatus 521 shown in FIG. 3 will be described with reference to the block diagram of FIG.
As shown in FIG. 4, the image processing apparatus 521 includes edge detection units 41 and 42, a gradation correction unit 43, a pattern change unit 44, a screen processing unit 45, and a selection unit 46. A line width detection unit 50 is provided in the edge detection unit 42.

  The edge detection unit 41 (edge detection filter) performs a predetermined calculation on the pixel values of the pixels around the target pixel with respect to the input image data, so that the target pixel forms an edge part. Whether it is a pixel is detected.

  The edge detection unit (pattern matching) 42 determines whether the pixel arrangement pattern around the pixel of interest matches a pixel arrangement pattern set in advance, so that the pixel of interest constitutes the edge portion. Detect whether or not there is.

  The line width (edge width) detection unit 50 detects the line width (edge width) which is the width of the edge portion of the pixel of the edge portion detected by the edge detection unit 42. Note that the line width detection unit 50 sequentially selects one of the pixels constituting the image data as a target pixel, and pixels having pixel values substantially the same as the target pixel continue in the horizontal direction or the vertical direction from the target pixel. The number of pixels to be detected is detected as the line width.

  The edge detection results in the edge detection units 41 and 42 and the line width detection result by the line width detection unit 50 are transferred to the selection unit 46.

  Details of the edge detection processing in the edge detection units 41 and 42 and the line width detection processing by the line width detection unit 50 will be described later.

  The gradation correction unit 43 performs gradation correction for performing screen processing with a higher number of lines, for example, 600 lines, than the non-edge part on the pixels of the edge part detected by the edge detection unit 41. Perform smoothing processing. Here, the number of lines indicates a dot arrangement density in screen processing. Further, when the thinning process is designated, the gradation correction unit 43 performs gradation correction so as to decrease the pixel value of the edge portion pixel. The thinning process in the gradation correction unit 43 will also be described later.

  The pattern changing unit 44 performs the smoothing process by changing the arrangement pattern of the pixels in the edge portion detected by the edge detection unit 42 and the pixels around the pixels to a pixel arrangement pattern for smoothing the edge portion. Further, when the thinning process is designated, the pattern changing unit 44 changes the arrangement pattern of the pixels in the edge portion and the pixels around the pixel to a pixel arrangement pattern for smoothing the edge portion and performing thinning. To do. The pattern changing process in the pattern changing unit 44 will also be described later.

  The screen processing unit 45 performs screen processing with a higher number of lines, for example, 600 lines, than the non-edge portion on the pixel data after the gradation correction is performed by the gradation correction unit 43 to generate a pseudo halftone image. Generate. The screen processing unit 45 performs screen processing with 200 lines for pixels that are determined not to be edge portions in either of the edge detection units 41 and 42.

  When the edge width detected by the edge width detection unit 50 is narrower than 2 dots, the selection unit 46 uses the pattern change unit 44 to perform an array pattern rather than the pixel data subjected to screen processing at 600 lines by the screen processing unit 45. The pixel data that has been changed is preferentially selected.

  In addition, when the edge width detected by the edge width detection unit 50 is 3 dots or more, the selection unit 46 uses the 600 lines by the screen processing unit 45 rather than the pixel data whose array pattern has been changed by the pattern change unit 44. The pixel data subjected to the screen processing is preferentially selected.

  In this embodiment, the edge detection process and the screen process are performed by the print engine control unit 52. However, the edge detection process and the screen process may be performed by the rendering unit 513 in order to perform load distribution.

  Next, the operation of the image forming apparatus 10 of this embodiment will be described in detail with reference to the drawings.

  First, the details of the edge detection process in the edge detection unit 41 shown in FIG. 4 will be described with reference to FIG.

  The edge detection process shown in FIG. 5 is a detection method based on density difference determination using a 3 × 3 edge detection window. In this density difference determination method, a pixel P5 is set as a target pixel, and whether or not the target pixel P5 is an edge pixel based on the pixel values of eight pixels P1 to P4 and P6 to P9 around the target pixel P5 It is determined whether the pixel is a part of the pixel.

  Specifically, when the pixel values of the eight pixels P1 to P4 and P6 to P9 are expressed as P1 to P4 and P6 to P9, respectively, the values of SH, SV, SR, and SL are expressed by the equations shown in FIG. If the maximum value (Max (SH, SV, SR, SL)) of these values is equal to or greater than the edge threshold, the pixel of interest is an edge pixel, and if it is less than the edge threshold, the pixel of interest is a non-edge It is determined that the pixel is a partial pixel. The edge threshold is set to a value of 240, for example, when the pixel value of each pixel is expressed by 0 to 255.

  Next, the thinning process performed in the gradation correction unit 43 will be described with reference to FIGS.

  First, FIG. 6 shows image data before thinning processing is performed. In FIG. 6, the density value of each pixel is displayed in%. That is, the pixel described as “100” in FIG. 6 means that the density value is 100%.

  FIG. 7 and FIG. 8 show a state in which an image is output on printing paper based on such image data without performing the thinning process. FIG. 7 is a diagram showing a cross section of a theoretical image based on the image data shown in FIG. The arrows in FIG. 7 indicate the directions when the image is viewed from the front direction with respect to the printing paper. As shown in FIG. 7, if the toner is fixed on the printing paper, an image faithful to the image data can be obtained. However, when the toner is actually fixed on the printing paper, a situation occurs in which the edge portion expands as shown in FIG.

  Therefore, the gradation correction unit 43 performs the thinning process on the image data shown in FIG. 6 and changes the image data to that shown in FIG. That is, the tone correction unit 43 performs a thinning process that reduces the density value of a pixel having a density value of 100% at the edge part. In the example shown in FIG. 9, the density value of 100% is reduced to 40%.

  FIG. 10 and FIG. 11 show the situation when an image is output on the printing paper based on the image data shown in FIG. FIG. 10 is a diagram showing a cross section of a theoretical image based on the image data shown in FIG. Referring to FIG. 10, it can be seen that the density value of the pixel in the edge portion is lower than in the other portions. FIG. 11 shows a state in which an image is output on actual printing paper based on such image data. In FIG. 11, the edge portion is slightly expanded, but it can be seen that a result close to the image to be output in the original image data is obtained as compared with FIG. 8.

  Next, the pattern matching operation in the edge detection unit 42 shown in FIG. 4 and the pattern change operation in the pattern change unit 44 will be described with reference to FIGS.

  In the edge detection unit 42, for example, a matching pattern (array pattern) as shown in FIG. 12 is set in advance. The matching pattern shown in FIG. 12 is composed of 7 × 7 pixels centered on the target pixel. “0” means a white pixel, “1” means a black pixel, and “2”. Means that either pixel may be used.

  In the present embodiment, the edge detection unit 42 is described as performing input edge data detection and line width detection by converting input image data into a binary image. However, the edge detection unit 42 may perform edge detection and line width detection without performing binarization of the image data without changing the multivalued image data.

  Then, description will be made assuming that image data as shown in FIG. 13 is detected by the matching pattern of FIG. When matching processing between a matching pattern and image data is performed, it can be easily realized by calculating an exclusive OR of corresponding pixels.

  When a match between the matching pattern and the image data pattern is detected in this way, the pattern changing unit 44 replaces the detected pixel pattern of the image data with a pixel pattern as shown in FIG. 14 or FIG.

  The replacement pattern shown in FIG. 14 is an example of a replacement pattern for performing a smoothing process for smoothing the edge portion. Further, the replacement pattern shown in FIG. 15 is an example of a replacement pattern for performing smoothing processing for smoothing an edge portion and thinning.

  Next, line width (edge width) detection processing in the line width detection unit 50 shown in FIG. 4 will be described with reference to FIGS.

  In this line width detection process, a determination window of 5 × 5 pixels as shown in FIG. 16 is used. The reason for using this 5 × 5 pixel determination window is to detect a thin line having an edge width of up to 2 dots. That is, the size of the determination window varies depending on the line width to be detected. In this embodiment, a case where a positive thin line having a line width of 1 dot or 2 dots is detected will be described.

  The line width detection unit 50 sets the thirteenth pixel as a target pixel in the determination window of 5 columns × 5 rows as shown in FIG. 16, and if the determination condition as shown in FIG. The pixel is determined to be a pixel constituting a positive thin line.

  FIG. 17A is a table showing conditions for determining a 1-dot positive thin line, and FIG. 17B is a table showing conditions for determining a 2-dot positive thin line.

  In FIG. 17, for the sake of simplicity, for example, the pixel value of the thirteenth pixel is simply expressed as “13”, and the pixel value of the fourteenth pixel is simply expressed as “14”. . In the present embodiment, since the image data is described as being binarized in the edge detection unit 42, the pixel value of each pixel is either on or off.

  For example, as shown in FIG. 17B, the pixel value of the thirteenth pixel and the pixel value of the twelfth pixel that are the target pixel are both on (dot determination), and the pixel value of the eleventh pixel is 14 When the pixel values of the second pixel are both off (background determination), it is determined that the thirteenth pixel that is the target pixel is a pixel that forms a 2-dot positive thin line.

  Then, the selection unit 46 performs selection control by setting as shown in FIG. 18 based on the edge detection results (edge / non-edge) in the edge detection units 41 and 42 and the line width detection result in the line width detection unit 50, for example. Done.

  Specifically, when the detected line width (edge width) is 1 dot or 2 dots, the selection unit 46 selects the smoothing method based on the pattern matching method in preference to the smoothing method based on the edge detection filter method. That is, when the detected line width is 1 dot or 2 dots, the selection unit 46 performs smoothing processing by changing the pattern in the pattern changing unit 44 even when the edge detecting units 41 and 42 detect both edges. Is selected and output to the modulation unit 522.

  When the detected line width is 3 dots or more, the selection unit 46 selects the smoothing method based on the edge detection filter method in preference to the smoothing method based on the pattern matching method. That is, when the detected line width is 3 dots or more, the selection unit 46 performs gradation correction in the gradation correction unit 43 even when both edge portions are detected by the edge detection units 41 and 42. Then, the pixel value after the screen processing of 600 lines is performed in the screen processing unit 45 is selected and output to the modulation unit 522.

  The reason for preferentially selecting the smoothing method based on the pattern matching method when the detected line width is 2 dots or less will be described below.

  The edge detection method using the edge detection filter performed in the edge detection unit 41 has an advantage that edge portions in all directions can be detected. However, in the smoothing process performed by the gradation correction unit 43 performed thereafter, only the smoothing process of changing the number of lines in the screen process is performed. In addition, when thinning processing is performed, only thinning processing that reduces the pixel value of the edge portion can be performed.

  On the other hand, in the edge detection method and the smoothing process by the pattern matching method performed in the edge detection unit 42, the pixel arrangement pattern detected as the edge part is replaced with a pixel arrangement pattern prepared in advance, so that the accuracy is high. High smoothing processing and thinning processing are possible. However, in the edge detection method based on this pattern matching method, since the pixel arrangement patterns that can be prepared are limited, the detection direction is limited. Further, there is a problem that many pixel arrangement patterns must be prepared in order to detect edge portions of various shapes.

  For this reason, in the present embodiment, the fine line of 2 dots or less in which the roughness or fading of the edge portion is conspicuous is selected by giving priority to the smoothing method based on the high-precision pattern matching method, and the roughness or fading of the edge portion is not noticeable. For edge portions having a line width of 3 dots or more, the smoothing method based on the edge detection filter method is preferentially selected.

[Modification]
In the above embodiment, the case where the line width detected as a thin line is 1 dot or 2 dots has been described, but the present invention is not limited to this, and the line width detected as a thin line is set to another value. Even in this case, the present invention can be similarly applied.

10 Image forming apparatus 11 CPU
12 Memory 13 Storage Device 14 Communication Interface (IF)
DESCRIPTION OF SYMBOLS 15 User interface (UI) apparatus 16 Scanner 17 Print engine 18 Control bus 20 Terminal apparatus 30 Network 41 Edge detection part (edge detection filter)
42 Edge detector (pattern matching)
Reference Signs List 43 edge gradation correction unit 44 pattern change unit 45 screen processing unit 46 selection unit 50 line width detection unit 51 controller 52 print engine control unit 511 PDL interpretation unit 512 drawing unit 513 rendering unit 521 image processing device 522 modulation unit

Claims (7)

A first operation for detecting whether or not the pixel of interest is a pixel constituting an edge portion is performed by performing a preset operation on the pixel values of pixels around the pixel of interest on the input image data. Edge detection means,
By detecting whether or not a pixel arrangement pattern around the pixel of interest matches a preset pixel arrangement pattern, it is detected whether or not the pixel of interest is a pixel constituting an edge portion. Edge detection means;
Edge width detection means for detecting an edge width, which is the width of the edge portion, of the pixels of the edge portion detected by the second edge detection means;
Gradation correction means for performing gradation correction for performing screen processing with a higher number of lines than the non-edge portion on the pixels of the edge portion detected by the first edge detection means;
Screen processing means for performing screen processing with a higher number of lines than the non-edge portion on the pixel data after the gradation correction is performed by the gradation correction means;
Pattern changing means for changing the arrangement pattern of the pixels of the edge portion detected by the second edge detection means and the pixels around the pixel into a pixel arrangement pattern for smoothing the edge portion;
When the edge width detected by the edge width detecting means is narrower than a preset value, the pattern changing means is more than pixel data subjected to screen processing with a higher number of lines than the non-edge portion by the screen processing means. Selection means for preferentially selecting pixel data whose array pattern has been changed by:
An image processing apparatus.   When the edge width detected by the edge width detection means is wider than a preset value, the selection means is more non-deterministic by the screen processing means than pixel data whose array pattern has been changed by the pattern change means. The image processing apparatus according to claim 1, wherein pixel data subjected to screen processing with a higher number of lines than the edge portion is preferentially selected.   The edge width detecting means sequentially selects one of the pixels constituting the image data as a target pixel, and pixels having substantially the same pixel value as the target pixel are consecutive in the horizontal direction or the vertical direction from the target pixel. The image processing apparatus according to claim 1, wherein the number of pixels to be detected is detected as an edge width.   The image processing apparatus according to claim 1, wherein the gradation correction unit performs gradation correction so as to reduce a pixel value of a pixel at an edge portion when thinning processing is designated.   When the thinning process is designated, the pattern changing unit changes the arrangement pattern of the pixels in the edge portion and the pixels around the pixel to a pixel arrangement pattern for smoothing the edge portion and performing thinning. Item 5. The image processing apparatus according to any one of Items 1 to 4. A first operation for detecting whether or not the pixel of interest is a pixel constituting an edge portion is performed by performing a preset operation on the pixel values of pixels around the pixel of interest on the input image data. Edge detection means,
By detecting whether or not a pixel arrangement pattern around the pixel of interest matches a preset pixel arrangement pattern, it is detected whether or not the pixel of interest is a pixel constituting an edge portion. Edge detection means;
Edge width detection means for detecting an edge width, which is the width of the edge portion, of the pixels of the edge portion detected by the second edge detection means;
Gradation correction means for performing gradation correction for performing screen processing with a higher number of lines than the non-edge portion on the pixels of the edge portion detected by the first edge detection means;
Screen processing means for performing screen processing with a higher number of lines than the non-edge portion on the pixel data after the gradation correction is performed by the gradation correction means;
Pattern changing means for changing the arrangement pattern of the pixels of the edge portion detected by the second edge detection means and the pixels around the pixel into a pixel arrangement pattern for smoothing the edge portion;
When the edge width detected by the edge width detecting means is narrower than a preset value, the pattern changing means is more than pixel data subjected to screen processing with a higher number of lines than the non-edge portion by the screen processing means. Selection means for preferentially selecting pixel data whose array pattern has been changed by:
Image output means for outputting an image based on the pixel data selected by the selection means;
An image forming apparatus. A first operation for detecting whether or not the pixel of interest is a pixel constituting an edge portion is performed by performing a preset operation on the pixel values of pixels around the pixel of interest on the input image data. Edge detection step,
By detecting whether or not a pixel arrangement pattern around the pixel of interest matches a preset pixel arrangement pattern, it is detected whether or not the pixel of interest is a pixel constituting an edge portion. An edge detection step;
An edge width detecting step for detecting an edge width which is a width of the edge portion of the pixel of the edge portion detected in the second edge detecting step;
Performing gradation correction for performing screen processing with a higher number of lines than the non-edge portion on the edge portion pixels detected in the first edge detection step;
A step of performing screen processing with a higher number of lines than the non-edge portion on the pixel data after the gradation correction is performed;
Changing the arrangement pattern of the pixels of the edge portion detected in the second edge detection step and the pixels around the pixel to a pixel arrangement pattern for smoothing the edge portion; and
If the edge width detected in the edge width detection step is narrower than a preset value, the pixel whose array pattern has been changed from the pixel data subjected to screen processing with a higher number of lines than the non-edge portion A program for causing a computer to execute a step of preferentially selecting data.

Images