JP2006287595A - Image processor and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of moire without increasing the scale of an image processing circuit and to obtain high gradation reproducibility. <P>SOLUTION: A resolution setting part sets the resolution of error diffusion processing by an error diffusion processing part on the basis of an edge degree calculated by an edge degree calculating part and a density degree calculated by a density detecting part (S201 and S202), and the error diffusion processing part performs error diffusion processing of image data subjected to smoothing processing by a Gaussian filter part with the resolution set by the resolution setting part (S203 and S204). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing apparatus such as a scanner or a multifunction peripheral, and more particularly to an image processing apparatus and an image processing program for performing predetermined image processing on an input image and outputting the input image.

  Documents handled by image processing apparatuses such as scanners and printers are roughly divided into three types: character documents, halftone documents, and photographic documents. In order to reproduce these originals with high image quality in an image processing apparatus, it is necessary to suppress moire in halftone originals, improve character reproduction on halftone dots, and achieve both edge and gradation in photographic originals. In order to achieve this, various efforts have been made focusing on the area (image area) separation technology.

For example, in Patent Document 1, the output dots are concentrated by periodically changing the threshold according to the position of the pixel of interest on the original image in a specified density range including a high and medium density region within a predetermined range from the intermediate density. Thus, an image processing apparatus is disclosed in which high tone reproducibility is ensured while utilizing the original resolution of error diffusion processing.
JP 2001-169111 A

  However, according to the image processing apparatus disclosed in Patent Document 1, periodicity occurs in the concentrated output dots, so that the input image is a halftone print image, and the input image is processed by a smoothing filter. When the halftone dot cannot be completely removed, there is a problem that moire occurs in a specified density region due to interference with different periods.

  As a solution to the above problem, it is conceivable to increase the matrix size of the smoothing filter, but if the matrix size of the smoothing filter is increased, the edges of characters and photographs will be blurred, so that a very large matrix size cannot be used. . Therefore, a noticeable moire occurs in a halftone dot image having a relatively low number of lines. In order to solve this phenomenon, there is a method of accurately separating the halftone dot print image area and the character image area and applying a filter process adapted to each area. In this case, however, the required image processing circuit scale is small. There is a problem of growing.

  The present invention has been made in view of such a situation, and it is an object of the present invention to suppress the occurrence of moire without increasing the image processing circuit scale and to obtain high gradation reproducibility. is there.

The invention according to claim 1 is a smoothing filter means for performing a smoothing process on digitally input image data;
An edge degree calculating means for obtaining an edge degree of a pixel in the image data smoothed by the smoothing filter means;
A density detection means for obtaining a density value of a pixel in the image data subjected to the smoothing process by the smoothing filter means;
Error diffusion processing means for performing error diffusion processing as halftone processing on the image data subjected to smoothing processing by the smoothing filter means;
Resolution setting means for setting the resolution of the error diffusion processing by the error diffusion processing means based on the edge degree obtained by the edge degree calculation means and the density value detected by the density detection means;
The error diffusion processing means is an image processing apparatus that performs error diffusion processing on the image data after the smoothing processing by the smoothing filter means at the resolution set by the resolution setting means.

The invention according to claim 5 provides an information processing apparatus,
Smoothing filter means for performing a smoothing process on digitally input image data;
An edge degree calculating means for obtaining an edge degree of a pixel in the image data smoothed by the smoothing filter means;
A density detecting means for obtaining a density value of a pixel in the image data subjected to the smoothing process by the smoothing filter means;
Error diffusion processing means for performing error diffusion processing as halftone processing on the image data subjected to smoothing processing by the smoothing filter means;
A resolution setting means for setting the resolution of the error diffusion processing by the error diffusion processing means based on the edge degree obtained by the edge degree calculation means and the density value detected by the density detection means;
The error diffusion processing means is an image processing program that functions as an image processing apparatus that performs error diffusion processing on the image data smoothed by the smoothing filter means at the resolution set by the resolution setting means.

  According to these configurations, first, smoothing processing is performed on the digitally input image data by the smoothing filter means, so that halftone dots are effectively removed, regularity is lost, and generation of moire is suppressed.

  Next, for the pixels of the image data that have been smoothed by the smoothing filter means, the edge degree calculating means obtains the edge degree, and the density detecting means detects the density value. Subsequently, the resolution setting means determines the resolution of the error diffusion processing by the error diffusion processing means based on the edge degree of the pixel obtained by the edge degree calculation means and the density value of the pixel detected by the density detection means. Set. Then, the error diffusion processing means performs error diffusion processing on the image data that has been smoothed by the smoothing filter means, based on the error diffusion resolution set by the resolution setting means.

  As a result, the optimal resolution of the error diffusion processing is not based on the simple processing based on the edge degree and the density value of the pixels, but on the basis of the simple processing based on the edge degree and the density value of the pixels, instead of performing the image processing on each region obtained by performing the region separation on the entire image data. Therefore, it is possible to avoid an increase in the image processing circuit scale. Therefore, high gradation reproducibility can be obtained for any of characters, halftone originals, and photographic originals, and in particular, occurrence of moire during printing of photographic originals can be suppressed.

The invention according to claim 2 is the image processing apparatus according to claim 1, further comprising output means for outputting the image data after the error diffusion processing by the error calculation diffusion processing means at a preset resolution,
The resolution setting means, when the edge degree obtained by the edge degree calculating means is higher than a preset edge degree, the resolution of the error diffusion processing by the error diffusion processing means is the same as the output resolution of the output means The resolution is set.

  According to this configuration, when the edge degree obtained by the edge degree calculating means is higher than the preset edge degree, for example, when a character edge is assumed, the resolution setting means outputs the output from the output means. The error diffusion processing means is caused to perform error diffusion processing at the same resolution as the resolution. Thereby, the gradation of the character document can be reproduced well.

  A third aspect of the present invention is the image processing apparatus according to the first or second aspect, wherein the resolution setting means has an edge degree determined by the edge degree calculating means based on a preset edge degree. And the resolution value of the error diffusion processing by the error diffusion processing means is the same as the output resolution of the output means when the density value detected by the density detection means is outside a preset halftone density region The resolution is set.

  According to this configuration, the edge degree obtained by the edge degree calculating means is lower than the preset edge degree. For example, even when a pattern edge of a photographic document is assumed, the density detecting means If the detected density value is outside the preset halftone density area, the resolution setting means causes the error diffusion processing means to perform error diffusion processing at the same resolution as the output resolution of the output means. As a result, emphasizing the resolution, the edges of the picture parts of a photo document are clearly expressed, and the gradation of the picture parts of a photo document is reproduced well without causing graininess in the printed image. it can.

  A fourth aspect of the present invention is the image processing apparatus according to any one of the first to third aspects, wherein the resolution setting means is preset with the edge degree obtained by the edge degree calculating means. When the density value is lower than the edge degree and the density value detected by the density detection means is within the preset halftone density region, the resolution of the error diffusion processing by the error diffusion processing means is determined by the output means. A predetermined resolution lower than the output resolution is set.

  According to this configuration, the edge degree obtained by the edge degree calculating unit is lower than the predetermined edge degree, and for example, a pattern edge of a photographic document is assumed, and is detected by the density detecting unit. If the density value is within a preset halftone density region, the resolution setting means causes the error diffusion processing means to perform error diffusion processing at a resolution lower than the output resolution of the output means. In this case, in particular, in the reproduction of a halftone density area (halftone) of a photographic document, the dot arrangement at the time of image output is randomized by the error diffusion process, so that the generation of moire is suppressed and low resolution is achieved. By doing so, the interval between the dots is relatively widened, so that the contact between the dots is reduced and the gradation can be reproduced well.

  According to the first and fifth aspects of the present invention, high gradation reproducibility can be obtained for any of characters, halftone originals, and photographic originals without increasing the scale of the image processing circuit. Occurrence can be suppressed.

  According to the second aspect of the present invention, the gradation of a character original can be reproduced particularly well.

  According to the third aspect of the present invention, emphasis is placed on the resolution, and in particular, the edges in the highlight portion and the shadow portion of the picture portion of the photographic original are clearly expressed, and the printed image is grainy. Therefore, it is possible to satisfactorily reproduce the gradation of the pattern portion of the photographic original.

  According to the invention of claim 4, in particular, in the reproduction of a halftone density region of a photographic document, since the dot arrangement at the time of image output is randomized by the error diffusion process, the occurrence of moiré is suppressed, By using a low resolution, the distance between the dots is relatively widened, so that the contact between the dots is reduced and the gradation can be reproduced well.

  Hereinafter, as an example of an image processing apparatus according to the present invention, a multifunction machine having a printer function will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an internal configuration of a multifunction machine 1 which is an example of an image processing apparatus according to an embodiment of the present invention. The multifunction device 1 has functions such as a copy function, a printer function, a scanner function, and a facsimile function. The multi-function device 1 includes a main body 2, a stack tray 3 disposed on the left side of the main body 2, a document reading unit 5 disposed on the top of the main body 2, and an upper side of the document reading unit 5. And a document feeding unit 6 disposed.

  An operation unit 47 is provided at the front part of the multifunction machine 1. The operation unit 47 displays a start key 471 for a user to input a print execution instruction, a ten key 472 for inputting the number of copies to be printed, operation guide information for various copying operations, and the like. A display unit 473 formed of a liquid crystal display or the like having a touch panel function, a reset key 474 for resetting setting contents set in the display unit 473, and a stop key for stopping a printing (image forming) operation being executed 475 and a function switching key 477 for switching between a copy function, a printer function, a scanner function, and a facsimile function.

  The document reading unit 5 includes a scanner unit 51 including a CCD (Charge Coupled Device) sensor and an exposure lamp, and a document table 52 and a document reading slit 53 made of a transparent member such as glass. The scanner unit 51 is configured to be movable by a drive unit (not shown). When reading a document placed on the document table 52, the scanner unit 51 is moved along the document surface at a position facing the document table 52, and the document image is scanned. The image data acquired while scanning is output to the control unit 10 (FIG. 2). Further, when reading a document fed by the document feeding unit 6, the document is moved to a position facing the document reading slit 53 and synchronized with the document feeding operation by the document feeding unit 6 via the document reading slit 53. The image of the original is acquired and the image data is output to the control unit 10.

  The document feeding unit 6 includes a document placing unit 61 for placing a document, a document discharge unit 62 for discharging a document whose image has been read, and a document placed on the document placing unit 61. A document transport mechanism 63 including a paper feed roller (not shown), a transport roller (not shown) and the like for feeding the paper one by one to a position facing the document reading slit 53 and discharging it to the document discharge section 62 is provided. The document conveyance mechanism 63 further includes a sheet reversing mechanism (not shown) that reverses the document and reversely conveys the document to a position facing the document reading slit 53, and scans both sides of the document through the document reading slit 53. 51 can be read.

  The document feeding unit 6 is provided so as to be rotatable with respect to the main body unit 2 so that the front side thereof can move upward. By moving the front side of the document feeder 6 upward to open the upper surface of the document table 52, the operator can place a read document, for example, a book in a spread state, on the upper surface of the document table 52. It has become.

  The main body 2 includes a plurality of paper feed cassettes 461, a paper feed roller 462 that feeds the recording paper from the paper feed cassette 461 one by one and transports it to the recording unit 40, and a recording paper transported from the paper feed cassette 461. And a recording unit 40 for forming an image.

  The recording unit 40 is based on a charge eliminating device 421 that removes residual charges from the surface of the photosensitive drum 43, a charging device 422 that charges the surface of the photosensitive drum 43 after charge removal, and image data acquired by the scanner unit 51. The laser beam is output to expose the surface of the photosensitive drum 43, and an exposure device 423 for forming an electrostatic latent image on the surface of the photosensitive drum 43, and on the photosensitive drum 43 based on the electrostatic latent image. , Black (K), yellow (Y), magenta (M) and cyan (C) toner images of respective colors formed on the photosensitive drum 43 and developing devices 44K, 44Y, 44M, and 44C. The transfer drum 49 on which the image is transferred and superimposed, the transfer device 41 that transfers the toner image on the transfer drum 49 to the paper, and the paper on which the toner image has been transferred are heated to transfer the toner image to the paper And a fixing device 45 for fixing. Note that toner is supplied to each color of black, yellow, magenta, and cyan from a toner supply container (toner cartridge) (not shown). In addition, conveyance rollers 463 and 464 that convey the recording paper that has passed through the recording unit 40 to the stack tray 3 or the discharge tray 48 are provided.

  When forming images on both sides of the recording paper, the recording unit 40 forms an image on one side of the recording paper, and then the recording paper is nipped by the conveyance roller 463 on the discharge tray 48 side. In this state, the conveyance roller 463 is reversed to switch back the recording paper, and the recording paper is sent to the paper conveyance path L and conveyed again to the upstream area of the recording unit 40, and an image is formed on the other surface by the recording unit 40. Thereafter, the recording paper is discharged to the stack tray 3 or the discharge tray 48.

  FIG. 2 is a functional block diagram showing a schematic configuration of the multifunction machine 1 shown in FIG. The multifunction machine 1 includes a control unit 10 that controls the operation of the entire apparatus. The control unit 10 includes a document reading unit 5 including a scanner unit 51 and the like, a document feeding unit 6 including a document transport mechanism 63, and the like. Connected to the recording unit 40 including the developing device 44, the operation keys such as the start key 471 and the numeric keypad 472, the operation unit 47 including the display unit 473, the image memory 7, the HDD 8, the network I / F unit 9, and the image processing unit 11. Has been.

  The image memory 7 stores image data of a document (for example, a halftone document) read by the document reading unit 5 or image data transmitted from an external device (not shown) via a network I / F unit 9 described later. It is a memory that stores temporarily.

  An HDD (Hard Disk Drive) 8 is a storage device that stores image data of a document image read by the document reading unit 5, image data transmitted from an external device, an output format set in the image data, and the like. It is.

The network I / F unit 9 uses a network interface (for example, 10 / 100Base-TX) or the like to transmit and receive various data to and from an external device connected via a network such as a LAN.

  The image processing unit 11 performs various image processes on a document image (image data) obtained by reading a document by the document reading unit 5. In the image processing unit 11, for example, A / D conversion of image data is performed on a document image read by the document reading unit 5, and various image processing is performed using the A / D converted image data. The image processing unit 11 includes a Gaussian filter unit (an example of a smoothing filter unit) 111, an error diffusion processing unit (error diffusion processing unit) 112, and a γ (gamma) correction processing unit (γ correction processing unit) 113. .

  The Gaussian filter unit 111 performs Gaussian filter processing, which is smoothing processing for the purpose of image noise removal, on the image data. The Gaussian filter process is a process of taking a weighted average in which a large weight is given to a pixel near the target pixel and a small weight is given to a pixel far from the target pixel in consideration of the spatial arrangement of the pixels. Since a Gaussian function is used for this weighting, it is called a Gaussian filter. The weight can be easily controlled by the numbers in the Gaussian filter matrix.

  The error diffusion processing unit 112 is a functional unit that performs error diffusion processing on image data. This error diffusion process does not have a threshold table like the dither process, and diffuses the binarization error generated in the pixel of interest to the subsequent peripheral pixels so that the total ratio becomes 1, so that it is within a certain area. Binarization is performed with the average density maintained. The error diffusion processing unit 112 performs binarization processing on the target pixel using a predetermined threshold value, diffuses an error generated during the binarization processing to surrounding pixels before the binarization processing, and the error The binarization process is sequentially performed for each pixel in which is diffused as the target pixel. The binarization process is a process of converting a grayscale image into a binary (1 bit) image that includes only white and black and does not have a gray level of an intermediate color.

  The present invention has a feature in the resolution setting of the error diffusion process described above, and the resolution at the time of the error diffusion process is sequentially changed based on the edge degree and density of the target pixel to be subjected to the error diffusion process. Error diffusion processing is performed at the resolution. For example, when error diffusion processing is performed using two resolutions a and a resolution b that is half of the resolution a in accordance with the edge degree and density of the target pixel, the resolution a is 2 for all the pixels. When the binarization operation is performed and the respective binarization results are output, the resolution b performs the binarization operation every other pixel, and the target pixel of the binarization operation and the right, bottom, and right of the pixel. The same binarization result is output for the lower four pixels.

The γ correction processing unit 113 is a functional unit that performs γ correction processing on image data. The γ correction process is a process for adjusting brightness, and is performed by converting the pixel value of each pixel with an exponential function. In an image sensor such as a CCD, is provided between the output value D to the input light intensity E, relationship usually referred D = E ^gamma. Adjusting the value of γ is γ correction. Further, the input-to-output conversion for correcting with the optimum γ value is tabulated as a γ correction table.

  The control unit 10 includes a ROM (Read Only Memory) that stores a control program of the multifunction device 1, a RAM (Random Access Memory) that temporarily stores data, and a micro information processing that reads and executes a control program from the ROM. The apparatus includes a device and the like, and executes processing for controlling the entire device in accordance with instruction information input in the operation unit 47 and detection signals from various sensors provided in various places of the device. The control unit 10 includes an edge degree calculation unit (edge degree calculation unit) 101, a density detection unit (density detection unit) 102, a resolution setting unit (resolution setting unit) 103, and a predetermined value storage unit 105.

  The edge degree calculation unit 101 calculates the edge degree of the target pixel based on the image data that has been smoothed by the Gaussian filter unit 111. The density detection unit 102 detects the density value of the target pixel from the image data that has been smoothed by the Gaussian filter unit 111.

  The resolution setting unit 103 determines the resolution at the time of the error diffusion processing by the error diffusion processing unit 112 based on the edge degree obtained by the edge degree calculation unit 101 and the density value obtained by the density detection unit 102, Set an appropriate resolution.

  The predetermined value storage unit 105 stores in advance threshold values that are referred to when the resolution setting unit 103 determines the resolution at the time of error diffusion processing by the error diffusion processing unit 112, that is, a predetermined edge degree and a predetermined density value. is there.

  FIG. 3 is a diagram schematically showing a flow of image processing in the image processing apparatus according to the embodiment of the present invention. First, for example, a document is read using the scanner function of the multifunction machine 1 to create image data (S101). Subsequently, the γ correction processing unit 113 performs input (scanner) γ correction processing on the image data (S102). Here, the input γ correction processing is a density conversion curve indicating the relationship between the output density and the input density of the image data, that is, a method of correcting the shading of the image by changing the input / output relationship using the γ curve. Image processing for adjusting brightness, color saturation, and the like.

  Then, the Gaussian filter unit 111 performs a smoothing process using a Gaussian filter on the image data on which the input γ correction process has been performed (S103). By this process, the halftone dot component is appropriately removed, so that, for example, even a halftone original exhibits gradation characteristics equivalent to those of a photographic original. This smoothing process is performed for the purpose of removing noise, reducing the amount of image data, etc., in addition to obtaining the above-mentioned gradation characteristics.

For example, the pixel value XX after the target pixel is smoothed is obtained as follows. FIGS. 4A and 4B are 7 × 7 matrices showing an embodiment of a Gaussian filter. FIG. 4A is a diagram showing the count of each pixel, and FIG. 4B is a symbol showing pixels at each position. FIG. The pixel value XX after the smoothing process of the target pixel is obtained as follows using the pixel value of the pixel indicated by diagonal lines in FIG. 4B and the coefficient of each pixel shown in FIG. .
XX = (a3 * 1 + a4 * 1 + a5 * 1 + b2 * 1 + b3 * 2 + b4 * 3 + b5 * 2 + b6 * 1 + c1 * 1 + c2 * 2 + c3 * 4 + c4 * 5 + c5 * 4 + c6 * 2 + c7 * 1 + d1 * 1 + d2 * 3 + d3 * 5 + d4 * 7 + d5 * 5 + d6 * 3 + d7 * 1 + e1 * 1 + e2 * 2 + e3 * 4 + e4 * 5 + e5 * 4 + e6 * 2 + e7 * 1 + f2 * 1 + f3 * 2 + f4 * 3 + f5 * 2 + f6 * 1 + g3 * 1 + g4 * 1 + g5 * 1 ) / 87

  Returning to FIG. 3, the edge degree of the image data after the Gaussian filter processing is first calculated by the edge degree calculation unit 101 for each target pixel, and the density value of the target pixel is detected by the density detection unit 102 (S104). ).

Further, the calculation of the edge degree S of the target pixel XX will be described with reference to FIG. 4B. Based on the pixel value of each pixel of the image data after the Gaussian filter processing,
S = XX + 0.5 {4 * XX- (A + B + C + D)}
It is calculated by the following formula. The embodiment of the edge degree calculation according to the present invention is not limited to this, and may include any form calculated from the pixel value of the target pixel and the pixel values of the surrounding pixels. Further, the density value of the target pixel is detected by the density detection unit 102.

  Subsequently, the resolution setting unit 103 sets the resolution of the error diffusion processing of the error diffusion processing unit 112 based on the edge degree calculated by the edge degree calculation unit 101 and the density value calculated by the density detection unit 102. (S104). Details of the resolution setting of this error diffusion processing will be described later.

  Subsequently, if requested, the image data is enlarged or reduced (S105). As a method for performing the enlargement process, for example, there are interpolation methods such as nearest neighbor method, linear interpolation or cubic convolution. Further, output (printer) γ correction is subsequently performed on the image data on which the enlargement or reduction processing has been performed (S106).

  Further, error diffusion processing is performed on the image data on which the output γ correction has been performed (S107). At this time, the error diffusion processing unit 112 performs error diffusion processing at the resolution set by the resolution setting unit 103. The image data after the error diffusion processing is printed and output by the recording unit 40 (S108).

  The flow of resolution setting by the resolution setting unit 103 and error diffusion processing by the error diffusion processing unit 112 will be described. FIG. 5 is a flowchart showing the flow of resolution setting by the resolution setting unit 103 and error diffusion processing by the error diffusion processing unit 112. In this embodiment, an 8-bit scale (0 to 255) is used, an edge degree threshold TH_edge (predetermined edge degree) is set to 128, a density value threshold (predetermined density value) is set to 64, and TH_dens1 is set to 64. An example in which TH_dens2 is set to 192 will be described. These threshold values are stored in the predetermined value storage unit 105, for example.

  First, the resolution setting unit 103 compares the edge degree calculated by the edge degree calculating unit 101 with TH_edge (S201). As a result, when the edge degree is equal to or higher than TH_edge (YES in S201), there is a high possibility that this target pixel is a character edge or the like, so the resolution setting unit 103 sets the resolution of the error diffusion processing by the error diffusion processing unit 112. The output resolution of the recording unit (an example of output means) 40 (for example, the maximum output resolution by the recording unit 40. When the maximum output resolution by the recording unit 40 is 600 dpi, the maximum output resolution by the recording unit 40 is 1200 dpi. If it is, the error diffusion processing unit 112 performs error diffusion processing at the set resolution (S204). As a result, the gradation is expressed by dots having a small size and a relatively large number, so that the character edge or the like can be sharply displayed and the gradation of the character portion can be reproduced well.

  If the edge degree calculated by the edge degree calculating unit 101 is less than TH_edge (NO in S201), the resolution setting unit 103 continues to have a density value detected by the density detecting unit 102 greater than TH_dens1 and greater than TH_dens2. It is also determined whether it is in the halftone density region, which is within a small range (S202). As a result, when the density value detected by the density detection unit 102 is equal to or lower than TH_dens1 or higher than TH_dens2 (YES in S202), the resolution setting unit 103 determines the resolution of the error diffusion processing by the error diffusion processing unit 112. Are set to the same resolution (same as above) as the resolution of the recording unit 40, and the error diffusion processing unit 112 performs error diffusion processing at the set resolution (S204). In this case, it is assumed that the pixel is a highlight portion or a shadow portion in the pattern portion of the photographic document, but since error diffusion processing is performed with emphasis on resolution, graininess is generated in the printed image. In addition, the gradation can be reproduced well, and the edges in the pattern portion of the photo original can be clearly expressed.

  In contrast to the above, when the density value detected by the density detection unit 102 is larger than TH_dens1 and smaller than TH_dens2 (NO in S202), that is, when the target pixel is in the halftone density region, this attention is made. Although the pixel is assumed to be an image part edge or the like, the resolution setting unit 103 sets the resolution of the error diffusion processing by the error diffusion processing unit 112 to a predetermined resolution lower than the resolution of the recording unit 40. The error diffusion processing unit 112 performs error diffusion processing at the set resolution (S203). The resolution used as the “predetermined resolution lower than the resolution of the recording unit 40” is not particularly limited. In the present embodiment, the resolution is half the maximum output resolution of the recording unit 40. The resolution. For example, when the maximum resolution by the recording unit 40 is 600 dpi, it is 300 dpi, and when the maximum resolution by the recording unit 40 is 1200 dpi, it is 600 dpi. When the error diffusion process is performed as in S203, the error diffusion process is performed at a relatively low resolution. Therefore, in the reproduction of the halftone density region (intermediate gradation) in the pattern portion of the photographic document, the dot arrangement is random. Therefore, the generation of moire is suppressed. In addition, since the distance between the dots is relatively widened by the error diffusion processing at a low resolution, the contact between the dots is reduced, and the gradation can be reproduced well.

  When it is assumed that a pixel that causes inconvenience in binarization conversion occurs when the resolution is switched, the binarization conversion process is performed on the pixel at the same resolution as the resolution of the recording unit 40. Thus, the inconvenience may be solved.

  As described above, according to the embodiment of the present invention, since smoothing processing is performed on digitally input image data using a Gaussian filter of a predetermined matrix size, for example, halftone dots are effectively used. It is possible to eliminate the occurrence of moiré and to provide appropriate gradation characteristics.

  In addition, instead of performing separate image processing for each region that has been subjected to region separation for the entire image data, the optimal error diffusion processing is based on simple processing based on the edge degree and density value of the pixel. Since the resolution is set, it is possible to avoid an increase in the size of the image processing circuit.

  FIG. 6 illustrates an error diffusion pattern by the multifunction machine 1 according to an embodiment of the present invention. 6A is a diagram showing an error diffusion pattern when error diffusion processing is performed at a constant resolution, and FIG. 6B is a diagram showing a pattern when image processing is performed using the conventional technique shown in Patent Document 1. (C) is a figure which shows an error diffusion pattern at the time of performing an error diffusion process with the multifunctional device 1 which is one Embodiment of this invention.

  As shown in FIG. 6A, when error diffusion processing is performed at a constant resolution, dots are randomly arranged and moiré is suppressed, but the dot density is changed (the number of dots is changed). Since the gradation is expressed), the dots are in contact with each other in the halftone density region, and the gradation cannot be reproduced satisfactorily. In this case, the tone can be reproduced well without any problem with respect to the character edge and the like, but in the halftone density region in the pattern portion of the photographic document, it means that the tone cannot be reproduced well due to the contact of the dots.

  As shown in FIG. 6B, when the image processing is performed by the conventional technique shown in Patent Document 1, in the halftone density region, the intervals between the dots are separated, and the gradation is determined by the size of the dots. Although it is expressed, the dots are periodically arranged, which causes the generation of moire.

  On the other hand, according to the error diffusion process by the multifunction machine 1 according to the embodiment of the present invention, as shown in FIG. 6C, in the intermediate density region, the error diffusion process is performed to randomly set dots. Since the dots are separated and the dots are spaced apart to represent the gradation by the size of the dots, the gradation reproducibility is reduced due to contact between the dots, and the dots are periodically arranged. Gradation can be reproduced well without causing the problem of moiré due to.

[Other preferred embodiments]
The present invention is not limited to the configuration of the above embodiment, and various modifications can be made.

  (A) In the above embodiment, it has been described that the predetermined edge degree and the predetermined density value used for determining the resolution of the error diffusion processing are set in advance and stored in the predetermined value storage unit 105. However, the embodiment of the present invention is not limited thereto, and the predetermined edge degree and the predetermined density value may be configured to be settable by the user by operating the operation unit 47 or the like, for example.

  As a result, the user of the image processing apparatus himself / herself changes the set value of the predetermined edge degree, for example, a boundary that separates a part having a high edge degree such as a character or an edge of a picture part and a part having a low edge degree such as a picture part. Can be moved. Furthermore, by changing the set value of the predetermined density value, for example, a boundary that separates a portion having a higher edge degree such as a character edge and a portion having a lower edge degree than a character edge such as a pattern edge is moved. Can do. Thus, it is possible to perform image processing in accordance with the type of image data, the user's intention, and the like.

  (B) In the embodiment described above, a Gaussian filter having a matrix size of 7 × 7 is shown in FIG. 4, but the embodiment of the present invention is not limited to this, and the size of these filters, the numbers in the block, and those The position of the numbers can be changed freely.

  For example, the matrix size of the Gaussian filter may be increased to perform smoothing over a wider range, and conversely, the matrix size may be decreased to reduce the range of smoothing. Even if the matrix size is the same, if you want to increase the degree of smoothing, you can increase the variance associated with the Gaussian filter. Conversely, if you want to reduce the degree of smoothing so that the original image data remains, reduce the variance. do it.

  (C) Note that the edge degree calculation unit 101, the density detection unit 102, and the resolution setting unit 103 of the control unit 10, the Gaussian filter unit 111 of the image processing unit 11, the error diffusion processing unit 112, and The γ correction processing unit 113 or the like may be configured such that each of these units individually includes a circuit or the like, or one control circuit functions as each of the above units according to an image processing program stored in the HDD 8 or the like. Good.

1 is a cross-sectional view schematically illustrating an internal configuration of a multifunction machine that is an example of an image processing apparatus according to an embodiment of the present invention. FIG. 2 is a functional block diagram illustrating a schematic configuration of the multifunction peripheral illustrated in FIG. 1. It is a figure which shows roughly the flow of the image processing in the image processing apparatus which concerns on one Embodiment of this invention. (A) (b) is a 7 × 7 matrix showing one embodiment of a Gaussian filter, (a) is a diagram showing the count of each pixel, and (b) is a symbol showing the pixel at each position. FIG. It is a flowchart which shows the flow of the resolution setting by a resolution setting part, and the error diffusion process by an error diffusion process part. (A) is a diagram showing an error diffusion pattern when error diffusion processing is performed at a constant resolution, (b) is a diagram showing a pattern when image processing is performed by the conventional technique shown in Patent Document 1, FIG. 6C is a diagram illustrating an error diffusion pattern when error diffusion processing is performed by the multifunction peripheral according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multifunction device 10 Control part 101 Edge degree calculation part 102 Density detection part 103 Resolution setting part 11 Image processing part 111 Gaussian filter part 112 Error diffusion process part 40 Recording part

Claims (5)

Smoothing filter means for performing a smoothing process on digitally input image data;
An edge degree calculating means for obtaining an edge degree of a pixel in the image data smoothed by the smoothing filter means;
A density detecting means for obtaining a density value of a pixel in the image data subjected to the smoothing process by the smoothing filter means;
Error diffusion processing means for performing error diffusion processing as halftone processing on the image data subjected to smoothing processing by the smoothing filter means;
A resolution setting means for setting the resolution of the error diffusion processing by the error diffusion processing means based on the edge degree obtained by the edge degree calculation means and the density value detected by the density detection means;
The error diffusion processing means is an image processing apparatus for performing error diffusion processing on image data after smoothing processing by the smoothing filter means at the resolution set by the resolution setting means. Further comprising output means for outputting the image data after error diffusion processing by the erroneous calculation diffusion processing means at a preset resolution;
The resolution setting means, when the edge degree obtained by the edge degree calculating means is higher than a preset edge degree, the resolution of the error diffusion processing by the error diffusion processing means is the same as the output resolution of the output means The image processing apparatus according to claim 1, wherein the resolution is set to a resolution.   The resolution setting means has an edge degree obtained by the edge degree calculating means lower than a preset edge degree, and the density value detected by the density detecting means is outside the halftone density region where the preset is set. 3. The image processing apparatus according to claim 1, wherein the resolution of the error diffusion processing by the error diffusion processing unit is set to the same resolution as the output resolution of the output unit.   The resolution setting means has a halftone density region in which the edge degree obtained by the edge degree calculation means is lower than a preset edge degree and the density value detected by the density detection means is the preset halftone density region. 4. The image processing according to claim 1, wherein the resolution of the error diffusion processing by the error diffusion processing unit is set to a predetermined resolution lower than the output resolution of the output unit. apparatus. Information processing device
Smoothing filter means for performing a smoothing process on digitally input image data;
An edge degree calculating means for obtaining an edge degree of a pixel in the image data smoothed by the smoothing filter means;
A density detecting means for obtaining a density value of a pixel in the image data subjected to the smoothing process by the smoothing filter means;
Error diffusion processing means for performing error diffusion processing as halftone processing on the image data subjected to smoothing processing by the smoothing filter means;
A resolution setting means for setting the resolution of the error diffusion processing by the error diffusion processing means based on the edge degree obtained by the edge degree calculation means and the density value detected by the density detection means;
The error diffusion processing means is an image processing program that functions as an image processing apparatus that performs error diffusion processing on image data that has been smoothed by the smoothing filter means at the resolution set by the resolution setting means.

Images