JP2007081657A - Image processor, image recording device, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor capable of solving the problem of occurrence of isolated dots due to error diffusion and the problem of defects due to the light amount difference in a multibeam system, and to provide an LED array system, an image recording device, and a program. <P>SOLUTION: When multiple-value (M-value) image data are recorded by using a dot, corresponding to each of N-values, while quantizing the multiple-value (M-value) image data into N-values (M>N≥2), by using an error diffusion method or an average error minimization method, the diffusion coefficients in the neighborhood pixels of a target pixel is set to ≤0 for the error diffusion matrix. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image recording apparatus, and a program for printing multivalued image data with high definition and high gradation.

  As an exposure method of the electrophotographic process, an LED array type image recording apparatus (image forming apparatus) in which a plurality of light emitting diodes (LEDs) are linearly arranged and mounted on one surface of an electrically insulating substrate as a light source of a printer is known. It has been. Since this exposure method uses an LED array as a light source, the entire apparatus can be made compact as compared with electrophotography having a writing optical system using a semiconductor laser. In addition, since each LED array performs writing in parallel, high-speed output can be achieved relatively easily. An optical printer using such an LED array element is generally superior to a deformation of an optical system due to vibration or heat as compared with a laser raster optical printer.

  However, in an LED head, for example, color unevenness may occur in an image formed due to variations in performance between LED chips, a decrease in spot light quantity between adjacent LED chips, and variations in LED elements. To solve this problem, an LED array that corrects unevenness in light quantity by installing an element that diffuses light after the light source, blurring the focus only at the peak part of the light quantity, and aligning the level at the low light quantity part, Has been proposed that performs light amount correction by oscillating the light in the direction in which the LED elements are arranged with a piezoelectric element (piezo element) or the like and averaging the light amount. Here, as is well known, a piezo element is an element that transforms electro-mechanical energy at an extremely high speed because the crystal structure is distorted by application of a voltage.

  In addition, as an exposure method for other electrophotographic processes, a multi-beam image recording apparatus (image forming apparatus) that performs image recording by collectively scanning a plurality of light beams on a photosensitive body in order to perform image recording at high speed. )It has been known. For example, in Patent Document 1, in a recording apparatus that scans a recording medium with a plurality of beams and records information on the recording medium, a beam detector is provided outside an effective scanning area of the plurality of beams, and the plurality of beams The selected beam is controlled to pass through the beam detector in a lit state, and a plurality of electrical modulation signals for modulating a plurality of beams are generated based on the output of the beam detector, A beam recording apparatus is disclosed in which the recording start positions of a plurality of beams on a recording medium are made to coincide with each other by delay-controlling modulation signals corresponding to the respective arrangements of beams.

  However, in the multi-beam method, as in the LED array method, color unevenness may occur in an image due to variation in performance of each LD or a decrease in spot light quantity between adjacent LDs. Here, for example, Patent Document 2 discloses a recording apparatus that corrects a light amount variation by shifting the phase of a clock for turning on an LD for each LD.

  Moreover, it is difficult to completely eliminate the light quantity difference between all the LDs and LEDs in both the multi-beam method and the LED array method. Complete adjustment in the production zone increases the production cost, and producing only with an LD having no light amount difference causes a slight difference in the light amount due to an increase in the procurement cost of the LD.

  There is a color difference problem of a repeat image as an example of a defect due to a slight light amount difference in a multi-beam printer. Here, a case will be described as an example where the number of LDs in the multi-beam method is two and images with dots biased in odd or even rows are output continuously by the same printer. There is no problem if the LD for writing odd rows and the LD for writing even rows are the same in the first output and the second and subsequent writes. However, if an LD is written as an odd-numbered row in the first writing, and a second even-numbered row is written, a density difference occurs in the obtained image. This phenomenon appears remarkably as a color difference when toners of two colors and three colors are overlapped. In order to suppress this phenomenon, (1) the dots are not biased to either the odd or even rows, or (2) the LD for writing the odd rows is always the same so that no problem occurs. Since the incorporation of such an LD control mechanism results in an increase in cost, there has been a demand for a process that prevents dots from being biased to either odd or even rows.

  In addition, as an example of a problem due to a slight light amount difference in an LED array type printer, there is a problem that a color difference occurs in the background color between pages in the background color of a printed material that covers a plurality of pages. This problem occurs when the background color of a certain page is biased to the odd-numbered columns and the background color of another page is biased to the even-numbered columns. There has been a need for a process that prevents dots from being biased to either odd or even rows on any page.

  By the way, there is an image input / output system that outputs multi-value image data read by an input device such as a scanner or a digital camera to an output device such as a printer or a display. At that time, multi-valued image data read by the input device (for example, 256 gradations for 8-bit accuracy) is converted into image data of the number of gradations that can be output by the output device, and pseudo continuous gradation is expressed. As a method for doing this, there is a halftone process.

  In particular, binarization processing is conventionally performed when the output device can express only binary values of ON / OFF of dots. Among these binarization processes, there are an error diffusion method and an average error minimum method that are excellent in both resolution and gradation. The error diffusion method and the minimum average error method are logically equivalent, only differing when the error diffusion operation is performed. Hereinafter, the error diffusion will be described.

  There is a process in which quantization by the error diffusion method is applied not only to binary but also to the number of gradations of 3 or more. Similar to binarization, processing with excellent gradation and resolution is possible.

  By the way, in the electrophotographic process, since the spatial frequency response deteriorates in each process of exposure, development, transfer, and fixing including MTF (Modulation Transfer Function) of the photoreceptor, an image structure in which isolated dots exist. However, there is a problem that even if the signal is input as a recording signal, the reproducibility varies and sufficient gradation reproduction cannot be performed.

  In particular, the error diffusion method is a halftone process in which dots are dispersed according to density by diffusing a quantization error to surrounding pixels when the dots are output, and many isolated dots are generated in the highlight portion. Therefore, when error diffusion is used as halftone processing in an electrophotographic process, it is necessary to cope with the problem of variation in reproducibility of isolated dots.

  In order to solve the above problem, Patent Document 3 superimposes a dot-concentrated dither on the threshold value, so that each dot quantized by error diffusion gathers like a dot-concentrated dither superimposed on the threshold value. A forming technique is disclosed. However, since the number of dither gradations is too small with respect to the input value in the technique of Patent Document 3, there are many gradations that do not follow the dither pattern, and these gradations have a disadvantage that graininess is not preferable.

  Further, Patent Document 4 discloses a technique for forming a cluster by increasing the value of an error diffusion matrix coefficient as the position is farther from a target pixel for quantizing. However, in the technique of Patent Document 4, the error diffusion matrix has to be increased in order to facilitate the formation of clusters, which increases the memory for storing errors and increases costs. Further, the total value of the error diffusion matrix is 1, and there is a limit to the difference between the coefficient at the position close to the target pixel and the coefficient at the position far from the target pixel as disclosed in Patent Document 4.

Patent Document 5 discloses a technique for storing a previously quantized state and forming a cluster by changing a threshold according to the quantum state in the vicinity of the target pixel. However, the technique of Patent Document 5 requires a memory for storing the already quantized state, resulting in an increase in cost.
JP-A-56-104572 JP 2004-262234 A JP 2001-177722 A JP 2002-218239 A Japanese Patent Application No. 2004-2775

  By the way, if the error diffusion is simple in the halftone process of the image recording apparatus adopting the LED array method as the exposure method of the electrophotographic process, no major problem occurs. Even if there is a slight amount of light difference between each LD in the multi-beam method or between each LED in the LED array method, error diffusion is a halftone process in which dots are dispersed according to the density, so a plurality of LDs -It is for using LED equally.

  However, when error diffusion is used for halftone processing in an image recording apparatus of an electrophotographic process that employs an LED array method even in a multi-beam method having a slight light amount difference, a plurality of LD / LEDs are evenly formed while forming a cluster. The technology to use has become necessary.

  Although this is an error diffusion method with excellent resolution and gradation, it is difficult to suppress the generation of isolated dots and to realize abnormal image suppression at a low cost by the multi-beam method using the LED array method.

  The present invention has been made in view of the circumstances described above, and an object of the present invention is to provide an image processing apparatus and an image recording apparatus that can solve the problem of isolated dots due to error diffusion and the problem of the multi-beam method using the LED array method. It is to provide an apparatus and a program.

  In order to solve the above problems, in the image processing apparatus, the image recording apparatus, and the program according to the present invention, in the error diffusion method or the average error minimum method, a plurality of dots are collected to form a cluster, and a plurality of LDs / LEDs are evenly distributed. By using this, an output result with good image quality can be obtained.

  In order to achieve such an object, the invention according to claim 1 quantizes multi-value (M-value) image data into N values (M> N ≧ 2) using an error diffusion method or an average error minimum method, An image processing apparatus that performs printing using dots corresponding to each of the N values, and the error diffusion matrix is characterized in that a diffusion coefficient of a pixel in the vicinity of the target pixel is 0 or less.

  The invention according to claim 2 is characterized in that the error diffusion matrix is more negative as the diffusion coefficient of the pixel closer to the target pixel.

  According to a third aspect of the present invention, the error diffusion matrix is characterized in that the diffusion coefficient of adjacent pixels in the main scanning direction is negatively larger than the diffusion coefficient of adjacent pixels in the sub-scanning direction.

  According to a fourth aspect of the present invention, the error diffusion matrix is characterized in that the diffusion coefficient of adjacent pixels in the sub-scanning direction is negatively larger than the diffusion coefficient of adjacent pixels in the main scanning direction.

  The invention described in claim 5 is characterized in that dots are easily connected in the main scanning direction in LED array type electrophotography.

  The invention described in claim 6 is characterized in that dots are easily connected in the sub-scanning direction in multi-beam electrophotography.

  The invention according to claim 7 is characterized in that the error diffusion matrix has a sum of all coefficients of one.

  According to the present invention, it is possible to provide an image processing apparatus, an image recording apparatus, and a program that can solve the problem of an isolated dot due to error diffusion and the problem of the LED array system in the multi-beam system.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. Components are distinguished by adding symbols. FIG. 1 is a diagram showing a block configuration of an image processing apparatus according to the present embodiment (particularly, a block configuration of an image processing unit that performs image processing characteristic of the present invention). FIG. 2 is a diagram showing the configuration of the image recording apparatus according to the present embodiment.

  Referring to FIG. 1, the image processing apparatus (image processing unit) 102 converts 256 gradation image data input from the image input apparatus 101 into the number of gradations that can be output by the subsequent image output apparatus 103. Perform the process. In this gradation number conversion process, the average error minimum method may be used. The image data quantized by the image processing apparatus 102 is sent to an image recording apparatus (image forming apparatus, image output apparatus) 103 as shown in FIG. Description will be made assuming that the number of gradations that can be output by the image output apparatus 103 is binary.

  In FIG. 2, the paper on which an image is to be formed is set on the main body tray 201 or the manual feed tray 202, and the conveyance of the paper is started by the paper feed roller 203 from the tray 201 or 202. Prior to the conveyance of the sheet by the sheet feeding roller 203, the photosensitive member (photosensitive drum) 204 rotates, the surface of the photosensitive member 204 is cleaned by the cleaning blade 205, and then uniformly charged by the charging roller 206. The Here, the laser beam modulated in accordance with the image signal is exposed from the laser optical system unit 207, developed by the developing roller 208, and the toner adheres. Made.

  The sheet fed from the sheet feeding roller 203 is conveyed while being sandwiched between the photosensitive drum 204 and the transfer roller 209, and at the same time, a toner image is transferred to the sheet. The transferred toner remaining on the photosensitive member 204 is scraped off again by the cleaning blade 205.

  A toner density sensor 210 is provided in front of the cleaning blade 205, and the density of the toner image formed on the photoconductor 204 can be measured by the toner density sensor 210. The sheet on which the toner image is placed is conveyed to the fixing unit 211 along the conveyance path, and the toner image is fixed on the sheet in the fixing unit 211.

  The printed sheets finally pass through the paper discharge roller 212 and are discharged in page order with the recording surface down. By the way, the laser optical system unit 207 is connected to a video control unit 271 and an LD drive circuit 272. The video control unit 271 controls an image signal from a personal computer or a workstation or holds it inside. The generated evaluation chart (test pattern) signal or the like is generated.

  Further, the developing roller 208 is applied with a high voltage bias by a bias circuit 214. By controlling the bias in the bias circuit 214, it is possible to control the overall density of the image. Yes.

  FIG. 3 is a perspective view showing an example of a positional relationship with a photosensitive drum as a latent image carrier on which a light beam emitted from the laser optical system unit 207 of FIG. 2 is written.

  In FIG. 3, 11 and 12 are laser diodes (semiconductor lasers), 13 and 14 are collimating lenses, 15 is an optical member for optical path synthesis, 16 is a quarter wavelength plate, and 17 and 18 are beam shaping optical systems. Each of these optical elements 11 to 18 constitutes a laser light source section (beam light source) Sou. The two light beams P1 emitted from the laser light source unit Sou are converted into parallel light beams by the collimator lenses P1 and P2, and are guided to the polygon mirror 19 constituting a part of the scanning optical system. Reflected and deflected in the main scanning direction Q1 by the surfaces 20a to 20f.

  The reflected and deflected light beam is guided to reflecting mirrors 21 and 22 constituting a part of the fθ optical system, and the reflected and deflected light beam passes through the fθ optical system 23 and is obliquely reflected. 24 and is guided to the surface 26 of the photosensitive drum 25 as a latent image carrier by the oblique reflection mirror 24. The surface 26 of the photosensitive drum 25 is linearly scanned in the main scanning direction Q1 by the light beam P1. This surface 26 is a surface to be scanned by the light beam P1, and writing is performed on this surface to be scanned.

  The laser optical system unit 207 is provided with synchronization sensors 27 and 28 on both sides in the longitudinal direction of the reflection mirror 24 (main scanning direction Q1 of the light beam). The synchronization sensor 27 is used for determining the write start timing, and the sync sensor 28 is used for determining the write end timing.

  Here, the laser optical system unit 207 of FIG. 2 may be an LED array optical system unit. As shown in FIG. 4, the LED array optical system unit 207 is a light emitting diode (LED) D, which is a large number of minute light emitters (which is illustrated in a simplified manner in FIG. Are arranged in a straight line, and an optical system composed of a plurality of equal-magnification imaging optical systems 402 arranged to face the LED array 401 at a fixed distance. The light emitted from the light-emitting diodes D of the LED array 401 is condensed by each equal-magnification imaging optical system 402 to form an imaging pattern on the photosensitive member 204. For example, a self-focal lens array (SLA) manufactured by Nippon Sheet Glass Co., Ltd. is used as the 1 × magnification optical system 402.

  As shown in FIG. 5, the light emitting diodes D on the LED array 401 are arranged in N columns in a straight line in the main scanning direction. For example, in this example, four M rows are arranged in a straight line in the sub-scanning direction. Has been. The intervals between the adjacent light emitting diodes D in the main scanning direction are all equal to L, and the intervals between the adjacent light emitting diodes D in the sub scanning direction are all equal to L. Further, the arrays in the main scanning direction and the sub-scanning direction are orthogonal to each other with θ = 90 °.

  A plurality of light emitting diodes D arranged in a straight line in the main scanning direction and the sub-scanning direction are respectively arranged on an electrically insulating substrate 403 fixed integrally on a base plate 404 as shown in FIG. Thus, the LED array 401 is configured. The LED array optical system unit 207 associates a light emitting diode D with a base pot 404 that integrally fixes the LED array 401, and a single-magnification imaging optical system 402 that is a rod-like self-focusing lens on each frame body 601. As shown in FIG. 7, it is configured by a lens array in which a plurality of rows (four rows) are arranged in a straight line, and a housing 602 shown in FIG. 6 made of polycarbonate resin (see also FIG. 7). .

  The base pot 404 is fixed to the bottom of the housing 602 with an adhesive, for example, and the lens array is also fixed to the top of the housing 602 with an adhesive, and in the fixed state, the center of each light emitting diode D (matches the optical axis). ) Are positioned on the optical axis of the bar-shaped equal-magnification imaging optical system 402, respectively. The LED array optical system unit 207 selectively selects each of the light emitting diodes D arranged in a straight line in the main scanning direction and the sub-scanning direction by an external electric signal corresponding to the image to be formed. The light emitted from each light emitting diode D is imaged on the surface of the photosensitive member 204 through the lens array, and is exposed on the photosensitive member 204.

  Further, the image recording apparatus 103 can apply the processing method according to the present invention even when an image is recorded (image formation) using an inkjet method.

  In the system configuration diagram of FIG. 1, each device is illustrated as independent depending on the processing. However, the present invention is not limited to this, and the form in which the function of the image processing device 102 exists in the image input device 101 or the image Some forms exist in the output device 103.

  FIG. 8 is a block diagram showing the configuration of the image processing apparatus 102 of the present embodiment shown in FIG.

  The input terminal 801 receives multivalued image data from the image input device 801. Here, in order to represent two-dimensional image data, it is represented as In (x, y) (x represents an address in the main scanning direction of the image, and y represents an address in the sub scanning direction).

  Next, the input data In (x, y) is input to the adder 802. The adder 802 adds the input data In (x, y) and the error component E (x, y) to obtain correction data C (x, y), and subtracts the correction data C (x, y) from the comparison determination unit 803. To the device 805.

  The comparison determination unit 803 outputs the density value Out () as follows based on the correction data C (x, y) obtained by adding the error E (x, y) to the input data In (x, y) and the threshold Th. x, y) is determined. The threshold value Th is set to an intermediate value 127 between the output values 0 and 255 in the case of binary error diffusion.

If (C (x, y) <Th)
then Out (x, y) = 0 (1)
Else
then Out (x, y) = 255 (2)

  This Out (x, y) is output from the output terminal 804 to the image output device 103.

  Further, the output value Out (x, y) is input to the subtracter 805. The subtracter 805 subtracts the correction data C (x, y) and the output value Out (x, y) as shown in the equation (5), and calculates an error e (x, y) generated in the current pixel.

    e (x, y) = C (x, y) −Out (x, y) (3)

  Next, the error diffusion unit 807 distributes the error e (x, y) based on a preset diffusion coefficient and adds it to the error data E (x, y) stored in the error memory 806. . Here, for example, when the coefficient as shown in FIG. 9 is used as the diffusion coefficient, the error diffusion unit 807 performs the following processing.

E (x + 1, y) = E (x + 1, y) + e (x, y) × (−3) / 16
(4)
E (x + 2, y) = E (x + 2, y) + e (x, y) × 7/16
(5)
E (x−2, y + 1) = E (x−2, y + 1) + e (x, y) × 2/16
(6)
E (x-1, y + 1) = E (x-1, y + 1) + e (x, y) * (-1) / 16
(7)
E (x, y + 1) = E (x, y + 1) + e (x, y) × (−3) / 16
(8)
E (x + 1, y + 1) = E (x + 1, y + 1) + e (x, y) × (−1) / 16
(9)
E (x + 2, y + 1) = E (x + 2, y + 1) + e (x, y) × 2/16
(10)
E (x−2, y + 2) = E (x−2, y + 2) + e (x, y) × 5/16
(11)
E (x-1, y + 2) = E (x-1, y + 2) + e (x, y) * 2/16
(12)
E (x, y + 2) = E (x, y + 2) + e (x, y) × 3/16
(13)
E (x + 1, y + 2) = E (x + 1, y + 2) + e (x, y) × 2/16
(14)
E (x + 2, y + 2) = E (x + 2, y + 2) + e (x, y) × 1/16
(15)

  Error data generated by the error diffusion process is stored in the error memory 806.

  As described above, the error diffusion processing in the image processing unit is performed by the configuration of FIG.

  Next, the reason why isolated dot generation can be suppressed by error diffusion processing by such processing will be described.

  In error diffusion, when dots are output, the dots are dispersed according to the density by diffusing the quantization error to surrounding pixels. Therefore, many isolated dots are generated. For example, when the coefficient as shown in FIG. 9 is used as the diffusion coefficient, when the dot of the target pixel becomes On in the highlight portion, the error e (x, y) generated at the target pixel position becomes negative. Diffuse negative errors to surrounding pixels. Therefore, it is difficult for dots to be generated in the peripheral pixels.

  On the other hand, if the coefficient in the vicinity of the target pixel as shown in FIG. 9 is error-diffused with a negative coefficient, if the dot of the target pixel becomes On, the error e (x, y) is negative, but since the coefficient in the vicinity of the target pixel is negative, a positive error is diffused in the vicinity of the target pixel by the product of negative and negative, and a negative error is diffused in the peripheral pixels. Therefore, since a negative error is not diffused in the vicinity of the target pixel, the dot is likely to be turned on and a cluster is easily formed.

  Further, when the dot of the target pixel is turned off, the error e (x, y) generated at the target pixel position is positive, but the coefficient near the target pixel is negative, so that a negative error is diffused near the target pixel. Therefore, the neighboring pixels where the dot of the target pixel is turned off are also likely to be turned off. As described above, the dots On are easily gathered in the highlight portion and the dots Off are easily gathered in the dark portion.

  Here, the error e (x, y) generated at the target pixel position is negative, and a positive error is diffused in the vicinity of the target pixel. However, there are many peripherals including the positive error diffused in the vicinity of the target pixel. There is no problem because negative errors are diffused to the artist. Note that the total value of the coefficients shown in FIG. If the total value of the coefficients is 1, the image obtained by the error diffusion process is equivalent to the density of the input image, that is, the density is stored.

  The reproducibility varies depending on the image recording apparatus 103. In such a case, the cluster size of the dot On or Off may be changed according to the degree of dot variation. For such a problem, the absolute value of the negative coefficient near the target pixel may be increased, or the absolute value of the positive coefficient far from the target pixel may be increased. Since the coefficient in the vicinity of the pixel of interest takes a negative value, the difference from the distant coefficient increases, so that it becomes easy to form a cluster, and the cluster size can be increased without increasing the error diffusion matrix size. Needless to say, the cluster size can be increased by increasing the range of the negative coefficient in the vicinity of the target pixel.

  When the coefficients as shown in FIG. 9 are used, the negative coefficients diffused to the adjacent pixels in the main scanning direction and the sub scanning direction with respect to the target pixel are the same. Now, if the absolute value of the coefficient for the pixel adjacent in the main scanning direction is made larger than the absolute value of the coefficient for the pixel adjacent in the sub-scanning direction, a cluster that is likely to be adjacent in the main scanning direction can be formed. Similarly, if the absolute value of the coefficient for the pixel adjacent in the sub-scanning direction is made larger than the absolute value of the coefficient for the pixel adjacent in the main scanning direction, a cluster that is likely to be adjacent in the sub-scanning direction can be formed.

  When clusters that are likely to be adjacent in the main scanning direction are formed, depending on the image, the dots may be biased to odd or even rows. Therefore, in a multi-beam printer, it is preferable to use LDs evenly by forming clusters that are easily adjacent in the sub-scanning direction. Similarly, when clusters that are likely to be adjacent in the sub-scanning direction are formed, depending on the image, the dots may be biased toward odd or even rows. In an LED array type printer, it is preferable to form a cluster that is likely to be adjacent in the main scanning direction and use the LEDs equally.

  Although the present invention is for error diffusion processing, it can be similarly applied to the minimum average error method.

  Note that the present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, and a printer), and a device (for example, a copying machine and a facsimile device) including a single device. You may apply to.

  Another object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and a computer (CPU or MPU) of the system or apparatus stores the storage medium. Needless to say, this can also be achieved by reading and executing the stored program code. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment.

  As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) operating on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion board is based on the instruction of the program code. Needless to say, the CPU of the function expansion unit or the like performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  As is apparent from the above description, according to the present embodiment, isolated dot generation can be suppressed, and abnormal image suppression can be realized at low cost by the multi-beam method and the LED array method.

  Further, the multi-value (M value) image data is quantized into N values (M> N ≧ 2) using an error diffusion method or an average error minimum method, and recording is performed using dots corresponding to the N values. In the image processing apparatus, the error diffusion matrix can solve the problem of isolated dots by setting the diffusion coefficient of the neighboring pixels of the target pixel to 0 or less, and an output image result with good image quality can be obtained. .

  In addition, by setting the error diffusion matrix to be negatively larger as the diffusion coefficient of the pixel closer to the target pixel, the problem of isolated dots occurring can be solved, and an output image result with good image quality can be obtained.

  In addition, the error diffusion matrix is set so that the diffusion coefficient of adjacent pixels in the main scanning direction is negatively larger than the diffusion coefficient of adjacent pixels in the sub-scanning direction, so that dots are easily connected in the main scanning direction. Output image results with good image quality can be obtained.

  In addition, the error diffusion matrix is set so that the diffusion coefficient of adjacent pixels in the sub-scanning direction is negatively larger than the diffusion coefficient of adjacent pixels in the main-scanning direction, so that dots are easily connected in the sub-scanning direction. Output image results with good image quality can be obtained.

  In addition, by setting the sum of all coefficients to 1 in the error diffusion matrix, the image obtained by error diffusion can store the density of the original image.

  The embodiment of the present invention has been described above. The above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto, and various modifications can be made without departing from the scope of the invention. .

It is a figure which shows the block configuration of the image processing apparatus in embodiment of this invention. It is a figure which shows the structure of the image recording apparatus in embodiment of this invention. It is a perspective view which shows an example of the positional relationship of a light beam and a photoconductive drum. It is a figure which shows the structure of a LED array optical system unit. It is explanatory drawing which shows arrangement | positioning of each light emitting diode D on a LED array. It is a figure which shows the structure of a LED array optical system unit. It is a figure which shows the structure of a LED array optical system unit. It is a block diagram which shows the structure of the image processing apparatus in embodiment of this invention. It is a figure which shows an example of a spreading | diffusion coefficient. It is a figure which shows an example of a spreading | diffusion coefficient.

Explanation of symbols

801 Input terminal 802 Adder 803 Comparison determination unit 804 Output terminal 805 Subtractor 806 Error memory 807 Error diffusion unit

Claims (9)

Multi-value (M value) image data is quantized into N values (M> N ≧ 2) using an error diffusion method or an average error minimum method, and recording is performed using dots corresponding to the N values. A processing device comprising:
An image processing apparatus characterized in that the error diffusion matrix has a diffusion coefficient of 0 or less for pixels in the vicinity of the target pixel.   2. The image processing apparatus according to claim 1, wherein the error diffusion matrix is negatively larger as a diffusion coefficient of a pixel closer to the target pixel.   The image processing apparatus according to claim 1, wherein the error diffusion matrix has a diffusion coefficient of adjacent pixels in the main scanning direction that is negatively larger than a diffusion coefficient of adjacent pixels in the sub-scanning direction.   The image processing apparatus according to claim 1, wherein the error diffusion matrix has a diffusion coefficient of adjacent pixels in the sub-scanning direction that is negatively larger than a diffusion coefficient of adjacent pixels in the main scanning direction.   4. The image processing apparatus according to claim 1, wherein dots are easily connected in the main scanning direction in LED array type electrophotography.   5. The image processing apparatus according to claim 1, wherein dots are easily connected in the sub-scanning direction in multi-beam electrophotography.   The image processing apparatus according to claim 1, wherein the error diffusion matrix has a total of 1 for all coefficients.   An image recording apparatus having a function of each unit of the image processing apparatus according to claim 1. The program for making a computer implement | achieve the function of each means of the image processing apparatus of any one of Claims 1 thru | or 7.

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