JP2010050708A - Image processor, image processing method, image forming apparatus, program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make density deterioration due to a halo phenomenon more inconspicuous. <P>SOLUTION: A rendering part 301 converts a drawing instruction from an application into image data for one page to be expressed by pixel values from zero to 255. An image input part 302 stores the image data from the rendering part 301 to output the pixel value of a pixel position to be requested from an image correction part 303. The image correction part 303 sequentially considers each pixel of an input image as a noticing pixel, and when the noticing pixel is the one whose density is deteriorated by the halo phenomenon, raises the pixel value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image processing method, an image forming apparatus, a program, and a recording medium that make a halo phenomenon inconspicuous, and relates to an image forming apparatus such as a printer and a copying machine, in particular, an image forming apparatus that performs output by electrophotography. It relates to a technique suitable for the above.

  In order to make the halo phenomenon in which the density of the background of the character or solid image decreases when forming a high-density character or solid image on the halftone background image, the following technology is used. Proposed.

  For example, Patent Document 1 discloses an image forming system that suppresses the generation of a halo image by appropriately setting the linear velocity ratio of the developer bearing member to the image bearing member. In order to prevent the density of the low density portion from decreasing when the output image changes from the low density portion to the high density portion in the main / sub scanning direction, the low density pixel value is increased from the low density pixel value in the main / sub scanning direction. An image forming apparatus that extracts edge pixels that change to density pixel values and corrects the pixel values of pixels having low density pixel values of input image data based on the positions and pixel values of the extracted edge pixels. Has been.

JP 2004-109519 A Japanese Patent No. 3832521

  However, in Patent Document 1 described above, the halo phenomenon that occurs in the direction orthogonal to the rotation direction of the image carrier or developer carrier cannot be reduced.

  By the way, there are cases where the amount of decrease in density and the area of the area where the density is lowered differ depending on whether the high density area is wide or narrow. That is, the density reduction in the halftone background area 102 that is in the vicinity of the high density area 101 in FIG. 1A and the vicinity of the high density area 201 in FIG. However, in the above-mentioned Patent Document 2, since the correction amount is determined based on the distance from the edge pixel, a difference is added to both. Therefore, the halo phenomenon cannot be appropriately reduced.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an image processing apparatus, an image processing method, an image forming apparatus, a program, and a recording medium that make density reduction due to a halo phenomenon less noticeable. Is to provide.

  The present invention provides a correction value determining means for determining a correction value for each pixel of interest using the pixel of the input image data as the pixel of interest, and after correcting the pixel of interest using the correction value and the pixel value of the pixel of interest as variables. Correction means for calculating a pixel value, wherein the correction value determination means refers to a pixel value of a peripheral pixel of the target pixel, and the pixel value of the peripheral pixel is a predetermined amount with respect to the pixel value of the target pixel. In the case where the value represents a high density as described above, it is most important that the difference between the pixel value of the peripheral pixel and the pixel value of the target pixel and the value corresponding to the pixel value of the target pixel are integrated to obtain a correction value. Features.

  Claims 1 and 8 to 11: Pixel values that are expected to be output darker for pixels in which density reduction due to the halo phenomenon is expected can be corrected in advance, and density reduction due to the halo phenomenon can be made inconspicuous. .

  According to the second aspect of the present invention, since the process is not performed on the pixel in which the density reduction due to the halo phenomenon is not conspicuous, the image quality deterioration due to the correction process can be suppressed.

  According to the third aspect of the present invention, since processing is not performed on low-density or high-density pixels in which density reduction due to the halo phenomenon is not noticeable, image quality deterioration due to correction processing can be suppressed.

  Claim 4: Discontinuity of correction processing at the boundary between a pixel where density reduction due to the halo phenomenon is not noticeable and a pixel where density reduction due to the halo phenomenon is expected can be alleviated, and image quality deterioration due to correction processing can be suppressed. be able to.

  Claim 5: Since it is possible to detect a pixel in which a decrease in density due to the halo phenomenon is expected, the decrease in density due to the halo phenomenon can be made inconspicuous.

  According to the sixth aspect of the present invention, since the correction processing amount for the pixel in which the density reduction due to the halo phenomenon is expected can be calculated with a low load, the density reduction due to the halo phenomenon can be made inconspicuous at a low load.

  Claim 7: Since it is possible to set an appropriate correction parameter for the difference in the screen to be used in which the degree of the halo phenomenon is expected to be different, the decrease in density due to the halo phenomenon can be made inconspicuous.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the pixel value takes an integer value of 0 or more and 255 or less, and the higher the value, the higher the density.

Example 1
FIG. 2 shows the configuration of the image forming apparatus according to the first embodiment of the present invention. In FIG. 2, the rendering unit 301 converts a drawing command from an application (not shown) into image data for one page represented by pixel values of pixels 0 to 255. The image input unit 302 stores the image data received from the rendering unit 301 and outputs the pixel value at the pixel position requested from the image correction unit 303.

  The image correcting unit 303 sends the image data to the subsequent processing while converting the image data for one page so as to make the halo phenomenon inconspicuous by a method described later. The halftone processing unit 304 converts the image data for one page from the image correction unit 303 into image data that can be expressed by the output device, and sends the image data to subsequent processing. For example, when the output device can take only two values of 0 or 255 per pixel, that is, whether the dot is hit or not, the average value of the pixel values of the input image and the pixel value after halftone processing Conversion processing is performed so that the average value of the two becomes substantially the same. An example of the conversion process used here is a dithering process, which compares a predetermined threshold value for each pixel position with a pixel value, and outputs 255 if the pixel value is greater than the threshold value, and outputs 0 if not. To do.

  The image output unit 305 represents the image data on paper by an output device using an electrophotographic method based on the image data received from the halftone processing unit 304.

  FIG. 3 is a flowchart of processing executed by the image correction unit 303. The image correction unit 303 sequentially sets each pixel of the input image as a pixel of interest, and increases the pixel value when the pixel of interest is a pixel whose density decreases due to the halo phenomenon.

  The pixel value of the target pixel is substituted into the variable value (S0401). It is determined whether or not the value satisfies the condition A (S0402). Here, the condition A is a condition indicating that the pixel of interest is a pixel value that is conspicuous when the density is lowered due to the halo phenomenon, and further when the density is lowered. In this embodiment, the condition A is 40 or more and 210 or less. Let it be a pixel value. This is because when the pixel value is high or low, the density does not decrease or does not appear even if the pixel value occurs, and conversely, the density change caused by performing this correction processing causes a sense of incongruity. This is because correction processing is performed only when the value is an intermediate value. If the condition A is true, the process proceeds to S0403, and if the condition A is false, the process using the pixel as the target pixel is terminated.

  Next, the increment value of the pixel of interest based on the pixel value distribution in the main scanning direction is calculated by a method described later (S0403). Similarly, the increment value of the pixel of interest based on the pixel value distribution in the sub-scanning direction is calculated (S0404). The larger of the increment value obtained in S0403 and the increment value obtained in S0404 is adopted as the increment value (S0405).

  When the value is condition A ', the increment value is corrected (S0406). Here, the condition A ′ is near both ends of the condition A, and the increment value is corrected in order to suppress a change in the output image due to abrupt switching between the execution and non-execution of the correction process. In this embodiment, it is assumed that the condition A ′ is a pixel value from 40 to 49, or from 201 to 210. When the pixel value is 40 or more and 49 or less, or 201 or more and 210 or less, as shown in FIG. 4, the pixel value is away from 50 in the former case, and from 100% to 0% as it is away from 200 in the latter case. Multiply the multiplier by a factor that approaches.

  Next, the increment value determined in S0405 or the increment value corrected in S0406 is added to the pixel value of the target pixel (S0407). The processing from S0401 to S0407 is sequentially performed for all input pixels.

  FIG. 5 shows a detailed processing flowchart of S403 and S404 for calculating the increment value of the target pixel based on the pixel value distribution in the main scanning direction or the sub-scanning direction.

  First, one unselected pixel is selected from the peripheral pixels of the target pixel (S601). The range of the peripheral pixels is determined based on the maximum range in which the high density pixel has an effect of density reduction due to the halo phenomenon.

  In the present embodiment, when the image of FIG. 1A is output, the processing corresponds to the output condition in which the halo phenomenon as shown in FIG. That is, the density reduction region 1501 is both the front and rear of the high density region 101 in the main scanning direction (left and right in FIG. 1C) and the front side in the sub scanning direction (upper side in FIG. 1C). In order to recognize, the range of surrounding pixels is determined.

  When calculating an increment value based on the pixel value distribution in the main scanning direction, a rectangular area 702 in the main scanning direction 31 dots and the sub scanning direction 11 dots is set as a peripheral pixel around 701 shown in FIG. .

  Similarly, when calculating the increment value based on the pixel value distribution in the sub-scanning direction, the surrounding area, the rectangular area 802 in the main scanning direction 11 dots and the sub-scanning direction 20 dots is set as the surrounding area with 801 shown in FIG. Let it be a pixel.

  Next, the pixel value of the selected peripheral pixel is substituted into the variable target (S602). Next, the degree of influence delta received from the selected peripheral pixel is calculated by a method described later (S603). If all the peripheral pixels have not been selected, the process returns to S601 to perform processing for the next peripheral pixel. If all the peripheral pixels have been selected, the process proceeds to S605 (S604).

  Next, the sum total of the degree of influence delta received from each peripheral pixel is calculated (S605). Next, an increment value of the target pixel is calculated from the sum of the influence levels delta by a method described later (S606).

  FIG. 7 shows a detailed processing flowchart of S603 for calculating the degree of influence delta received from the selected peripheral pixels. First, 0 is substituted for the influence delta (S901). Next, it is determined whether or not the difference between the target, which is the pixel value of the selected peripheral pixel, and the value, which is the pixel value of the target pixel, satisfies the condition B (S902).

  Condition B is a condition for determining whether the selected peripheral pixel is a high-density pixel that causes a halo phenomenon in the target pixel, and is true when the value obtained by subtracting value from target is equal to or greater than the constant thresh. , Otherwise false. In this embodiment, the constant thresh is 60.

  If the determination result is true, the process proceeds to S903. If the determination result is false, the value 0 assigned to the variable delta in S901 is valid as it is. When the pixel value of the target pixel p and its peripheral pixels a, b, c, and d are the values shown in FIG. 8A, the peripheral pixel a whose pixel value is greater than or equal to thresh than the pixel value p of the target pixel p True in d, false in b and c (S902).

  The value of (target-value) / thresh is substituted for delta. As a result, the delta value increases as the pixel value of the peripheral pixel is larger than the pixel value of the target pixel (S903).

  Next, when the difference between the target and the value is the condition B ′, the delta is corrected according to the difference. Here, the condition B ′ is a condition that the difference is close to thresh, and the delta is greatly different due to a slight difference in the pixel value of the pixel of interest and the pixel values of the peripheral pixels. To do.

  In this embodiment, it is assumed that the condition B ′ is 50 or more and 59 or less, and when the difference between the target and value is 50 or more and 59 or less, 100% as the difference increases from 60 as shown in FIG. The multiplication factor that approaches 0% is multiplied by delta (S904).

  Next, if delta is equal to or greater than a predetermined value a, a is substituted into delta. That is, when delta exceeds a predetermined value a, the value is stored in a. A is a set of a pixel value of the high density portion targetM and a pixel value valueM of the halftone background when the halo is most noticeable. From (targetM-valueM) / thresh.

  In this embodiment, when the pixel value of the high density portion is 255 and the pixel value of the halftone background portion is 102, the halo is most noticeable, and the predetermined value a is 2.55 (S905).

  FIG. 9 shows a detailed processing flowchart of S606 in which the increment value of the target pixel is calculated from the sum of the influence degrees delta. First, a value obtained by multiplying the sum of the influence levels delta by a predetermined value b is set as an increment value. A method for setting the predetermined value b will be described later (S1201).

  Next, if the increment value is equal to or greater than the predetermined value c, c is substituted. The predetermined value c is the maximum value of the increment value of the target pixel. It is set based on the density range that decreases due to the halo phenomenon, and is set to 30 in this embodiment (S1202). When the increment value of the pixel of interest is calculated based on the pixel value distribution in the sub-scanning direction, the increment value becomes the predetermined value c when the delta is the maximum value delta of all peripheral pixels. Set as follows. In the present embodiment, as shown in FIG. 6B, the total number of surrounding pixels is 220 pixels of 20 × 11, so the predetermined value b is set as c ÷ a ÷ 220.

  Further, when the increment value of the target pixel is calculated based on the pixel value distribution in the main scanning direction, the increment value is predetermined when the delta is the maximum value delta at half of all the peripheral pixels. Set to value c. In this embodiment, as shown in FIG. 6A, the total number of surrounding pixels is 340 pixels of 31 × 11−1, and therefore the predetermined value b is set as c ÷ a ÷ 340. The reason why the value obtained by multiplying the total value of the influence levels delta when the predetermined value a having the maximum value of delta in half of all peripheral pixels is multiplied by the predetermined value b is set to the predetermined value c is that the main scanning This is because the increment value is close to the predetermined value c when the predetermined value a having the maximum value of delta is obtained for all peripheral pixels only on the front side in the direction or only on the rear side in the main scanning direction.

  As described above, when the pixel value distribution in the main scanning direction is as shown in FIG. 10A, the image correction unit 303 converts the pixel value distribution into the distribution shown in FIG.

Example 2
FIG. 11 shows a configuration of an image forming apparatus according to Embodiment 2 of the present invention. Hereinafter, the difference from the first embodiment will be mainly described. The screen determination unit 1601 sends the number of screen lines to be used to the image correction unit 1602 and sends the threshold value of the screen to be used to the halftone processing unit 1603 based on a setting by a user (not shown).

  The image correction unit 1602 refers to the peripheral area corresponding to the number of screen lines to be used, and performs processing using the parameters shown in FIG.

  If the number of lines on the screen is less than 170 lines, the area to be referenced is 1801 shown in FIG. 13 (a) when the increment value based on the pixel value distribution in the main scanning direction is calculated. A rectangular area 1802 having a scanning direction of 15 dots and a sub-scanning direction of 5 dots is set as a peripheral pixel. Similarly, when calculating the increment value based on the pixel value distribution in the sub-scanning direction, the surrounding area, the rectangular area 1902 of the main scanning direction 7 dots and the sub-scanning direction 10 dots around 1901 shown in FIG. Let it be a pixel.

  If the number of lines on the screen is 170 lines or more, when calculating an increment value based on the pixel value distribution in the main scanning direction, 701 shown in FIG. A rectangular area 702 in the sub scanning direction 11 dots is set as a peripheral pixel. Similarly, when calculating an increment value based on the pixel value distribution in the sub-scanning direction, a pixel 801 shown in FIG. 6B is used as a pixel of interest, and the surrounding area, a rectangular region 802 in the main scanning direction 11 dots and the sub-scanning direction 20 dots is set as the peripheral pixels. And

  The determination of these peripheral areas and parameters is made, for example, for the low line number screen of less than 170 lines, with the optimum conditions experimentally obtained with a 141 line screen of less than 170 lines, and a high line number screen of 170 lines or more. In this case, the optimum condition is experimentally obtained with a 212-line screen having 170 lines or more. Experiments have shown that the halo phenomenon becomes more pronounced as the number of screen lines increases. The halftone processing unit 1603 generates an image using the screen sent from the screen determination unit 1601.

Example 3
FIG. 14 is a diagram for explaining an image forming method according to Embodiment 3 of the present invention. Hereinafter, the difference from the first embodiment will be mainly described. In the image correction unit 303, when calculating an increment value based on the pixel value distribution in the main scanning direction, 2001 shown in FIG. 14 is used as a pixel of interest, and the surrounding area, the main scanning direction 15 dots, and the sub scanning direction 5 dots are rectangular areas. The influence delta and the increment value of the target pixel are calculated using 24 pixels indicated by shading including 2002 pixels as peripheral pixels.

  This reference pixel decimation reduces the number of peripheral pixels to be referenced from 74 pixels to 24 pixels. Similarly, when calculating an increment value based on a pixel value distribution in the sub-scanning direction, the number of peripheral pixels to be referenced can be reduced by thinning out the reference pixels.

  In addition, the present invention supplies a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and the computer (CPU or MPU) of the system or apparatus is stored in the storage medium. It is also achieved by reading and executing the program code. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments. As a storage medium for supplying the program code, for example, a hard disk, an optical disk, a magneto-optical disk, 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 an instruction of the program code. A case where part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing is also 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 is performed based on the instruction of the program code. This includes the case where the CPU or the like provided in the board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing. Further, the program for realizing the functions and the like of the embodiments of the present invention may be provided from a server by communication via a network.

It is a figure explaining the conventional subject. 1 illustrates a configuration of an image forming apparatus according to a first exemplary embodiment. It is a process flowchart of an image correction part. The multiplication factor of the increment value according to value is shown. The processing flowchart which calculates the increment value of an attention pixel is shown. The surrounding pixels in the case of calculating the increment value are shown. The processing flowchart which calculates influence degree delta is shown. It is a figure explaining the process of S902 and S904 of FIG. 5 shows a processing flowchart for calculating an increment value of a pixel of interest from the sum of influence degrees delta. The pixel value distribution before correction | amendment and the pixel value distribution after correction | amendment by Example 1 are shown. 2 illustrates a configuration of an image forming apparatus according to a second exemplary embodiment. The parameter which the image correction part of Example 2 uses is shown. The surrounding pixels in the case of calculating the increment value of Example 2 are shown. FIG. 10 is a diagram illustrating an image forming method according to a third embodiment.

Explanation of symbols

301 Rendering unit 302 Image input unit 303 Image correction unit 304 Halftone processing unit 305 Image output unit

Claims (11)

  A correction value determining means for determining a correction value for each pixel of interest using the pixel of the input image data as a pixel of interest, and a pixel value after correction of the pixel of interest using the correction value and the pixel value of the pixel of interest as variables The correction value determining means refers to a pixel value of a peripheral pixel of the target pixel, and the pixel value of the peripheral pixel has a higher density than the pixel value of the target pixel by a predetermined amount or more. An image processing apparatus characterized in that, when the value is a value to be expressed, the difference between the pixel value of the peripheral pixel and the pixel value of the target pixel and a value corresponding to the pixel value of the target pixel are integrated to obtain a correction value .   The image processing apparatus according to claim 1, wherein the correction is not performed when a pixel value of the target pixel is in a predetermined range.   The image processing apparatus according to claim 2, wherein the predetermined range is a low density portion and a high density portion.   4. The image processing according to claim 2, wherein when the pixel value of the target pixel is in the vicinity of the predetermined range, the correction value gradually approaches 0 as the pixel value of the target pixel approaches the predetermined range. apparatus.   The correction value determining unit determines a correction value corresponding to each reference area for at least a reference area wide in the main scanning direction and a reference area wide in the sub-scanning direction, and corresponds to each determined reference area. The image processing apparatus according to claim 1, wherein a maximum correction value is determined as a correction value for the target pixel.   The image processing apparatus according to claim 1, wherein the correction value determining unit thins out and uses the pixel values of the peripheral pixels.   The image processing apparatus according to claim 1, wherein the correction value determining unit changes a peripheral pixel area to be referred to according to the number of screen lines to be used.   In an image forming apparatus that performs output using an electrophotographic method, a correction value determining unit that determines a correction value for each pixel of interest using a pixel of input image data as a pixel of interest, and a variable between the correction value and the pixel value of the pixel of interest Correction means for calculating a corrected pixel value of the target pixel as the correction value determining means, referring to the pixel values of the peripheral pixels of the target pixel, and the pixel values of the peripheral pixels being the target pixel The number of peripheral pixels, which is a value representing a high density of a predetermined amount or more with respect to the pixel value, is obtained, and the correction value is obtained by integrating the number of pixels and the pixel value of the target pixel. Image forming apparatus.   Using the pixel of the input image data as the target pixel, a correction value determining step for determining a correction value for each target pixel, and calculating the corrected pixel value of the target pixel using the correction value and the pixel value of the target pixel as variables The correction value determining step refers to the pixel value of the peripheral pixel of the target pixel, and the pixel value of the peripheral pixel has a higher density than the pixel value of the target pixel by a predetermined amount or more. And a correction value by adding a value corresponding to the difference between the pixel value of the peripheral pixel and the pixel value of the target pixel and the pixel value of the target pixel. .   A program for causing a computer to implement the image processing method according to claim 9.   A computer-readable recording medium on which a program for causing a computer to implement the image processing method according to claim 9 is recorded.

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