JP2010045488A - Image forming apparatus and data compression method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and a data compression method for suppressing the degradation of quality in an image formed on a sheet of paper without changing the number of pixels constituting the image. <P>SOLUTION: A control unit 400 provided on the image forming apparatus 100 has a calculating section 441 constituting one set pixel of interest by a plurality of adjacent pixels and calculating the value of the set pixel of interest involving first depiction data based on values of the plurality of adjacent pixels involving the first depiction data, a compression section 442 encoding the value of the set pixel of interest involving the first depiction data, a distribution section 443 distributing an error or a difference between the value of the set pixel of interest involving the first depiction data and an expansion value of the set pixel of interest involving the second depiction data to peripheral pixels around the set pixel of interest and a shift section 444 repetitively shifting the set pixel of interest until compression of the first depiction data is completed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet, and a data compression method that compresses first drawing data into second drawing data.

  2. Description of the Related Art Conventionally, an image forming apparatus such as a copying machine or a printer that forms an image on a sheet based on image data is known. When the image forming apparatus is a copying machine, the image forming apparatus acquires image data as drawing data by reading an image from a document. On the other hand, when the image forming apparatus is a printer, the image forming apparatus acquires image data as drawing data or original data for generating drawing data from an external device such as a personal computer.

  When acquiring original data from an external device such as a personal computer, the external device outputs a print job described in a page description language (PDL). The print job includes image data described in a page description language. The image data described in the page description language is, for example, the first drawing data described in an intermediate language such as bitmap data by a printer controller that is configured separately from the printer or incorporated in the printer. Converted. In the first drawing data, one pixel is represented by the first number of bits, for example, 8 bits. That is, in the first drawing data, one pixel has 256 gradations.

  On the other hand, the image forming apparatus obtains second drawing data by reducing the gradation of the first drawing data due to restrictions on the size of the memory area and the drive control capability of the laser. In the second drawing data, one pixel is represented by a second bit number smaller than the first bit number, for example, one bit. That is, in the second drawing data, typically, one pixel has two gradations.

  In the second drawing data, the second bit number is not limited to 1 bit, and may be 2 bits if the size of the memory area and the laser drive control capability allow. In such a case, one pixel is expressed by two bits, and one pixel has four gradations.

As described above, the gradation reproducibility deteriorates as the gradation of the first drawing data is lowered. On the other hand, in order to suppress deterioration in gradation reproducibility, a technique has been proposed in which one pixel constituting the input image is represented by a plurality of pixels constituting the output image (for example, Patent Document 1). ). However, this technique is applicable only to the case where the number of pixels of the input image is smaller than the number of pixels of the output image, that is, the case where the output image has a lower resolution than the input image.
JP-A-8-234705

  As described above, the technique of Patent Document 1 is based on the premise that the number of pixels of the input image is smaller than the number of pixels of the output image. Specifically, the number of pixels in the output image must be an integer multiple of the number of pixels in the input image.

  Further, as a background technique different from the above-described Patent Document 1, it is known to reduce the resolution by using an error diffusion method. In the error diffusion method, it is possible to reduce the occurrence of fringe interference caused by superposition of regular patterns, so-called “moire”. However, in an area where the change in density is small, an unsightly striped pattern may occur even if the error diffusion method is used.

  Therefore, the present invention has been made to solve the above-described problems, and an image forming apparatus and data that can suppress deterioration in the quality of an image formed on a sheet without reducing the resolution. An object is to provide a compression method.

  The image forming apparatus according to the first feature forms an image on a sheet. The image forming apparatus compresses the first drawing data into second drawing data, expands the second drawing data into decompressed drawing data, and controls the control unit 400 according to an instruction from the control unit. An image forming unit (image forming unit 50) that forms an image on a sheet based on the decompressed drawing data. The control unit configures one target set pixel by a plurality of adjacent pixels, and determines the target set pixel of the first drawing data based on the values of the plurality of adjacent pixels of the first drawing data. A calculation unit (calculation unit 441) that calculates a value is compared with the value of the target set pixel related to the first drawing data and a determination threshold, and the value of the target set pixel related to the first drawing data is encoded An error that is a difference between the compression unit (compression unit 442) that converts the value of the target set pixel related to the first drawing data and the expansion value of the target set pixel related to the second drawing data A distribution unit (distribution unit 443) that distributes to peripheral pixels provided around the pixel and corrects the value of the peripheral pixel related to the first drawing data by the error, and finishes the compression of the first drawing data Until the plurality By shifting the pixel to be the eye, and a shift unit (shift section 444) repeating the shift of the target set pixel. The calculation unit, the compression unit, and the distribution unit repeat processing for each shift of the plurality of pixels of interest.

  According to this feature, the control unit configures one target set pixel by a plurality of adjacent pixels, and encodes the value of the target set pixel related to the first drawing data. That is, the control unit compresses the first drawing data into the second drawing data in units of attention set pixels.

  Thus, the value of the target set pixel related to the second drawing data can be expressed by the number of bits assigned to the plurality of adjacent pixels constituting the target set pixel. That is, by increasing the number of bits representing the value of the target collection pixel related to the second drawing data, it is possible to increase the number of gradations of the pixel related to the decompressed drawing data.

  As described above, in the case of using the error diffusion method, the number of gradations of the pixels can be increased without reducing the compression rate, so that deterioration of the quality of the image formed on the paper can be suppressed. Of course, it is not necessary to reduce the resolution.

  In the first feature, the calculation unit calculates an average value of the values of the plurality of adjacent pixels related to the first drawing data as a value of the target set pixel related to the first drawing data.

  In the first feature, the number of the plurality of adjacent pixels constituting the target set pixel includes a compression rate for compressing the first drawing data into the second drawing data, and one pixel related to the decompressed drawing data. It is determined by the number of gradations.

  The data compression method according to the second feature compresses the first drawing data into the second drawing data. In the data compression method, one target set pixel is configured by a plurality of adjacent pixels, and the target set pixel of the first drawing data is determined based on the values of the plurality of adjacent pixels of the first drawing data. Step A for calculating a value, Step B for comparing the value of the target set pixel related to the first drawing data with a determination threshold, and encoding the value of the target set pixel, and the first drawing data An error, which is a difference between the value of the target set pixel and the expanded value of the target set pixel related to the second drawing data, is distributed to peripheral pixels provided around the target set pixel, and the first drawing The shift of the target set pixel is repeated by correcting the value of the surrounding pixels related to the data by the error and shifting the plurality of target pixels until the compression of the first drawing data is completed. And a step D to return. Step A, Step B and Step C are repeated for each shift of the plurality of pixels of interest.

  According to the present invention, it is possible to provide an image forming apparatus and a data compression method that can suppress deterioration in quality of an image formed on a sheet without reducing the resolution.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

  However, it should be noted that the drawings are schematic and ratios of dimensions and the like are different from actual ones. Therefore, specific dimensions and the like should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

[First Embodiment]
(Outline of image forming apparatus)
The outline of the image forming apparatus according to the first embodiment will be described below with reference to the drawings. FIG. 1 is a diagram schematically illustrating an image forming apparatus 100 according to the first embodiment. In FIG. 1, it should be noted that the detailed configuration of the image forming apparatus 100 is omitted.

  As shown in FIG. 1, the image forming apparatus 100 includes an automatic document feeding unit 10, an image reading unit 20, a paper tray unit 30, a paper feeding unit 40, an image forming unit 50, a fixing unit 60, a discharge unit. A paper unit 70, a reversing unit 80, and an operation unit 90 are provided. The image forming apparatus 100 further includes a paper feeding device 200 and a post-processing device 300.

  The image forming apparatus 100 is connected to a user terminal 600 via a printer controller 500. For example, the image forming apparatus 100 is connected to the printer controller 500 by a video bus 501. For example, the printer controller 500 is connected to the user terminal 600 via a LAN (Local Area Network) 601.

  In the first embodiment, as the image forming apparatus 100, an MFP (Multiple Function Peripheral) that forms an image on a sheet by an electrophotographic method is exemplified. However, the image forming method is not limited to the electrophotographic method, and may be an ink jet method, a thermal transfer method, a dot impact method, or the like.

  The automatic document feeder unit 10 is a unit that conveys a document to be copied. The image reading unit 20 is a unit that reads an image of a document and generates image data.

  The paper tray unit 30 is a unit that stores paper. The paper feed unit 40 is a unit that feeds paper to the image forming unit 50.

  The image forming unit 50 forms a toner image on a sheet fed by the sheet feeding unit 40 in accordance with the image data generated by the image reading unit 20. Specifically, the image forming unit 50 forms a yellow unit 50Y for forming a toner image corresponding to yellow, a magenta unit 50M for forming a toner image corresponding to magenta, and a toner image corresponding to cyan. It includes a cyan unit 50C, a black unit 50K that forms a toner image corresponding to black, an intermediate transfer belt 51, and a transfer roller 52. Each of the yellow unit 50Y, the magenta unit 50M, the cyan unit 50C, and the black unit 50K includes a photosensitive drum and a writing processing unit.

  Each photosensitive drum is a drum having a photoconductive photosensitive layer formed on the surface thereof, and is rotatably provided. An electrostatic charge latent image corresponding to each color is formed on the surface of each photosensitive drum.

  Each writing processing unit forms an electrostatic latent image corresponding to each color on the surface of the photosensitive drum in accordance with image data acquired from a control unit 400 described later, that is, second drawing data described later. Specifically, the writing processing unit includes a laser diode that emits laser light based on image data, and a scanning optical unit that deflects and scans the laser light.

  The intermediate transfer belt 51 is wound around a plurality of rollers so as to pass through the yellow unit 50Y, the magenta unit 50M, the cyan unit 50C, the black unit 50K, and the transfer roller 52. On the intermediate transfer belt 51, toner images of respective colors are superimposed.

  Specifically, the transfer roller 52 transfers the toner image formed on the intermediate transfer belt 51 onto a sheet, and the transfer roller 52 is charged so as to have a polarity opposite to that of the toner.

  The fixing unit 60 is a unit that fixes a toner image formed on a sheet to the sheet by thermocompression bonding. The paper discharge unit 70 is a unit for discharging the paper on which the toner image is fixed. The reversing unit 80 is a unit that reverses the front and back of a sheet on which toner image formation is not completed on one side.

  The operation unit 90 is a user interface for operating the image forming apparatus 100. The operation unit 90 is configured by a touch screen, buttons, and switches in which a touch panel is superimposed on a liquid crystal panel.

  The paper feeding device 200 is a device that accommodates a larger amount of paper than the paper tray unit 30. In the case of outputting a large amount of sheets, the sheet feeder 200 is used instead of the sheet tray unit 30.

  The post-processing device 300 performs post-processing of the paper on which the image is formed. Specifically, the post-processing device 300 performs sort processing, punching (punching) processing, stapling processing, center folding processing, cutting processing, and the like.

  The printer controller 500 receives a print job from the user terminal 600 via a LAN (Local Area Network) 601. The printer controller 500 analyzes the print job, generates image data, and transmits the image data to the image forming apparatus 100 via the video bus 501.

  Here, the print job is data instructing printing of an image designated by the user terminal 600, and is described in, for example, a page description language (PDL) such as PostScript (registered trademark of Adobe) or PCL. Has been.

  Specifically, the printer controller 500 converts image data described in a page description language into data described in an intermediate language, and the first data having a predetermined first number of bits per pixel from the intermediate language data. Convert to drawing data. The printer controller 500 transmits the first drawing data as image data to the image forming apparatus 100 via the video bus 501. The predetermined first number of bits in the first drawing data is 8 bits in this example.

  The user terminal 600 is a terminal such as a personal computer. The user terminal 600 transmits a print job to the printer controller 500 via a LAN (Local Area Network) 601.

(Function of image forming apparatus)
Hereinafter, functions of the image forming apparatus according to the first embodiment will be described with reference to the drawings. FIG. 2 is a block diagram illustrating the image forming apparatus 100 according to the first embodiment.

  As shown in FIG. 2, the image forming apparatus 100 includes a control unit 400 that comprehensively controls the image forming apparatus 100. The control unit 400 includes a communication I / F 410, an HDD 420, a memory 430, and a CPU 440.

  The communication I / F 410 is connected to the video bus 501 and acquires the above-described first drawing data from the printer controller 500 as image data.

  The HDD 420 stores a control program, information regarding functions of the image forming apparatus 100, and the like.

  The memory 430 is configured by a semiconductor memory such as a DRAM. A control program stored in the HDD 420 is expanded on the memory 430. The memory 430 temporarily stores image data acquired by the image reading unit 20 and image data acquired by the communication I / F 410. Here, the memory 430 stores second drawing data described later as image data.

  The CPU 440 controls each component of the image forming apparatus 100 according to the control program developed on the memory 430. In the following, the operation of the CPU 440 related to the first embodiment will be mainly described. Therefore, it should be noted that a part of the operation of the CPU 440 is omitted.

  Specifically, CPU 440 compresses the first drawing data into second drawing data. The CPU 440 decompresses the second drawing data and generates decompressed drawing data. As illustrated in FIG. 3, the CPU 440 includes a calculation unit 441, a compression unit 442, a distribution unit 443, a shift unit 444, an expansion unit 445, a rasterization unit 446, and an instruction unit 447.

  In the first embodiment, when the first drawing data is compressed into the second drawing data, one set pixel (target set pixel) is configured by a plurality of adjacent pixels to be noted. In the second drawing data, the values of a plurality of adjacent pixels constituting the target set pixel constitute the value of one target set pixel. In the post-expansion drawing data, a plurality of adjacent pixels constituting the target set pixel have the same value.

  It should be noted that the first embodiment will be described on the assumption of the following contents. However, it is needless to say that the embodiment is not limited to such a premise.

(1) Pixel coordinate representation The coordinates of the pixel relating to the first drawing data are represented by f (x, y), the coordinates of the pixel relating to the second drawing data are represented by g (x, y), The coordinates of such a pixel are represented by h (x, y). An attention set pixel constituted by f (x, y) and f (x + 1, y) is represented by F (X, Y). An attention set pixel constituted by g (x, y) and g (x + 1, y) is represented by G (X, Y). An attention set pixel constituted by h (x, y) and h (x + 1, y) is represented by H (X, Y). Thus, in the first embodiment, the attention set pixel is configured by two pixels adjacent in the horizontal direction.

  Note that “x” and “X” represent horizontal coordinates, and “y” and “Y” represent vertical coordinates. Further, f (x, y), g (x, y), and h (x, y) have a one-to-one relationship. Further, in the X coordinate in the XY coordinate, one target set pixel corresponds to two pixels in the x coordinate in the xy coordinate. In the Y coordinate in the XY coordinate, one target set pixel corresponds to one pixel in the y coordinate in the xy coordinate.

(2) Bits Representing Pixels In the first drawing data, one pixel is represented by 8 bits. That is, in the first drawing data, one pixel has 256 gradations. In the second drawing data, one target pixel is represented by 2 bits. In the post-decompression drawing data, since a plurality of adjacent pixels constituting the target set pixel have the same value, one pixel has four gradations.

(3) Compression rate Since the target set pixel is composed of two adjacent pixels, the target set pixel is represented by 8 bits × 2 pixels = 16 bits in the first drawing data. In the second drawing data, the target set pixel is expressed by 2 bits. Therefore, the compression ratio for compressing the first drawing data into the second drawing data is 2/16 = 1/8.

  Returning to FIG. 3, the calculation unit 441 configures one target set pixel by a plurality of adjacent pixels to be noted (target adjacent pixels). Subsequently, the calculation unit 441 calculates the value of the target set pixel based on the value of the target adjacent pixel related to the first drawing data. In the first embodiment, the value of the target set pixel is an average value of the values of the target adjacent pixels related to the first drawing data.

  The compression unit 442 compares the value of the target set pixel related to the first drawing data with the determination threshold value, and encodes the value of the target set pixel related to the first draw data. In the post-decompression drawing data according to the first embodiment, since one pixel has four gradations, there are three types of determination threshold values: a first determination threshold value, a second determination threshold value, and a third determination threshold value. For example, the first determination threshold is “64”, the second determination threshold is “128”, and the third determination threshold is “196”.

  When the value of the target set pixel related to the first drawing data is less than the first determination threshold value, the compression unit 442 expresses the value of the target set pixel related to the second draw data as a bit string “00”. When the value of the target set pixel related to the first drawing data is equal to or greater than the first determination threshold and less than the second determination threshold, the compression unit 442 converts the value of the target set pixel related to the second drawing data to the bit string “10”. It expresses with. When the value of the target set pixel related to the first drawing data is greater than or equal to the second determination threshold and less than the third determination threshold, the compression unit 442 converts the value of the target set pixel related to the second drawing data to the bit string “01”. It expresses with. When the value of the target set pixel related to the first drawing data is greater than or equal to the third determination threshold, the compression unit 442 expresses the value of the target set pixel related to the second draw data as a bit string “11”.

  The compression unit 442 notifies the distribution unit 443 that the encoding of the value of the target set pixel related to the first drawing data has been completed.

  The distribution unit 443 distributes an error, which is a difference between the value of the target set pixel related to the first drawing data and the extension value of the target set pixel related to the second drawing data, to peripheral pixels provided around the target set pixel. Thus, the values of the peripheral pixels related to the first drawing data are corrected by the error.

  The decompression value is a value associated with the value of the target set pixel related to the second drawing data. Specifically, it is a value obtained by expanding the value of the target set pixel related to the second drawing data. In the post-expansion drawing data according to the first embodiment, since one pixel has four gradations, there are four types of expansion values: a first expansion value, a second expansion value, a third expansion value, and a fourth expansion value. . For example, the first decompression value corresponding to the bit string “00” is “0”, the second decompression value corresponding to the bit string “10” is “96”, and the third decompression value corresponding to the bit string “01” is The fourth decompression value corresponding to the bit string “11” is “255”.

  In the first embodiment, an error that is a difference between the value of F (X, Y) and the expansion value of G (X, Y) is represented by e (X, Y). Here, a case where e (X, Y) is distributed to F (X + 1, Y), F (X-1, Y + 1), F (X, Y + 1), and F (X + 1, Y + 1) will be described. Note that F (X + 1, Y) is an attention set pixel configured by f (x + 2, y) and f (x + 3, y). F (X-1, Y + 1) is an attention set pixel configured by f (x-2, y + 1) and f (x-1, y + 1). F (X, Y + 1) is an attention set pixel configured by f (x, y + 1) and f (x + 1, y + 1). F (X + 1, Y + 1) is an attention set pixel constituted by f (x + 2, y + 1) and f (x + 3, y + 1).

(1) (X + 1, Y), ie, f (x + 2, y) and f (x + 3, y) f (x + 2, y) = f (x + 2, y) + p ₁ × e (X, Y)
f (x + 3, y) = f (x + 3, y) + p ₂ × e (X, Y)

P ₁ and p ₂ are coefficients related to error distribution. In the first embodiment, p ₁ = p ₂ = 7/16. Note that p ₁ and p ₂ may be different values.

(2) (X−1, Y + 1), ie, f (x−2, y + 1) and f (x−1, y + 1) f (x−2, y + 1) = f (x−2, y + 1) + q ₁ × e (X, Y)
f (x-1, y + 1) = f (x-1, y + 1) + q ₂ × e (X, Y)
Note that q ₁ and q ₂ are coefficients related to error distribution. In the first embodiment, q ₁ = q ₂ = 3/16. Note that q ₁ and q ₂ may be different values.

(3) (X, Y + 1), that is, f (x, y + 1) and f (x + 1, y + 1) f (x, y + 1) = f (x, y + 1) + r ₁ × e (X, Y)
f (x + 1, y + 1) = f (x + 1, y + 1) + r ₂ × e (X, Y)
R ₁ and r ₂ are coefficients related to error distribution. In the first embodiment, r ₁ = r ₂ = 5/16. Note that r ₁ and r ₂ may be different values.

(4) (X + 1, Y + 1), ie, f (x + 2, y + 1) and f (x + 3, y + 1) f (x + 2, y + 1) = f (x + 2, y + 1) + s ₁ × e (X, Y)
f (x + 3, y + 1) = f (x + 3, y + 1) + s ₂ × e (X, Y)
Note that s ₁ and s ₂ are coefficients related to error distribution. In the first embodiment, s ₁ = s ₂ = 1/16. Note that s ₁ and s ₂ may be different values.

  The distribution unit 443 notifies the calculation unit 441 of the pixel value corrected by the error. In addition, the distribution unit 443 notifies the shift unit 444 that error distribution has been completed.

  The shift unit 444 repeats the shift of the target set pixel by shifting the target adjacent pixel until the compression of the first drawing data is finished. Specifically, the shift unit 444 shifts F (X, Y) by one attention set pixel in the horizontal direction or the vertical direction in the XY coordinates. That is, the shift unit 444 shifts f (x, y) by two pixels in the horizontal direction in the xy coordinates. The shift unit 444 shifts f (x, y) by one pixel in the vertical direction in the xy coordinates.

  The calculation unit 441, the compression unit 442, and the distribution unit 443 repeat processing for each shift of the target set pixel. Thereby, the compression unit 442 compresses the first drawing data into the second drawing data.

  In the first embodiment, the compression unit 442 converts the bit string corresponding to the values of the four target set pixels into values expressed in decimal numbers, and then sequentially converts the values expressed in decimal numbers as second rendering data. Store in the memory 430. As described above, in the post-expansion drawing data, since the two target adjacent pixels constituting the target set pixel have the same value, it should be noted that the value expressed in decimal is equivalent to the value of eight pixels. Should.

  The decompression unit 445 obtains the value of each pixel after decompressing the second rendering data into decompressed rendering data. Specifically, the decompression unit 445 reads a value stored in the memory 430, that is, a value expressed in decimal notation from the memory 430, and converts a value expressed in decimal notation into a bit string expressed in binary notation. Convert.

  Subsequently, the decompression unit 445 decompresses the bit string expressed in binary number for each target set pixel, and acquires the stretch value of the target set pixel related to the second drawing data. The decompression unit 445 sets the decompressed value of the target set pixel related to the second drawing data as the value of each target adjacent pixel constituting the target set pixel related to the post-expanded drawing data.

  For example, the decompression unit 445 decompresses the bit string “00” corresponding to the target set pixel related to the second drawing data, and acquires the first extension value “0” as the extension value of the target set pixel related to the second drawing data. To do. The decompression unit 445 sets “0” as the value of each pixel constituting the target set pixel related to the decompressed drawing data.

  The decompression unit 445 decompresses the bit string “10” corresponding to the target set pixel related to the second drawing data, and acquires the second extension value “96” as the extension value of the target set pixel related to the second drawing data. The decompression unit 445 sets “96” as the value of each pixel constituting the target set pixel related to the decompressed drawing data.

  The decompression unit 445 decompresses the bit string “01” corresponding to the target set pixel related to the second drawing data, and acquires the third extension value “160” as the extension value of the target set pixel related to the second drawing data. The decompression unit 445 sets “160” as the value of each pixel constituting the target set pixel related to the decompressed drawing data.

  The decompression unit 445 decompresses the bit string “11” corresponding to the target set pixel related to the second drawing data, and acquires the fourth extension value “255” as the extension value of the target set pixel related to the second drawing data. The decompression unit 445 sets “255” as the value of each pixel constituting the target set pixel related to the decompressed drawing data.

  The rasterizing unit 446 rasterizes the value of each pixel related to the decompressed drawing data. Specifically, the rasterizing unit 446 arranges the values of the pixels related to the decompressed drawing data in the xy coordinates, and acquires an array of pixel values.

  The instruction unit 447 instructs the image forming unit 50 to form an image. Specifically, the instruction unit 447 outputs the pixel value array acquired by the rasterizing unit 446 to the image forming unit 50. Specifically, the instruction unit 447 outputs an array of pixel values of colors corresponding to each write processing unit to each write processing unit provided in the image forming unit 50.

(Operation of image forming apparatus)
Hereinafter, the operation of the image forming apparatus according to the first embodiment will be described with reference to the drawings. FIG. 4 is a flowchart showing the operation of the image forming apparatus 100 according to the first embodiment. The flow shown in FIG. 4 is executed by the CPU 440 developing the program stored in the HDD 420 in the memory 430.

  As shown in FIG. 4, in step 100, the control unit 400 receives the first drawing data via the video bus 501.

  In step 200, the control unit 400 compresses the first drawing data into the second drawing data. Details of the compression process will be described later (see FIGS. 5 and 6).

  In step 300, the control unit 400 stores the second drawing data in the memory 430.

  In step 400, the control unit 400 decompresses the second drawing data read from the memory 430. Details of the decompression process will be described later (see FIGS. 7 and 8).

  In step 500, the control unit 400 rasterizes the value decompressed in step 400 to obtain an array of pixels constituting the image.

  In step 600, the control unit 400 instructs the image forming unit 50 to form an image.

  Details of the above-described compression processing will be described below with reference to FIGS.

  As shown in FIG. 5, in step 210a, the control unit 400 sets the Y coordinates of F (X, Y) and G (X, Y) in the XY coordinates. Note that the control unit 400 shifts the Y coordinate by one target set pixel in the XY coordinates when the loop processing from Step 210a to Step 210b is completed. Note that the loop processing from step 210a to step 210b is repeated until the compression processing is completed for all the pixels in the vertical direction.

  In addition, it should be noted that in step 210a, the control unit 400 sets the y coordinate of f (x, y) or g (x, y) in the xy coordinate. Note that the control unit 400 shifts the y coordinate by one pixel in the xy coordinates when the loop processing from step 210a to step 210b is completed.

  In step 220a, the control unit 400 sets the X coordinate of F (X, Y) or G (X, Y) in the XY coordinate. The control unit 400 shifts the X coordinates of F (X, Y) and G (X, Y) by one target set pixel in the XY coordinates when the loop processing from Step 220a to Step 220b is completed. Note that the loop processing from step 220a to step 220b is repeated until the compression processing is completed for all pixels in the horizontal direction.

  In addition, it should be noted that in step 220a, the control unit 400 sets the x coordinate of f (x, y) or g (x, y) in the xy coordinate. Note that the control unit 400 shifts the x coordinate by two pixels in the xy coordinates when the loop processing from step 220a to step 220b is completed.

  In step 230, the control unit 400 calculates the average value a of the values of f (x, y) and f (x + 1, y) constituting F (X, Y), that is, the value of F (X, Y). To do.

  For example, as shown in FIG. 6, the control unit 400 calculates an average value a “150” of the values of f (0, 0) and f (1, 0) constituting F (0, 0).

  In step 241, the control unit 400 determines whether or not the average value a is less than “64”. If the average value a is less than “64”, the control unit 400 proceeds to the process of step 251. If the average value “a” is equal to or greater than “64”, the control unit 400 proceeds to step 242.

  In step 242, the control unit 400 determines whether or not the average value a is “64” or more and less than “128”. When the average value “a” is “64” or more and less than “128”, the control unit 400 proceeds to step 253. If the average value “a” is equal to or greater than “128”, the control unit 400 proceeds to step 243.

  In step 243, the control unit 400 determines whether or not the average value “a” is “128” or more and less than “196”. When the average value a is “128” or more and less than “196”, the control unit 400 proceeds to the process of step 255. When the average value a is “196” or more, the control unit 400 proceeds to the process of step 257.

  In step 251, the control unit 400 sets “0” to g (x, y) and sets “0” to g (x + 1, y). That is, the control unit 400 expresses the value of G (X, Y) related to the second drawing data as a bit string “00”.

  In step 252, the control unit 400 sets the difference between the average value “a” and the first extension value “0” to e (X, Y).

  In step 253, the control unit 400 sets “1” to g (x, y) and sets “0” to g (x + 1, y). That is, the control unit 400 expresses the value of G (X, Y) related to the second drawing data by the bit string “10”.

  In step 254, the control unit 400 sets the difference between the average value “a” and the second extension value “96” to e (X, Y).

  In step 255, the control unit 400 sets “0” to g (x, y) and “1” to g (x + 1, y). That is, the control unit 400 expresses the value of G (X, Y) related to the second drawing data by the bit string “01”.

  In step 256, the control unit 400 sets the difference between the average value a and the third expansion value “160” to e (X, Y).

  In step 257, the control unit 400 sets “1” to g (x, y) and sets “1” to g (x + 1, y). That is, the control unit 400 expresses the value of G (X, Y) related to the second drawing data by the bit string “11”.

  In step 258, the control unit 400 sets the difference between the average value a and the fourth extension value “255” to e (X, Y).

  For example, as shown in FIG. 6, the control unit 400 expresses the value of G (0, 0) as a bit string “01” because the average value “150” is “128” or more and less than “196”. Further, the control unit 400 sets a difference “−10” between the average value “a” “150” and the third extension value “160” to e (0, 0).

  In step 260, the control unit 400 determines that F (X + 1, Y), F (X-1, Y + 1), F (X, Y + 1), F (X + 1, Y + 1) provided around F (X, Y). Distribute e (X, Y). Note that F (X + 1, Y) is an attention set pixel configured by f (x + 2, y) and f (x + 3, y). F (X-1, Y + 1) is an attention set pixel configured by f (x-2, y + 1) and f (x-1, y + 1). F (X, Y + 1) is an attention set pixel configured by f (x, y + 1) and f (x + 1, y + 1). F (X + 1, Y + 1) is an attention set pixel constituted by f (x + 2, y + 1) and f (x + 3, y + 1).

As described above, the distribution of e (X, Y) is performed as follows.
(1) (X + 1, Y), ie, f (x + 2, y) and f (x + 3, y) f (x + 2, y) = f (x + 2, y) + p ₁ × e (X, Y)
f (x + 3, y) = f (x + 3, y) + p ₂ × e (X, Y)
(2) (X−1, Y + 1), ie, f (x−2, y + 1) and f (x−1, y + 1) f (x−2, y + 1) = f (x−2, y + 1) + q ₁ × e (X, Y)
f (x-1, y + 1) = f (x-1, y + 1) + q ₂ × e (X, Y)
(3) (X, Y + 1), ie, f (x, y + 1) and f (x + 1, y + 1) f (x, y + 1) = f (x, y + 1) + r ₁ × e (X, Y)
f (x + 1, y + 1) = f (x + 1, y + 1) + r ₂ × e (X, Y)
(4) (X + 1, Y + 1), ie, f (x + 2, y + 1) and f (x + 3, y + 1) f (x + 2, y + 1) = f (x + 2, y + 1) + s ₁ × e (X, Y)
f (x + 3, y + 1) = f (x + 3, y + 1) + s ₂ × e (X, Y)

For example, as shown in FIG. 6, the control unit 400 corrects the values of the surrounding pixels as follows. Since the pixel value does not take a negative value, the minimum value of the pixel value is “0”.
f (2,0) = 100 + 7/16 × −10≈96
f (3,0) = 0 + 7/16 × −10≈0
f (0,1) = 100 + 5/16 × −10≈97
f (1,1) = 50 + 5/16 × −10≈47
f (2,1) = 200 + 1/16 × −10≈200
f (3,1) = 200 + 1/16 × −10≈200

In this manner, the control unit 400 compresses the first drawing data into the second drawing data for all the pixels by repeating the loop processing of Step 210a to Step 210b.

  In step 270, the control unit 400 converts the bit string corresponding to the four G (X, Y) into a value expressed in decimal.

  For example, as shown in FIG. 6, the control unit 400 converts the bit string “01001011” into a value “75” expressed in decimal.

  Details of the above-described decompression processing will be described below with reference to FIGS.

  As shown in FIG. 7, in step 410a, the control unit 400 sets the Y coordinate of G (X, Y) or H (X, Y) in the XY coordinates. Note that the control unit 400 shifts the Y coordinate by one target set pixel in the XY coordinates when the loop processing from Step 410a to Step 410b is completed. Note that the loop processing from Step 410a to Step 410b is repeated until the expansion processing is completed for all the pixels in the vertical direction.

  In addition, it should be noted that in step 410a, the control unit 400 sets the y coordinate of g (x, y) or h (x, y) in the xy coordinate. Note that the control unit 400 shifts the y coordinate by one pixel in the xy coordinates when the loop processing from step 410a to step 410b is completed.

  In step 420a, the control unit 400 sets the X coordinates of G (X, Y) and H (X, Y) in the XY coordinates. Note that the control unit 400 shifts the X coordinates of G (X, Y) and H (X, Y) by four attention set pixels in the XY coordinates when the loop processing of Step 420a to Step 420b is completed. The reason for shifting by four attention set pixels is that the second drawing data corresponding to the four attention set pixels is expressed in decimal numbers, and the second drawing data expressed in decimal numbers is stored in the memory 430. . Note that the loop processing from step 420a to step 420b is repeated until the expansion processing is completed for all pixels in the horizontal direction.

  In addition, it should be noted that in step 420a, the control unit 400 sets the x coordinate of g (x, y) or h (x, y) in the xy coordinate. Note that the control unit 400 shifts the x coordinate by 8 pixels in the xy coordinates when the loop process of step 420a to step 420b is completed.

  In step 430, the control unit 400 converts the value stored in the memory 430, that is, the value expressed in decimal numbers into a bit string expressed in binary numbers.

  For example, as shown in FIG. 8, the control unit 400 converts a value “75” expressed in decimal numbers into a bit string “01001011”.

  It should be noted that in step 440a, the control unit 400 sets the x coordinate of g (x, y) or h (x, y) in the xy coordinate. Note that the control unit 400 shifts the x coordinate by two pixels in the xy coordinates when the loop processing from step 440a to step 440b is completed. The loop processing from step 440a to step 440b is repeated the number of times corresponding to four attention set pixels, that is, four times.

  In step 451, the control unit 400 determines whether g (x, y) = 0 and g (x + 1, y) = 0. That is, the control unit 400 determines whether or not the bit string corresponding to G (X, Y) is “00”. If the bit string corresponding to G (X, Y) is “00”, the control unit 400 proceeds to the process of step 461. If the bit string corresponding to G (X, Y) is not “00”, the control unit 400 proceeds to the process of step 452.

  In step 452, the control unit 400 determines whether g (x, y) = 1 and g (x + 1, y) = 0. That is, the control unit 400 determines whether or not the bit string corresponding to G (X, Y) is “10”. If the bit string corresponding to G (X, Y) is “10”, the control unit 400 proceeds to the process of step 462. If the bit string corresponding to G (X, Y) is not “10”, the control unit 400 proceeds to the process of step 453.

  In step 453, the control unit 400 determines whether g (x, y) = 0 and g (x + 1, y) = 1. That is, the control unit 400 determines whether or not the bit string corresponding to G (X, Y) is “01”. If the bit string corresponding to G (X, Y) is “01”, the control unit 400 proceeds to the process of step 463. If the bit string corresponding to G (X, Y) is “11”, the control unit 400 proceeds to the process of step 464.

  In step 461, the control unit 400 sets “0” as the value of h (x, y) and sets “0” as the value of h (x + 1, y).

  In step 462, the control unit 400 sets “96” as the value of h (x, y) and sets “96” as the value of h (x + 1, y).

  In step 463, the control unit 400 sets “160” as the value of h (x, y) and sets “160” as the value of h (x + 1, y).

  In step 464, the control unit 400 sets “255” as the value of h (x, y) and sets “255” as the value of h (x + 1, y).

  For example, as shown in FIG. 8, the control unit 400, when the bit string corresponding to G (0,0) is “01”, that is, g (0,0) = 0 and g (1,0) ) = 1, “160” is set as the value of h (0,0) and h (1,0). Further, the control unit 400 determines that the bit string corresponding to G (1, 0) is “00”, that is, when g (2, 0) = 0 and g (3, 0) = 0. Sets “0” as the value of h (2,0) and h (3,0).

(Comparison result)
Hereinafter, a comparison result of the original image, the image after the error diffusion method of the prior art, and the image after the error diffusion method of the embodiment will be described with reference to FIG. FIG. 9A is an enlarged view of the original image and a part thereof. FIG. 9B is an enlarged view of an image after a conventional error diffusion method and a part thereof. FIG. 9C is an enlarged view of an image after the error diffusion method of the embodiment and a part thereof.

  From a comparison between FIG. 9A and FIG. 9B, it can be seen that the image after the error diffusion method of the prior art has a lower resolution than the original image.

  From the comparison between FIG. 9B and FIG. 9C, it is found that the resolution reduction is suppressed in the image after the error diffusion method of the embodiment compared to the image after the error diffusion method of the prior art. I understand. That is, it can be seen from the comparison between FIG. 9A and FIG. 9C that the image after the error diffusion method of the embodiment is closer to the original image than the image after the error diffusion method of the prior art.

(Function and effect)
The control unit 400 configures one target set pixel by a plurality of target adjacent pixels, and encodes the value of the target set pixel related to the first drawing data. In other words, the control unit 400 compresses the first drawing data into the second drawing data for each set pixel of interest.

  Accordingly, the value of the target set pixel related to the second drawing data can be expressed by the number of bits assigned to the plurality of target adjacent pixels constituting the target set pixel. That is, by increasing the number of bits representing the value of the target collection pixel related to the second drawing data, it is possible to increase the number of gradations of the pixel related to the decompressed drawing data.

  As described above, in the case of using the error diffusion method, the number of gradations of the pixels can be increased without reducing the compression rate, so that deterioration of the quality of the image formed on the paper can be suppressed. Of course, it is not necessary to reduce the resolution.

[Other Embodiments]
Although the present invention has been described with reference to the above-described embodiments, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, the image forming apparatus 100 may not be an MFP but may be an apparatus having only a printer function or an apparatus having only a copying function.

  In the embodiment described above, the value of the target set pixel related to the second drawing data is expressed by 2 bits, but the embodiment is not limited to this. The value of the target set pixel related to the second drawing data may be expressed by 4 bits or may be expressed by 8 bits. As described above, if the number of bits representing the value of the target set pixel related to the second drawing data is increased, the number of gradations of the pixel related to the post-decompression drawing data increases.

  For example, when the value of the target set pixel related to the second drawing data is expressed by 4 bits, one pixel in the decompressed drawing data has 16 gradations, and the compression rate is 4/16 = 1/4. is there. When the value of the target set pixel related to the second drawing data is expressed by 8 bits, one pixel in the decompressed drawing data has 256 gradations, and the compression rate is 8/16 = 1/2.

  In the embodiment described above, the attention set pixel is configured by two pixels adjacent in the horizontal direction, but the embodiment is not limited to this. The target set pixel may be configured by two pixels adjacent in the vertical direction.

  In the embodiment described above, the number of pixels constituting the target set pixel is “2”, but the embodiment is not limited to this. The number of pixels constituting the target set pixel may be “4” or “8”. As described above, if the number of pixels constituting the target set pixel is increased, the compression rate is increased.

  For example, if the number of bits representing the value of the target set pixel related to the second drawing data is “2”, the compression rate is 2/32 when the number of pixels constituting the target set pixel is “4”. = 1/16. Similarly, when the number of pixels constituting the target set pixel is “8”, the compression ratio is 2/64 = 1/32.

  The number of pixels constituting the target set pixel may be determined by a compression rate for compressing the first drawing data into the second drawing data and the number of gradations of the pixels related to the decompressed drawing data. For example, in a case where a high compression rate and a large number of gradations are required, the number of pixels constituting the target set pixel may be increased.

  In the embodiment described above, the compression process of the first drawing data is performed by the image forming apparatus 100, but the embodiment is not limited to this. The first drawing data compression process may be performed by the printer controller 500.

  Although not specifically mentioned in the above-described embodiment, a program for causing a computer to execute compression processing of the first data may be provided.

  In the above-described embodiment, the conversion process from the PDL to the intermediate language is performed by the printer controller 500, but the embodiment is not limited to this. The conversion process from the PDL to the intermediate language may be performed by the user terminal 600.

1 is a diagram illustrating an outline of an image forming apparatus 100 according to a first embodiment. It is a figure which shows the structure of the control unit 400 which concerns on 1st Embodiment. It is a figure which shows the structure of CPU440 which concerns on 1st Embodiment. FIG. 5 is a flowchart showing an operation of the image forming apparatus 100 according to the first embodiment. FIG. 5 is a flowchart showing an operation of the image forming apparatus 100 according to the first embodiment. It is a figure for demonstrating the compression process which concerns on 1st Embodiment. FIG. 5 is a flowchart showing an operation of the image forming apparatus 100 according to the first embodiment. It is a figure for demonstrating the expansion | extension process which concerns on 1st Embodiment. It is a figure which shows the comparison result of a prior art and embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Automatic document feeding unit, 20 ... Image reading unit, 30 ... Paper tray unit, 40 ... Paper feed unit, 50 ... Image forming unit, 60 ... Fixing unit, 70 ..Paper discharge unit, 80... Reversing unit, 90... Operation unit, 100... Image forming apparatus, 200. , 410 ... Communication I / F, 420 ... HDD, 430 ... Memory, 440 ... CPU, 441 ... Calculation part, 442 ... Compression part, 443 ... Distribution part, 444 ... Shift unit, 445 ... Extension unit, 446 ... Rasterize unit, 447 ... Instruction unit

Claims (4)

An image forming apparatus for forming an image on paper,
A controller that compresses the first drawing data into second drawing data, decompresses the second drawing data, and obtains drawing data after decompression;
An image forming unit that forms an image on a sheet based on the decompressed drawing data in accordance with an instruction from the control unit;
The controller is
A target set pixel is configured by a plurality of adjacent pixels to be noted, and the target set related to the first drawing data is based on values of the plurality of adjacent pixels related to the set target pixel of the first drawing data A calculation unit for calculating a pixel value;
A compression unit that compares the value of the target set pixel related to the first drawing data with a determination threshold and encodes the value of the target set pixel related to the first drawing data;
An error, which is a difference between the value of the target set pixel related to the first drawing data and the extension value of the target set pixel related to the second drawing data, is distributed to peripheral pixels provided around the target set pixel A distribution unit that corrects a value of the peripheral pixel related to the first drawing data by the error;
A shift unit that repeats the shift of the target set pixel by shifting the plurality of adjacent pixels of interest until the compression of the first drawing data is finished,
The image forming apparatus, wherein the calculation unit, the compression unit, and the distribution unit repeat the process for each shift of the plurality of pixels of interest.   2. The calculation unit according to claim 1, wherein the calculation unit calculates an average value of the values of the plurality of adjacent pixels related to the first drawing data as a value of the target set pixel related to the first drawing data. Image forming apparatus.   The number of the plurality of adjacent pixels constituting the target set pixel is determined by a compression rate for compressing the first drawing data into the second drawing data and a gradation number of one pixel related to the decompressed drawing data. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A data compression method for compressing first drawing data into second drawing data,
A target set pixel is constituted by a plurality of adjacent pixels to be noted, and the value of the target set pixel related to the first drawing data is determined based on the values of the plurality of adjacent pixels related to the first drawing data. Calculating step A;
Comparing the value of the target set pixel related to the first drawing data with a determination threshold, and encoding the value of the target set pixel;
An error, which is a difference between the value of the target set pixel related to the first drawing data and the expanded value of the target set pixel related to the second drawing data, is distributed to peripheral pixels provided around the target set pixel. A step C of correcting the value of the surrounding pixels related to the first drawing data by the error;
Repetitively shifting the target set pixel by shifting the plurality of pixels of interest until the compression of the first drawing data is completed,
Step A, Step B, and Step C are repeated for each shift of the plurality of adjacent pixels to be noted.