JP5586652B2 - Image processing apparatus and automatic gradation correction method - Google Patents

Description

  Embodiments described herein relate generally to an image processing apparatus and an automatic gradation correction method.

  In an image processing apparatus (multifunctional peripheral, MFP), the gradation (image density) of print output (output image) is automatically set based on conditions such as the total number of prints, temperature, humidity, and fixing device temperature. Correction (automatic gradation correction) is performed to stabilize printing reproduction (gradation of output image).

JP 2005-1007047 A

  In automatic gradation correction to stabilize print reproduction (gradation of output image), color images can be printed on an image carrier such as an intermediate transfer belt or a photosensitive drum in order to improve gradation correction performance. A test pattern for each color (for CMYK) is printed, and the density of the test pattern is read to determine a correction amount used for tone correction. The test pattern for each color includes, for example, 10 or more gradation patches.

  That is, by printing a large number (more than a predetermined number) of CMYK tone patches on the image carrier, the size of the test pattern (printing area) for each color is increased. Further, it is necessary to repeat the test pattern printing for each color for each color.

  This requires a lot of time until the end of the automatic gradation correction that enables printing.

  An object of the present invention is to reduce the time required for automatic gradation correction of an image processing apparatus.

In the embodiment, the image processing apparatus includes a detecting unit, an image generating unit, and an image forming unit. The detection means obtains the density of each patch of the first density pattern image formed of M (M is a positive integer) patches having different tone values in the first color held by the image carrier. Image generating means, a second density pattern image comprising a plurality of patches having different gradation values different from the second color to the first color, said detection means before Symbol first density pattern image As a result of obtaining the density of each patch, the number of patches is reduced to N (N ≦ M) by thinning out a gradation value area where there is no significant difference in density difference or a gradation value area where the density value is regarded as a straight line. , N is a positive integer) and the generation of the second density pattern image is instructed. The image forming unit forms the second density pattern image instructed by the image generating unit on the image carrier. The first density pattern image is formed with black toner.

Schematic which shows an example of the image processing apparatus to which the embodiment is applied. Schematic which shows an example of the image process part of the image processing apparatus to which embodiment is applied. 1 is a schematic diagram illustrating an example of an image forming unit of an image processing apparatus to which an embodiment is applied. Schematic which shows an example of the test pattern which the image processing apparatus to which the embodiment is applied uses. Schematic which shows an example of the relationship between the gradation value of a test pattern and the sensor output which the image processing apparatus to which the embodiment is applied. Schematic which shows an example of the gradation correction process of the image processing apparatus to which the embodiment is applied. Schematic which shows an example of the sensor output and the gradation value of N patterns which the image processing apparatus to which the embodiment is applied. Schematic which shows an example of the image processing apparatus to which the embodiment is applied. Schematic which shows an example of the image processing apparatus to which the embodiment is applied.

  Hereinafter, embodiments will be described with reference to the drawings.

  An image processing apparatus 1 (multi-function peripherals, hereinafter simply referred to as MFP) 1 shown in FIG. 1 includes an image reading unit 11, an image processing unit 21, an image forming unit 31, an operation unit 41, and main control. Section (Main Processing Unit, hereinafter simply referred to as MPU) 51. Each of the image reading unit 11, the image processing unit 21, and the image forming unit 31 has a control unit (CPU) that controls the operation of each unit in accordance with an instruction from the MPU 51. A part of the CPU that controls the operation of each unit may be shared.

  The image reading unit 11 includes a reading device (photoelectric conversion device) such as a CCD sensor, and outputs image data corresponding to a document image. The reading device reads a document image and converts it into image data. In other words, the reading device acquires character and image information of the reading object as light brightness and darkness, and generates image data corresponding to light and darkness.

  The image processing unit 21 performs image processing such as color conversion, image area identification, input image quality enhancement processing, compression / expansion processing, gradation correction, and halftone processing on the image data output from the image reading unit. The image processing unit 21 is also connected to an external input interface (image input unit) 51 and receives image data supplied from an external device such as a PC (Personal Computer).

  The image forming unit 31 forms an image on a sheet based on the image data output from the image processing unit 21 (print output).

  The operation unit 41 is capable of inputting numerical values such as an operation input by the user and an automatic gradation correction to be described below and manual gradation value setting.

  An example of the configuration of the image processing unit 21 will be described with reference to FIG.

  The image processing unit 21 includes, for example, a color conversion unit 22, an image area identification unit 23, an input image quality enhancement processing unit 24, a compression / decompression processing unit 25, a gradation correction unit 26, a halftone processing unit 27, and a patch (test pattern). The generation processing unit 28 and the like are included. Further, it has a CPU (sub processor) 29 that controls the operation of each unit in accordance with an instruction from the MPU 51.

  The color conversion unit 22 converts the image data output from the image reading unit 11 (hereinafter referred to as input image data) from input RGB (R: red, G: green, B: blue) to CMYK for print output. (C or cyan, M or magenta, Y or yellow, K or black (black)) is converted into color material density data.

  The image area identification unit 23 divides the input image data into, for example, a character and a photograph area.

  When the input image data is a character, the input high image quality processing unit 24 specifies the contour and performs correction processing such as contour enhancement.

  The compression / decompression processing unit 25 compresses input image data for recording and storage in a storage device such as an HDD (hard disk device), and decompresses the input image data when output to the image forming unit 31.

  The gradation correction unit 26 matches the CMYK density characteristics used for printing with the gradation characteristics of the input image data.

  The halftone processing unit 27 performs halftone processing for improving the reproducibility of a photographic area or the like of the input image data.

  The patch generation processing unit 28 corrects the output characteristic (density characteristic) of the gradation correction unit 26 and the density of each patch of the test pattern (patch image) used for automatic adjustment (automatic gradation correction). Set. Note that the number of patch images (test patterns) is set according to an instruction value from the image forming unit 31 described in FIG.

  FIG. 3 illustrates an example of the configuration of the image forming unit 31.

  The image forming unit 31 includes, for example, first to fourth monochrome image forming stations 32a, 32b, 32c and 32d, an intermediate transfer member (intermediate transfer belt) 33, a sheet transfer unit 34, a sensor unit 35, a fixing unit 36, and a CPU. (Sub-processor) 37 is included.

  The first to fourth stations 32a, 32b, 32c, and 32d each form a visualized image (image) of each color of CMYK. Each station has, for example, an electro-optical conversion (exposure) unit such as a laser optical system, an image carrier (photosensitive drum), a developing unit, and a transfer unit. The exposure unit forms an electrostatic image (latent image) as an image pattern on the photosensitive drum with image light obtained by converting the image data output from the image processing unit 21 into light intensity. In the developing unit, the latent image is developed with a developer, that is, toner. The transfer unit moves the developed toner image to the intermediate transfer belt 33. The color of the image formed by each station is determined according to the characteristics of the toner, the order in which the images are superimposed, and the like.

  The intermediate transfer belt 33 conveys images formed by the stations 32a, 32b, 32c, and 32d.

  The sheet transfer unit 34 moves an image conveyed by the intermediate transfer belt 33, that is, a toner image, to a sheet, that is, a sheet.

  The sensor unit 35 detects the density of the image conveyed by the intermediate transfer belt 33, that is, the toner image on the intermediate transfer belt 33. The sensor unit 35 includes at least an optical density sensor (reflection density sensor) or an electrostatic density sensor (capacitance density sensor), for example.

  The fixing unit 36 integrates the image that the sheet transfer unit 34 moves to the sheet and the sheet.

  Note that the CPU (sub-processor) 37 controls the operation of each unit in accordance with an instruction from the MPU 51, and sends a characteristic value to the patch generation processing unit 28 (of the image processing unit 21) in accordance with the output (characteristic value) of the sensor unit 35. An instruction value corresponding to (output of the sensor unit 35) is output.

  Next, automatic gradation adjustment (gradation correction) will be described.

In the automatic gradation correction mode, on the intermediate transfer belt 33 shown in FIG. 3, M (M is a positive integer) the patch (test pattern) image of a first color developer, for example, black (hereinafter K (Color) and a color developer. Each patch has predetermined densities (tone values) a1, a2,..., A (M−1), aM (number of patches = M, M is a positive integer) as shown in FIG. Have. Note that the number M of patch images in the K color is preferably 10 or more, for example.

  The sensor unit 35 detects the density of each patch (the density of the toner developed by the developing unit of the latent image on the photosensitive drum and transferred to the intermediate transfer belt by the transfer unit). As a result, for example, the CPU 37 or its firmware obtains the correspondence between the gradation value (the gradation value of the patch image) and the sensor value (the detected density or characteristic value by the sensor unit 35) as shown in FIG. Note that, for example, a characteristic calculation unit for obtaining a correspondence relationship between the gradation value and the sensor value (characteristic value) may be provided independently.

  Incidentally, in the sensor value (characteristic value) shown in FIG. 5, there is no significant difference in the corresponding sensor value (characteristic value) between a2 and a3 in the low gradation region where the gradation value is low. In this case, even if the patch of the gradation value a2 is not printed, the gradation value a2 is obtained by the interpolation calculation based on the two sensor values (characteristic values) corresponding to the patch of the gradation value a1 and the patch of the gradation value a3. The sensor value (characteristic value) corresponding to can be obtained with high accuracy. That is, the characteristic value can be easily obtained by the CPU 37 or its firmware or characteristic calculation unit.

  When this phenomenon occurs, it can be presumed that no significant difference appears in the sensor value in the low gradation region in the CMY color different from the K color. For this reason, the sensor values can be obtained with high accuracy even for CMY colors without preparing patches in a specific low gradation range. That is, if the correlation between the K color and the CMY color is used, the number of patch images of the CMY colors is determined by a predetermined number N (N is a positive integer, N ≦ M) can be reduced.

  Therefore, for CMY colors, the number of patch images is N (N ≦ M), the distance from the front end to the end of the patch (on the intermediate transfer belt 33), and the corresponding image formation and sensor unit 35. The time required for detecting the characteristic value is reduced. Therefore, the time required for automatic gradation correction can be reduced.

  FIG. 6 is a flowchart showing a method for reducing the number of patch images for obtaining the sensor values (characteristic values) shown in FIGS. 4 and 5 for the CMY colors.

  First, a black (K) color test pattern (patch image) is printed [ACT1]. Subsequently, the density (characteristic value) of each patch image of the black (K) test pattern is detected by a sensor [ACT2]. That is, in [ACT1] and [ACT2], a black test pattern image is printed, and the characteristic value of each patch on the test pattern is read.

  Next, the correspondence between the gradation value of the black (K) color test pattern and the sensor value (characteristic value) is calculated [ACT3]. That is, the correspondence (correspondence data) between the gradation value and the sensor value (characteristic value) described with reference to FIG. 5 is obtained.

  Next, the gradation value of each patch (image) of the test pattern is calculated for other colors (CMY colors) [ACT4]. That is, based on the correspondence data obtained in [ACT3], the gradation value in each patch of the test pattern of other (CMY) colors is calculated. At this time, the number of gradation values, that is, the number N of patch images is in the range of N ≦ M.

  Next, a test pattern (patch image) is printed for any one of the other colors (CMY colors) [ACT5]. Subsequently, the density (characteristic value) of each patch image of the test pattern is detected by a sensor [ACT6]. That is, in [ACT5] and [ACT6], a test pattern (patch image) is printed for any one of CMY colors, and the characteristic value of each patch is read.

  Hereinafter, printing of the test pattern [ACT5] and reading of the characteristic value of the patch image by the sensor [ACT6] for all the colors (CMY) other than the K (black) color, the remaining two colors of the CMY colors Repeat for [ACT7].

  Next, the gradation correction amount for each color of CMYK is calculated [ACT8]. That is, the gradation correction amount of each CMYK color is calculated based on the acquired patch reading characteristic value of each CMYK color.

  For patch images in CMY colors, regardless of the low gradation range shown in FIG. 5, for example, a (Mu), a (Mv), a (Mw) shown in FIG. For example, a (M−v) can be omitted for gradation values that are sensor values that can be regarded as a substantially straight line.

  In this case, the gradation values of the three patches a (M−u), a (M−v), and a (M−w) are expressed as a (M−u) and a (M−v). The number of patches may be reduced by setting a (M-uv) between them, and a (M-vw) between a (Mv) and a (Mw).

  That is, it is possible to simply thin out the patch images and interpolate the characteristic values, and it is also possible to obtain characteristic values corresponding to new gradation values based on the characteristic values of the two patch images.

  FIG. 8 shows another embodiment of the image processing apparatus shown in FIG.

  A recording apparatus (MFP) 101 using an ink jet method shown in FIG. 8 includes a housing 102, a paper cassette 103, an image forming unit 104, a paper discharge tray 105, and a first transport path A1 from the paper cassette 103 to the image forming unit 104. And a transport device 106 that transports the paper along the second transport path A2 from the image forming unit 104 to the paper discharge tray 105, a reversing device 107 that reverses the front and back of the paper, a control device (CPU) 111, and the like. .

  The image forming unit 104 holds the paper on the outer peripheral surface, moves the first surface (recording surface) of the paper at a predetermined speed, a fixing device 141 that fixes the paper to the outer peripheral surface of the drum 140, and the drum 140. The first to fourth recording heads 143 a, 143 b, 143 c, and 143 d that provide ink to the paper held by the outer peripheral surface of the paper and form an image on the paper, and the static elimination device 144 and the drum 140 that peel the paper from the drum 140 A cleaning device 145 for cleaning and a sensor unit 135 for detecting the density of the image on the paper are provided. The sensor unit 135 includes at least an optical density sensor (reflection density sensor), for example.

  The recording heads 143a, 143b, 143c, and 143d each form a visualized image (image) or a test pattern (patch) image of each color of CMYK. The color of the image formed by each recording head is determined according to the characteristics of the ink, the order in which the images are superimposed, and the like. Further, the density of the image formed by each recording head 143a, 143b, 143c, and 143d detected by the sensor unit 135 is determined as a density value (characteristic value) in a gradation determination in a CPU (Central Processing Unit). Use.

  Hereinafter, automatic density correction is executed according to the embodiment shown in FIGS.

  FIG. 9 shows another embodiment of the image processing apparatus shown in FIG.

  9 includes a paper cassette 202, a paper feed roller 203, a paper feed path 204, a registration roller 205, a suction roller 206, a transport device 207, a recording / erasing device 208, a paper discharge path 209, A density sensor (sensor unit) 235, a control device (CPU) 210, discharge rollers 211 (plural), a discharge tray 212, and the like are provided. The sensor unit 235 includes at least an optical density sensor (reflection density sensor), for example.

  The sheet conveyed from the sheet feeding cassette 202 by the sheet feeding roller 203 passes through the sheet feeding path 204 and the registration roller 205 and is fixed to the conveying belt 273 of the conveying device 207 by electrostatic force from the suction roller 206.

  The suction roller 206 presses the sheet supplied by the registration roller 205 against the conveyance belt 273 and fixes the sheet (the sheet) to the outer peripheral surface of the conveyance belt 273. As the driving roller 271 rotates, the sheet adsorbed on the outer peripheral surface of the conveyor belt 273 moves in the direction indicated by the arrow.

  When an image is formed on the sheet conveyed by the conveyance belt 207, the recording / erasing device 208 erases the formed image, and forms a new image after erasing. The recording / erasing device 208 includes first to fourth recording heads 208a, 208b, 208c, and 208d, and uses C (cyan), M (magenta), Y (yellow), and K (black) inks. Form an image.

  The paper on which the recording / erasing device 208 has formed an image passes through the paper discharge path 209 and moves to the paper discharge tray 212 via the discharge roller 211.

  Each of the recording heads 208a, 208b, 208c, and 208d forms a visualized image (image) or a test pattern (patch) image of each color of CMYK. The color of the image formed by each recording head is determined according to the characteristics of the ink, the order in which the images are superimposed, and the like. Further, the density of an image formed by each recording head 208a, 208b, 208c, 208d detected by the sensor 235 is used as a density value (characteristic value) for gradation determination in a CPU (Central Processing Unit) 210. .

  Hereinafter, automatic density correction is executed according to the embodiment shown in FIGS.

  An example of an embodiment of ink suitable for use by each recording head 208a, 208b, 208c, 208d is shown.

  In the present embodiment, an ink having a characteristic of decoloring (discoloring) when heat equal to or higher than a predetermined erasing temperature is applied is used.

  As such an ink, for example, an ink containing a color developing compound, a developer, a binder resin, and the like as components can be used. In such an ink, since the color developing compound is colored in advance by the action of the developer, the user can recognize the color. Applying heat above the erasing temperature to the colored ink softens the binder resin, making it easier for the developer to move from the inside of the binder resin to the surface, and in the direction of the thickness of the paper that is the recording medium. It becomes easier to move inward or diffuse. For this reason, the color developable compound is not affected by the developer, and the color developable compound is decolored so that the color of the ink cannot be recognized.

  Color developing compounds are precursor compounds of dyes that form color images such as letters and figures, and are leucooramines, diarylfurides, polyarylcarbinols, acylauramines, allyololamines. It is preferable to use electron-donating organic substances such as rhodamine B lactams, indolines, spiropyrans, and fluorans.

  The color developer is a compound that develops a color of the color developing compound by interacting with the color developing compound (mainly exchange of electrons or putron), and phenols, phenol metal salts, carboxylic acid metal salts, benzophenones, sulfones. Preferably, sulfonic acid salts, phosphoric acids, phosphoric acid metal salts, acidic phosphoric acid esters, acidic phosphoric acid ester metal salts, phosphorous acids, phosphorous acid metal salts and the like are used.

  The binder resin disperses the color developable compound and the developer in a colored state. On the other hand, it has a characteristic that it is compatible with the color-forming compound during heating and has no affinity with the colorant.

  When ink containing such components is used, if heat above the erasing temperature is applied to the ink during printing, the ink before being ejected onto the paper or the ink after adhering to the paper is erased, resulting in normal image formation results May not be obtained. Accordingly, the first to fourth recording heads 208a, 208b, 208c, and 208d are preferably of a piezo type. Further, by providing a heat radiating plate on the first to fourth recording heads 208a, 208b, 208c, 208d, etc., it is possible to prevent the temperature of the ink stored in each of the 208a, 208b, 208c, 208d from rising undesirably. It is preferable.

  As described above, in any method, a characteristic value is obtained for a black (K) color by a test pattern including M patch images, and a test pattern including N (N ≦ M) patch images for CMY colors. Is used to reduce the distance from the front end to the end of the patch (on the intermediate transfer belt 33) and the time required for the corresponding image formation and detection of the characteristic value by the sensor unit 35. Therefore, the time required for automatic gradation correction can be reduced.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... MFP (image processing apparatus), 11 ... Image reading part, 21 ... Image processing part (image processing means), 22 ... Color conversion part, 23 ... Image area identification part, 24 ... Input image quality improvement processing part, 25 ... Compression / decompression processing unit, 26 ... gradation correction unit, 27 ... halftone processing unit, 28 ... patch (test pattern) generation processing unit (test pattern generation means), 29 ... CPU (sub-processor), 31 ... image forming unit 33 ... Intermediate transfer belt (image holding means), 35 ... sensor unit (density sensor), 37 ... CPU (sub processor), 41 ... operation unit, 51 ... MPU (main control unit), 101,201 ... MFP (recording) Devices), 111, 210... CPU (control device), 135, 235... Sensor unit (concentration sensor).

Claims (6)

Detection means for obtaining the density of each patch of the first density pattern image composed of M (M is a positive integer) patches having different tone values in the first color held by the image carrier;
The concentration of individual patches of the first different second as a second density pattern image comprising a plurality of patches of different gradation values in color, said detection means before Symbol first density pattern image from the color As a result, the number of patches is reduced to N (N ≦ M, where N is a positive value) by thinning out a gradation value area where there is no significant difference in density difference or a gradation value area where the density value is regarded as a straight line. An image generation means for instructing generation of a second density pattern image that is an integer) ,
Image forming means for forming the second density pattern image instructed by the image generating means on the image carrier ,
The first density pattern image is an image processing apparatus formed with black toner . The image processing apparatus according to claim 1, wherein the image generation unit interpolates density values between patches of the first density pattern image based on density values of individual patches of the first density pattern image. The image processing apparatus according to claim 1, wherein the image forming unit includes a unit that forms the first density pattern image on the image carrier . Forming a first density pattern image composed of M patches (M is a positive integer) with different gradation values in the first color on the image carrier;
Determine the density of each patch of the first density pattern image formed on the image carrier,
As a second density pattern image composed of a plurality of patches with different tone values in a second color different from the first color, the result of obtaining the density of each patch of the first density pattern image, The number of patches is set to N (N ≦ M, where N is a positive integer) by thinning out a gradation value area where there is no significant difference in density difference or a gradation value area where the density value is regarded as a straight line. Forming a second density pattern image on the image carrier,
An automatic gradation correction method for correcting gradation characteristics based on the image density of the first density pattern image and the image density of the second density pattern image. The number N of the patch of the second density pattern image, the number of the first density pattern at least one patch image density can be interpolated using images smaller than the number M of the patch of the first density pattern image The automatic gradation correction method according to claim 4 . Image density of the second density pattern image can be interpolated using the image density of the first density pattern image is interpolated from a concentration of at least two patches of the first density pattern image, and the density of the two patches The automatic gradation correction method according to claim 5 , wherein are different densities.

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