JP5375682B2 - Image forming apparatus, image forming method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, an image forming method and a program, which compensate variation in image density between image forming apparatuses when a plurality of image forming apparatuses are used. <P>SOLUTION: The image forming apparatus includes: an image forming means for forming a test pattern showing a plurality of densities by using test pattern data corresponding to a target density; a detection means for detecting the density of the test pattern formed by the image forming means; a calculating means for calculating correction parameters regarding the density correction of the image data based on densities detected by the detection means and the target density; a storing means for storing a characteristic value shown by the density of the test pattern which is detected by the detection means and the reference characteristic value shown by the density of the test pattern that is detected by a reference unit; and a control means for normalizing the correction parameter based on the characteristic values and the reference characteristic value and then causing the image forming means to form the image data with density correction applied by using the normalized correction parameter. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus, an image forming method, and a program for automatically correcting density fluctuations.

  An image forming apparatus such as a copying machine, a printer, or a facsimile machine exposes image light corresponding to image data onto a photoconductor that has been charged in advance by a charger, thereby forming a latent image on the photoconductor, Development is performed by supplying a powder developer (toner) from the developing unit and attaching the toner. It is transferred onto a transfer belt, and an image is formed on the transfer paper by feeding the transfer paper between the transfer belt and the transfer unit.

  In an image forming apparatus that forms a plurality of color images, a latent image of each color image is separately formed, separately developed, and a plurality of color image images are superimposed to form a plurality of color images. For this reason, a photoreceptor, a charger, a developing unit, and the like are separately required for each color. The developing unit includes a plurality of toner cartridges containing toner as a developing device, and when forming an image of each color, the toner of each color is supplied from each toner cartridge.

  In such an image forming apparatus, density fluctuation occurs when the power is turned on or after a large amount of printing is performed. In order to print at a constant density, it is necessary to measure the density and perform density correction. Therefore, an apparatus including a density sensor for measuring density, and a control unit that corrects the density value obtained by the density sensor, calculates a correction parameter, and gives the correction parameter to form a density-corrected image. Proposed to achieve highly accurate gradation correction. Further, the correction timing, the test pattern for correction, and the density range to be corrected have been improved, and an apparatus that has improved these has been proposed.

  For example, by forming a pattern on each of the recording material and holding the image, and correcting the image density using these two patterns, short-term image density fluctuation and long-term image density fluctuation A technique for correcting both of these is disclosed (see Patent Document 1).

  By the way, due to the property that a density sensor is an industrial product, its characteristics (density detection characteristics) are generally different for each individual. Since the density correction depends on the density detection characteristics of the density sensor, when image data is printed by a plurality of image forming apparatuses, the image density of the formed image varies depending on the characteristics of each density sensor. There is a problem that arises. Note that the technique of Patent Document 1 cannot deal with the above-mentioned problem because it is intended for density fluctuations in the image forming apparatus alone.

  The present invention has been made in view of the above, and an image forming apparatus and an image forming method capable of compensating for variations in image density among image forming apparatuses that occur when a plurality of image forming apparatuses are used. And to provide a program.

  In order to solve the above-described problems and achieve the object, the present invention is an image forming apparatus that forms an image by performing density correction on image data, and uses a plurality of test pattern data corresponding to the target density. Image forming means for forming a test pattern representing the density of the image, detection means for detecting the density of the test pattern formed by the image forming means, each density detected by the detection means, and a target of the test pattern data Based on the density, a calculation means for calculating a correction parameter related to the density correction of the image data, a characteristic value represented by the density of the test pattern detected by the detection means, and a reference device used as a reference Storage means for storing a reference characteristic value represented by the density of the test pattern, and normalizing the correction parameter based on the characteristic value and the reference characteristic value. The image data subjected to density correction using the correction parameter ized, characterized by comprising a control means for forming on said image forming means.

  The present invention is also an image forming method executed by an image forming apparatus that forms an image by performing density correction on image data, and the image forming means uses a plurality of test pattern data corresponding to a target density. A test pattern forming process for forming a test pattern representing the density of the test pattern; a detecting process for detecting the density of the test pattern formed in the test pattern forming process; and a calculating means for detecting the test pattern. And calculating means for calculating a correction parameter for correcting the density of the image data based on each density and the target density of the test pattern, and the control means represents the density of the test pattern detected in the detection process. The correction parameter is normalized based on the characteristic value and the reference characteristic value represented by the density of the test pattern detected by a reference device as a reference. And, the image data subjected to the density correction using the correction parameters this normalization, and a control step of forming on the imaging means.

  Further, the present invention provides an image forming device for forming a test pattern representing a plurality of densities using test pattern data corresponding to a target density, using a computer of an image forming apparatus that forms an image by performing density correction on the image data. And density correction of the image data based on each density detected by the detection means and a target density of the test pattern based on the detection means for detecting the density of the test pattern formed by the imaging means. A calculating means for calculating the correction parameter, a characteristic value representing the density of the test pattern detected by the detecting means, and a reference characteristic value representing the density of the test pattern detected by a reference apparatus serving as a reference. And normalizing the correction parameter based on the correction parameter, and causing the image forming unit to form image data subjected to density correction using the normalized correction parameter. And control means, is to function.

  According to the present invention, the correction parameter is normalized using the characteristic value of the detection unit included in the image forming apparatus of the image forming apparatus and the reference characteristic value of the reference apparatus serving as a reference, and the image is subjected to density correction using the normalized correction parameter. Print the data. As a result, even when a plurality of image forming apparatuses are used, the correction parameter of each image forming apparatus can be normalized based on a common reference density detection characteristic. It is possible to compensate for variations in density.

FIG. 1 is a diagram schematically illustrating a configuration of an image forming system. FIG. 2 is a block diagram showing an example of the configuration of the image forming apparatus shown in FIG. FIG. 3 is a diagram showing each functional unit related to the image forming process in the image forming apparatus shown in FIG. FIG. 4 is a diagram schematically illustrating the configuration of the image forming unit. FIG. 5 is a diagram showing the relationship between the density detection characteristic of the test pattern detected by the density sensor and the density characteristic represented by the target density data itself. FIG. 6 is a diagram showing a correction gamma for correcting the density detection characteristic of FIG. 5 to a target density. FIG. 7 is a diagram showing density detection characteristics of the density sensor mounted on each image forming apparatus. FIG. 8 is a diagram showing an example of density detection characteristics of the test pattern detected by the density sensor of each image forming apparatus. FIG. 9 is a diagram illustrating an example of the correction gamma generated by each image forming apparatus. FIG. 10 is a diagram illustrating an example of the normalized correction gamma calculated by each image forming apparatus. FIG. 11 is a flowchart illustrating a procedure of reference device setting processing executed by the control unit of the image forming apparatus serving as the reference device. FIG. 12 is a flowchart illustrating a procedure of image density correction processing executed by the control unit of each image forming apparatus. FIG. 13 is a diagram illustrating an example of the relationship between the density variation of each image forming apparatus and the start timing of the image density correction process. FIG. 14 is a flowchart illustrating a procedure of synchronization processing performed between the main image forming apparatus and the sub image forming apparatus. FIG. 15 is a diagram illustrating an example of the relationship between the density variation of each image forming apparatus synchronized by the synchronization process of FIG. 14 and the start timing of the image density correction process.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of an image forming apparatus, an image forming method, and a program according to the invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the embodiment shown in the drawings.

[First Embodiment]
FIG. 1 is a diagram schematically showing a configuration of an image forming system including an image forming apparatus according to a first embodiment of the present invention. As shown in FIG. 1, the image forming system includes a plurality of image forming apparatuses 1 to 4 and a terminal device 5, and the apparatuses are connected to each other via a network N so as to communicate with each other. Note that the number of devices connected to the network N is not limited to this figure.

  The image forming apparatuses 1 to 4 are image forming apparatuses such as a printer and a multifunction peripheral that form (print) information such as images and characters on recording paper (recording medium). The terminal device 5 is an information processing device such as a PC (Personal Computer) operated by a user who uses the image forming system.

  In the image forming system, when the image forming apparatuses 1 to 4 receive image data or character data transmitted from the terminal device 5, the image forming apparatus 1 stores information such as images represented by the data under the control of the control unit 30 described later. Formed (printed). The configurations of the image forming apparatuses 1 to 4 are the same. Hereinafter, when the image forming apparatuses 1 to 4 are not distinguished, they are simply referred to as “image forming apparatuses”.

  FIG. 2 is a block diagram showing an example of the configuration of the image forming apparatus shown in FIG. This image forming apparatus includes an image forming unit 10 that forms a test pattern formed in a predetermined shape and with a predetermined density on a medium M such as a photosensitive drum, an intermediate transfer member, and a recording sheet, which will be described later, and a formed test. A density sensor 20 that detects the density of a pattern as a detected density value, a printer panel 41 that displays various information, and allows a user to input a reference device to be described later, and a printer panel (UI) 40 are provided. A control unit 30 that calculates a normalization correction gamma, which will be described later, based on the selection content input via the control unit 30, gives the normalization correction gamma to the image forming unit 10 that forms an image, and forms a density-corrected image; And a communication control unit 42 that controls communication with other devices connected to the network N.

  Furthermore, a storage unit is provided for storing target density data in which a target density value indicating a density to be a control target is associated with a target parameter used to form an image of that density. The storage unit may be the NVRAM 37 of the control unit 30 or may be configured as an external storage medium.

  The image creating unit 10 receives the image data transmitted from the terminal device 5 and forms an image on the medium M. Further, the image forming unit 10 receives pattern data for density detection from the control unit 30 and, as a test pattern representing a plurality of densities on the medium M, a test pattern with a predetermined density or a plurality of test patterns with constant density steps. Form. Here, the medium M is a concept including not only printing paper but also a photosensitive drum and an intermediate transfer member, which will be described later. Note that FIG. 2 shows that three sets of rectangular test patterns are formed on the medium M, with four sets as one set, with constant density increments. These test patterns can form a test pattern having a predetermined density by setting a predetermined target density value.

  Note that the test pattern itself may be formed in all gradations (for example, 256 gradations in the case of 8 bits), or may be formed by thinning out in order to reduce toner consumption. Note that when thinning is performed, in order to compensate for the gradation of the thinned portion, spline interpolation or the like is employed, and processing is performed so that the gradation characteristics become smooth.

  The image forming unit 10 can be composed of an exposure device, a charger, a photoreceptor, a developing unit, a transfer belt, a transfer unit, and the like. As described above, the exposure apparatus exposes the image light corresponding to the image data onto the photoreceptor that has been charged in advance by the charger. The developing unit develops by supplying a powder developer (toner) from the developing unit to the photoreceptor on which a latent image is formed by exposure, and attaching the toner. The image is transferred onto the transfer belt, and paper is fed between the transfer belt and the transfer unit, thereby forming an image on the paper. The configuration of the image forming unit 10 will be described later.

  The density sensor 20 detects the density represented by the test pattern formed on the medium M as a density detection characteristic. The detected density detection characteristic is stored in the own apparatus density detection characteristic table 36 as an own apparatus density detection characteristic described later. If there is no density variation, the detected density detection characteristic is a value that matches the target density detection characteristic (target density data). However, density fluctuation occurs when the power is turned on or after printing in large quantities, and the density detection characteristic and the target density data are different values. In such a case, correction of density fluctuation (hereinafter referred to as density fluctuation correction) is required. The density sensor 20 includes a light source and a light receiving sensor, and the light emitted from the light source is reflected by the test pattern, the reflected light is received by the light receiving sensor, and the density is detected from the received light amount. Examples of the light source include LED, LD (laser diode), EL, cold cathode tube, and light bulb. Examples of the light receiving sensor include PD (photodiode) and CCD.

  Since the detected density value detected by the density sensor 20 is an analog signal, the control unit 30 has an A / D conversion unit 31 that converts the analog signal into a digital signal, and correction that controls to execute the density correction process. A processing control unit 32, a panel control unit 33 functioning as an interface for controlling an input signal from the printer panel 41 and an output signal to the printer panel 41, and a pattern for generating a test pattern having a predetermined shape and a predetermined density as pattern data A data generation unit 34, a reference density detection characteristic table 35 that stores reference density detection characteristics to be described later, an own apparatus density detection characteristic table 36 that stores density detection characteristics of the density sensor 20 included in the image forming apparatus, and a CPU 39 NVRA that stores a predetermined program to be executed and setting information such as target density data 37, it includes a ROM38 storing a predetermined program CPU39 executes, a CPU39 for controlling the entire control unit 30.

  The control unit 30 calculates a correction parameter (hereinafter referred to as correction gamma) related to density variation correction using the own apparatus density detection characteristic stored in the own apparatus density detection characteristic table 36 and the target density data. Further, the control unit 30 uses the reference density detection characteristic stored in the reference density detection characteristic table 35 and the own apparatus density detection characteristic stored in the own apparatus density detection characteristic table 36 in another image forming apparatus. In order to compensate for variations in density detection characteristics of the density sensor 20, a normalized correction gamma, which will be described later, is generated by normalizing (correcting) the correction gamma. Then, the control unit 30 sets the normalized correction gamma in a gamma table 53a described later in order to cause the image forming unit 10 to form a density-corrected image.

  In order to execute the density correction process to which the normalized correction gamma is applied, the correction process control unit 32 reads a program for the CPU 39 to execute the process from the ROM 38 and executes the program. The pattern data generation unit 34 generates pattern data corresponding to the target density, and sends the pattern data to the image forming unit 10 at a predetermined timing, so that the image forming unit 10 forms a test pattern on the medium M.

  The density sensor 20 detects the formed test pattern and sends it to the A / D conversion unit 31. The A / D conversion unit 31 converts the analog signal into a digital signal. Thereafter, the correction parameter is calculated using the detected density value that is a digital signal and the target density value and the target parameter stored in the storage unit.

  FIG. 3 is a diagram showing functional units related to image formation in the image forming apparatus shown in FIG. The applications and modules are executed by the CPU 39, thereby executing image input / output processing, conversion processing, and the like. For ease of explanation, the application and modules are described here as being performed by the application and modules. To do.

  The application 50 sends the image data to the color matching module 51 as RGB signals. When the application 50 is a scanner application or a copy application, the application 50 reads an image and outputs it as image data. The color matching module 51 converts RGB signals into CMYK signals. The RGB signal is a signal composed of basic three primary colors of red (R), green (G), and blue (B), and the CMYK signal is cyan (C), magenta (M), yellow (Y), and black (K). It is the signal which consists of.

  The color matching module 51 uses the color profile 52 at the time of conversion. The color profile 52 includes data necessary for converting color gamut values, and includes information on color, hue, vividness, and brightness. The color profile 52 can include an LUT 52a and an IN / OUTPUT table 52b which are input / output correspondence tables.

  The CMYK signal is sent to the gamma conversion module 53 and converted into a gamma value. The gamma value is a numerical value used when representing the tone response characteristics of the image, and is converted using the gamma table 53a.

  The gamma value of CMYK is sent to the total amount regulation module 54, and the total amount of toner is determined using the total amount regulation value 54a. The gamma value of CMYK whose total amount is restricted is sent to a gradation conversion module 55 that performs binarization using the dither pattern 55a. After being binarized by the gradation conversion module 55, it is sent to the image forming unit 10, and an image in which the gradation of the image is expressed in gradation by a dither pattern (knitting point) is formed.

  Hereinafter, the configuration of the image forming unit 10 and the image forming process when the image forming apparatus is a laser beam type printer will be described with reference to FIG. Here, FIG. 4 is a diagram schematically illustrating the configuration of the image forming unit 10.

  As shown in FIG. 4, the image forming unit 10 includes a laser light source 101, a photosensitive drum 102, a developing unit 103, an intermediate transfer member 104, a conveyance belt 105, a transfer unit 106, and a fixing unit 107. I have.

  An image is formed on the photosensitive member of the photosensitive drum 102 by the laser beam emitted from the laser light source 101 (latent image forming process), and the image formed by the toner supplied from the developing unit 103 is visualized (developing process). ). Hereinafter, the visualized image is referred to as a toner image.

  The toner image on the photosensitive drum 102 is transferred to the intermediate transfer member 104, and further transferred by the transfer unit 106 onto the printing paper 108 fed by the transport belt 105 (transfer process). In the case of full-color printing, the processes of “latent image formation”, “development”, and “transfer” are performed for the colors to be used.

  The printing paper 108 to which the toner image has been transferred is sent to the fixing unit 107 by the conveying belt 105, and the toner image is fixed on the printing paper 108 by heat melting (fixing process), whereby an image is formed on the printing paper 108. Will be. The density sensor 20 is provided in the vicinity of the photosensitive drum 102 and the intermediate transfer member 104, and is configured to detect the density of the toner image formed on the photosensitive drum 102 or the intermediate transfer member 104. .

  The test pattern described above is formed as a toner image on the photosensitive drum 102 and the intermediate transfer member 104 as the medium M. The density (density detection characteristic) of the test pattern detected by the density sensor 20 is input to the control unit 30 described above for density correction. Hereinafter, the principle of density correction by the control unit 30 will be described with reference to FIGS. 5 and 6.

  FIG. 5 is a diagram showing the relationship between the density detection characteristic of the test pattern detected by the density sensor 20 and the density characteristic represented by the target density data itself. In the figure, a curve L1 indicates the density detection characteristic of the test pattern detected by the density sensor 20, and a curve L2 indicates the density characteristic of the target density data.

  It is preferable that the density detection characteristic matches the density characteristic of the target density data. Therefore, as shown in FIG. 5, when the density detection characteristic is lower than the density characteristic of the target density data, the control unit 30 calculates a convex correction gamma GC corresponding to the difference, and is shown in FIG. By applying to the currently set gamma G (hereinafter referred to as current gamma), the density characteristic of the curve L1 is corrected to become the curve L2. Here, FIG. 6 is a diagram showing a correction gamma for correcting the density detection characteristic of FIG. 5 to the target density, and shows the relationship between the current gamma G and the correction gamma GC. It is assumed that the correction gamma of the portion other than the density represented by the test pattern is derived by a known interpolation method such as spline interpolation.

  By the way, due to the property that the concentration sensor 20 is an industrial product, it is common that the characteristics for detecting the concentration vary among individuals. For example, when the same test pattern formed on the photosensitive drum 102 or the intermediate transfer member 104 is detected by the density sensor 20 mounted on each of the image forming apparatuses 1 to 4, as shown in FIG. 20 does not necessarily indicate the same density detection characteristic.

  Here, FIG. 7 is a diagram illustrating an example of density detection characteristics of the density sensor 20 mounted in each of the image forming apparatuses 1 to 4. In the figure, a curve L11 shows the density detection characteristic of the density sensor 20 mounted on the image forming apparatus 1, and shows an ideal characteristic. A curve L12 indicates the density detection characteristic of the density sensor 20 mounted on the image forming apparatus 2. The curve L12 shows an ideal value for the maximum density, but the characteristics of the highlight portion and the shadow portion are shifted. A curve L13 indicates the density detection characteristic of the density sensor 20 mounted on the image forming apparatus 3. In the curve L13, the maximum density tends to be detected low, and accordingly the density is detected as a whole low. A curve L14 indicates the density detection characteristic of the density sensor 20 mounted on the image forming apparatus 4. In the curve L14, the maximum density tends to be detected high, and accordingly the density is detected as a whole high.

  When the density of the test pattern formed on the photosensitive drum 102 or the intermediate transfer body 104 is measured by the density sensor 20 of each of the image forming apparatuses 1 to 4, the result is expressed as shown in FIG. Here, FIG. 8 is a diagram showing an example of the density detection characteristic of the test pattern detected by the density sensor 20 of each image forming apparatus. In the figure, a curve L21 indicates the density detection characteristic of the density sensor 20 mounted on the image forming apparatus 1, a curve L22 indicates the density detection characteristic of the density sensor 20 mounted on the image forming apparatus 2, and a curve L23 indicates the image. The density detection characteristic of the density sensor 20 mounted on the forming apparatus 3 is shown, and the curve L24 shows the density detection characteristic of the density sensor 20 mounted on the image forming apparatus 4.

  When the control unit 30 of each image forming apparatus calculates the correction gamma based on the density detection characteristics shown in FIG. 8, the result is expressed as shown in FIG. Here, FIG. 9 is a diagram illustrating an example of the correction gamma generated by each image forming apparatus. In FIG. 9, a curve GC11 is a correction gamma in the image forming apparatus 1, a curve GC12 is a correction gamma in the image forming apparatus 2, a curve GC13 is a correction gamma in the image forming apparatus 3, and a curve GC14 is in the image forming apparatus 4. The correction gamma of each is shown. In the image forming apparatus 1, since the density detection characteristic matches the ideal density data, the curve GC11 is the same as the current gamma G.

  When density correction is executed using the correction gamma of FIG. 9, it can be said that the density correction is correctly performed when considered for each image forming apparatus, but when comparing the density characteristics between the image forming apparatuses, FIG. The density of the formed image is also shifted according to the variation in the characteristics of the density sensors shown.

  For this reason, the control unit 30 of each image forming apparatus has a density detection characteristic (hereinafter referred to as a reference) of the density sensor 20 mounted on one of the image forming apparatuses 1 to 4 as a reference (hereinafter referred to as a reference apparatus). The correction gamma is further corrected by using the density detection characteristic) and the density detection characteristic of the density sensor 20 included in the image forming apparatus image of itself (hereinafter, the own apparatus density detection characteristic).

Specifically, the control unit 30 substitutes the reference density detection characteristic and the own apparatus density detection characteristic into the following equation (1) to normalize the correction gamma, thereby varying the density detection characteristic in each image forming apparatus. Compensated correction gamma (hereinafter referred to as normalized correction gamma) is calculated. In the following formula (1), “correction gamma” is the correction gamma GC described with reference to FIG.
Normalized correction gamma = correction gamma × (reference density detection characteristic / own apparatus density detection characteristic) (1)

  Since the normalized correction gamma obtained by the above equation (1) is normalized based on the reference density detection characteristic common to each image forming apparatus, variations in density detection characteristics in each image forming apparatus are compensated. Yes. Therefore, in each image forming apparatus, the image data that has been subjected to density correction using the normalized correction gamma is obtained by compensating for variations in image density between the image forming apparatuses.

  FIG. 10 is a diagram illustrating an example of the normalized correction gamma calculated by each of the image forming apparatuses 1 to 4 when the density sensor 20 of the image forming apparatus 1 is used as a reference. In FIG. 10, a curve GC21 is a normalized correction gamma in the image forming apparatus 1, a curve GC22 is a normalized correction gamma in the image forming apparatus 2, and a curve GC23 is a normalized correction gamma in the image forming apparatus 3. The GC 24 indicates the normalized correction gamma in the image forming apparatus 4. In the image forming apparatus 1, since the density detection characteristic in its own apparatus is the reference density detection characteristic, the normalized correction gamma and the correction gamma have the same value.

  By the way, in the normalized correction gamma calculated by the above equation (1), it can be said that the monotonously increasing output value with respect to the input (no reversal occurs) is superior in terms of gradation and high image quality. However, in practice, the density fluctuation is likely to occur in the highlight portion and the high density portion close to the background portion, and there is a possibility that the original correction gamma itself is reversed instead of monotonously increasing. In that case, the normalization correction gamma calculated by the above equation (1) itself also reverses, resulting in a problem that a gradation step occurs in the image.

  Therefore, in order to avoid this, the control unit 30 of each image forming apparatus corrects the reversal and corrects the correction gamma with a monotonically increasing shape when the reversal of the gradation occurs in the original correction gamma. To correct. Note that a known technique is used as a method for correcting a monotonically increasing shape. In this embodiment, the image forming apparatus 1 is used as a reference apparatus. However, the present invention is not limited to this, and an image forming apparatus mainly used by a user may be used as a reference, or the reference apparatus may be changed each time.

  Next, with reference to FIG. 11 and FIG. 12, processing relating to density correction executed by the control unit 30 of each image forming apparatus will be described.

  Here, FIG. 11 is a flowchart showing the procedure of the reference device setting process executed by the control unit 30 of the image forming apparatus serving as the reference device. First, when the control unit 30 receives an instruction from the user to use the image forming apparatus as a reference device (step S11), the control unit 30 detects the reference density using the density detection characteristic of the density sensor 20 of the image forming apparatus as a reference density detection characteristic. It memorize | stores in the characteristic table 35 (step S12).

  It should be noted that the selection of the reference device can be set by the user on the printer panel 41 on each image forming apparatus or the host computer 500 connected to the image forming apparatus. Further, at the time of step S12, the density detection characteristic stored in the own apparatus density detection characteristic table 36 may be re-stored in the reference density detection characteristic table 35, or a test pattern may be formed in the image forming unit 10, The density detection characteristic may be newly acquired.

  Subsequently, the image forming apparatus notifies other image forming apparatuses that the image forming apparatus of its own has been selected as the reference apparatus (step S13), and the reference density detection characteristics stored in the reference density detection characteristic table 35. Alternatively, the reference density detection characteristic stored in the own apparatus density detection characteristic table 36 is transmitted to another image forming apparatus (step S14), and the process ends.

  The control unit 30 of the image forming apparatus that has received the notification of selection of the reference device stores the density detection characteristic transmitted together with this notification in the reference density detection characteristic table 35. As a result, each image forming apparatus can normalize the correction gamma using the common reference density detection characteristic.

  FIG. 12 is a flowchart illustrating a procedure of image density correction processing executed by the control unit 30 of the reference apparatus and other image forming apparatuses other than the reference apparatus. As a premise of this processing, it is assumed that correction gamma is stored in advance in the gamma table 53a.

  First, when executing density correction (generation of correction gamma), the control unit 30 stores the reference density detection characteristic stored in the reference density detection characteristic table 35 and the own apparatus stored in the own apparatus density detection characteristic table 36. The density detection characteristic (self apparatus density detection characteristic) is read (step S21).

  Here, it is assumed that the density detection characteristics of the density sensor 20 are preset when the image forming apparatus is shipped from the factory, but it is assumed that the density detection characteristics themselves fluctuate with time due to user use. Therefore, it is preferable to provide a mechanism that can reset the density detection characteristics of the density sensor. Specifically, when the image forming apparatus is started up or a predetermined number of sheets are output, control is performed so that a test pattern is formed on the photosensitive drum 102 or the intermediate transfer member 104, and the density detection of the test pattern detected by the density sensor 20 is performed. It can be realized by controlling to automatically store the characteristics.

  Next, the control unit 30 normalizes the correction gamma stored in the gamma table 53a using the reference density detection characteristic and the own apparatus density detection characteristic read in step S21 based on the above formula (1). Normalized correction gamma is generated (step S22). At this time, if the correction gamma is reversed, this is corrected to generate a normalized correction gamma having a monotonically increasing shape.

  Then, the control unit 30 sets the normalized correction gamma in the gamma table 53a, and causes the image forming unit 10 to print the image data subjected to density correction using the normalized correction gamma (step S23). As described above, in this processing, the density correction of the image data is performed using the normalized correction gamma normalized based on the reference density detection characteristic, so that the density of the image formed by each image forming apparatus is equal.

  As described above, according to the present embodiment, the correction gamma is normalized using the density detection characteristic of the density sensor 20 included in the image forming apparatus and the reference density detection characteristic serving as a reference. Print the image data corrected for density. Thus, even when a plurality of image forming apparatuses are used, the correction gamma of each image forming apparatus can be corrected (normalized) based on the common reference density detection characteristics. It is possible to compensate for variations in image density.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In general printing, printing is performed from the terminal device 5 using one image forming apparatus. However, when printing a large number of copies, it is conceivable to perform printing using a plurality of image forming apparatuses. In this case, it is only necessary to instruct each image forming apparatus to print a document to be printed. However, since it is necessary to specify the number of copies and the paper size for each image forming apparatus, the procedure until printing is complicated. Therefore, conventionally, a printing method has been realized in which a plurality of image forming apparatuses can perform printing in cooperation by only specifying the number of copies and the document size once. Hereinafter, this printing method is referred to as a load distribution mode.

  In the load distribution mode, the most frequently used image forming apparatus (hereinafter referred to as a main image forming apparatus) generates correction gamma for each predetermined number of output sheets. That is, regeneration of the correction gamma is frequently executed. However, an image forming apparatus used as a sub unit other than the main image forming apparatus (hereinafter referred to as a sub image forming apparatus) does not print as frequently as the main image forming apparatus, and therefore has a corrected gamma as compared with the main image forming apparatus. The number of generations is reduced.

  Since density fluctuations occur with time and the increase in the number of output sheets, if density correction is performed at a timing specific to each image forming apparatus, the degree of density fluctuation may be different for each image forming apparatus. For example, assuming that density fluctuations occurring in the image forming apparatuses 1 to 4 shown in FIG. 1 are represented by the graph of FIG. 13, density fluctuation correction is performed at different times due to differences in the number of output sheets. In this case, depending on the timing at which printing is performed in the load distribution mode, generation and printing of the normalization correction gamma is performed with the old correction gamma before the density variation correction, so that the density when the image data is output is the image forming apparatus. It will be different between. FIG. 13 is a diagram illustrating the density fluctuation characteristics of the image forming apparatuses 1 to 4, where the horizontal axis represents time and the vertical axis represents the density of the output image data. Also, the circles in the figure represent the timing at which density variation correction is performed in each of the image forming apparatuses 1 to 4.

  Therefore, in this embodiment, by synchronizing the start timing of density fluctuation correction performed in the main image forming apparatus and the start timing of density fluctuation correction performed in the sub image forming apparatus, image data is stored in each image forming apparatus. Control is performed so that the density when output is substantially equal.

  Specifically, the control unit 30 of each image forming apparatus determines whether its own image forming apparatus is a main image forming apparatus or a sub image forming apparatus. In addition to starting the density fluctuation correction at a timing specific to each, a signal (processing start signal) for notifying the start of density fluctuation correction is transmitted to another image forming apparatus (sub-image forming apparatus). In addition, when the control unit 30 determines that its own image forming apparatus is a sub-image forming apparatus, the control unit 30 starts density variation correction at a timing when a processing start signal is received from the main image forming apparatus.

  Information indicating whether each image forming apparatus is a main image forming apparatus or a sub image forming apparatus is held in advance in a storage medium such as NVRAM 37 included in each image forming apparatus, but is not limited thereto. To do. For example, the terminal device 5 may be configured to hold information indicating whether each image forming apparatus is a main image forming apparatus or a sub image forming apparatus, or information indicating the use frequency of each image forming apparatus may be stored. The image forming apparatuses may be shared or held among the image forming apparatuses, and based on the use frequency, it may be determined whether the image forming apparatus is the main image forming apparatus or the sub image forming apparatus.

  Hereinafter, the flow of synchronization processing related to density fluctuation correction performed between the main image forming apparatus and the sub image forming apparatus will be described with reference to FIG. FIG. 14 is a flowchart illustrating a procedure of synchronization processing performed between the main image forming apparatus and the sub image forming apparatus. As a premise of this process, it is assumed that the reference device setting process described in FIG. 11 has already been performed. Further, it is assumed that the determination between the main image forming apparatus and the sub image forming apparatus in the load distribution mode has already been made.

  First, the control unit 30 of the main image forming apparatus waits until the start of density fluctuation correction (step S31; No). When this start time is reached (step S31; Yes), the process starts toward the sub image forming apparatus. A signal is transmitted (step S32). Next, the control unit 30 of the main image forming apparatus corrects the density variation based on the density detection characteristic (self apparatus density detection characteristic) of the test pattern newly formed on the medium M and the density characteristic of the target density data, that is, Regeneration of the correction gamma is started (step S33).

  On the other hand, the control unit 30 of the sub-image forming apparatus waits for execution of density fluctuation correction until a process start signal is transmitted from the main image forming apparatus (step S41; No), and receives this process start signal (step S41). Yes), density variation correction is started based on the density detection characteristics of the test pattern formed on the medium M and the density characteristics of the target density data (step S42).

  When the main image forming apparatus is the reference apparatus, the control unit 30 of the main image forming apparatus (reference apparatus) notifies the sub-image forming apparatus that the image forming apparatus is the reference apparatus after step S33. At the same time, the reference density detection characteristic stored in the reference density detection characteristic table 35 or the reference density detection characteristic stored in the own apparatus density detection characteristic table 36 is transmitted to another image forming apparatus. As a result, the control unit 30 of the image forming apparatus that has received the notification of the selection of the reference device stores the density detection characteristic transmitted together with this notification in the reference density detection characteristic table 35.

  If one of the sub-image forming apparatuses is a reference apparatus, the control unit 30 of the sub-image forming apparatus (reference apparatus) may indicate that the own image forming apparatus has been selected as the reference apparatus after step S42. And the reference density detection characteristic stored in the reference density detection characteristic table 35 or the reference density detection characteristic stored in the own apparatus density detection characteristic table 36 is transmitted to another image forming apparatus. To do. As a result, the control unit 30 of the image forming apparatus that has received the notification of the selection of the reference device stores the density detection characteristic transmitted together with this notification in the reference density detection characteristic table 35.

  For example, it is assumed that among the image forming apparatuses 1 to 4 illustrated in FIG. 1, the image forming apparatus 1 is a main image forming apparatus, and the image forming apparatuses 2 to 4 are sub image forming apparatuses. In this case, since the image forming apparatuses 2 to 4 start the density fluctuation correction in response to the processing start signal from the image forming apparatus 1, as shown in FIG. 15, the start timing of the density fluctuation correction of the image forming apparatus 1 is synchronized. Then, the density fluctuation correction is started. FIG. 15 is a diagram illustrating the density fluctuation characteristics of the image forming apparatuses 1 to 4 that perform the synchronization processing of FIG. 14, where the horizontal axis represents time and the vertical axis represents the density of the output image data. Represents. Also, the circles in the figure represent the timing at which density fluctuation correction is performed in each image forming apparatus.

  As described above, according to the second embodiment, the start timing of density fluctuation correction performed in the main image forming apparatus and the sub image in the load distribution mode in which a plurality of image forming apparatuses perform printing in cooperation. Since the start timing of the density fluctuation correction performed by the forming apparatus can be synchronized, it is possible to control so that the densities when the image data is output by each image forming apparatus are substantially equal. Further, between the main image forming apparatus and the sub image forming apparatus, the correction gamma of each image forming apparatus can be corrected (normalized) based on a common reference density detection characteristic. Variation in image density can be compensated.

  The embodiment according to the present invention has been described above, but the present invention is not limited to this, and various modifications, substitutions, additions, and the like are possible without departing from the spirit of the present invention.

  For example, in the above-described embodiment, the density detection characteristic (self apparatus density detection characteristic) of the density sensor 20 in each image forming apparatus is stored in advance. The printed test pattern may be actually printed and measured, and stored as density detection characteristics in the image forming apparatus. This is because, when a test pattern for measuring density detection characteristics is drawn on the photosensitive drum 102 or the intermediate transfer body 104, there is a possibility that the density fluctuation occurs in the test pattern itself. By actually printing and measuring the test pattern for measuring the density detection characteristic, not only the density fluctuation of the test pattern itself on the photosensitive drum 102 or the intermediate transfer body 104 can be absorbed, but also the density detection characteristic on the printing paper 108. Therefore, more effective density correction can be performed.

  In the above embodiment, the variation correction of one density sensor 20 mounted in each of a plurality of image forming apparatuses has been described. However, the present invention is not limited to this, and a plurality of density sensors are mounted in one image forming apparatus. In addition, the present invention can also be applied to the case where variations between these density sensors are corrected.

  It is also possible to provide a program related to the processing of the above embodiment as a computer-readable storage medium. The storage medium may be a computer-readable storage medium such as a magnetic disk, optical disk (CD-ROM, CD-R, DVD, etc.), magneto-optical disk (MO, etc.), semiconductor memory, etc. For example, the storage format may be any form.

  Further, the program according to the above-described embodiment may be configured to be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network.

  As described above, the image forming apparatus, the image forming method, and the program according to the present invention are useful for automatically correcting density fluctuations, and in particular, match the image densities of images formed by a plurality of image forming apparatuses. Suitable for cases.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image forming apparatus 3 Image forming apparatus 4 Image forming apparatus 5 Terminal apparatus 10 Image forming part 20 Density detection part 30 Control part 31 A / D conversion part 32 Correction process control part 33 Panel control part 34 Pattern data generation part 35 Reference density detection characteristic table 36 Self apparatus density detection characteristic table 37 NVRAM
38 ROM
39 CPU
41 Printer Panel 42 Communication Control Unit 50 Application 51 Color Matching Module 52 Color Profile 52a LUT
52b IN / OUTPUT table 53 Gamma conversion module 54 Total amount restriction module 54a Total amount restriction value 55 Gradation conversion module 55a Dither pattern 101 Laser light source 102 Photosensitive drum 103 Development unit 104 Intermediate transfer member 105 Conveyor belt 106 Transfer unit 107 Fixing unit 108 Printing Paper

Japanese Patent Laid-Open No. 10-039555

Claims (10)

An image forming apparatus that forms an image by performing density correction on image data,
Image forming means for forming a test pattern representing a plurality of densities using test pattern data corresponding to a target density;
Detecting means for detecting the density of the test pattern formed by the image forming means;
Calculation means for calculating a correction parameter relating to density correction of the image data based on each density detected by the detection means and a target density of the test pattern data;
Storage means for storing a characteristic value represented by the density of the test pattern detected by the detection means and a reference characteristic value represented by the density of the test pattern detected by a reference device serving as a reference;
Control means for normalizing the correction parameter based on the characteristic value and the reference characteristic value, and causing the image forming means to form image data subjected to density correction using the normalized correction parameter;
An image forming apparatus comprising:   The said control means normalizes the said correction data by integrating | accumulating the coefficient obtained by dividing the said reference | standard characteristic value by the said characteristic value on the said correction parameter, The said correction data are characterized by the above-mentioned. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit normalizes the correction parameter every time the reference characteristic value is updated.   The reference characteristic value is a characteristic value of the density of the test pattern detected by the detection unit included in the image forming apparatus set as a reference apparatus or other image forming apparatus other than the image forming apparatus. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. An input means for receiving an instruction input from a user;
When an instruction input using the image forming apparatus as a reference apparatus is received by the input unit, the characteristic value of the detection unit included in the image forming apparatus is notified to the other image forming apparatus as the reference characteristic value. Notification means to
The image forming apparatus according to claim 1, further comprising:   6. The image forming apparatus according to claim 5, further comprising a storage control unit that stores a reference characteristic value notified from another image forming apparatus other than the image forming apparatus of the apparatus in the storage unit. In a load distribution mode in which a plurality of image forming apparatuses including the own image forming apparatus perform printing in cooperation, the main image forming apparatus in which the own image forming apparatus is mainly used or a sub image forming apparatus used as a sub Determination means for determining whether or not
When the determination unit determines that the image forming apparatus is a main image forming apparatus, the test pattern forming unit starts generation of the test pattern, and notifies the sub image forming apparatus of the start of generation of the test pattern. A synchronization unit that causes the test pattern forming unit to start generating the test pattern in response to a generation start notification transmitted from the main image forming device when the unit determines that the image is a sub-image forming device;
The image forming apparatus according to claim 1, further comprising:   The synchronization means notifies the other apparatus as the reference characteristic value of the characteristic value detected by the detection means in accordance with the control of the test pattern forming means when the image forming apparatus of its own is the reference apparatus; 8. The storage unit stores a reference characteristic value notified from an image forming apparatus other than the own image forming apparatus when the own image forming apparatus is other than the reference apparatus. The image forming apparatus described. An image forming method executed by an image forming apparatus that forms an image by performing density correction on image data,
A test pattern forming step in which the image forming means forms a test pattern representing a plurality of densities using test pattern data corresponding to the target density;
A detecting step for detecting a density of the test pattern formed in the test pattern forming step;
A calculating step for calculating a correction parameter for correcting the density of the image data based on each density detected in the detecting step and the target density of the test pattern;
The control means determines the correction parameter based on the characteristic value representing the density of the test pattern detected in the detection step and the reference characteristic value represented by the density of the test pattern detected by a reference device serving as a reference. A control step of normalizing and causing the image forming means to form image data subjected to density correction using the normalized correction parameter;
An image forming method comprising: A computer of an image forming apparatus that performs density correction on image data to form an image,
Image forming means for forming a test pattern representing a plurality of densities using test pattern data corresponding to a target density;
Detecting means for detecting the density of the test pattern formed by the image forming means;
Calculation means for calculating a correction parameter relating to density correction of the image data based on each density detected by the detection means and a target density of the test pattern;
The correction parameter is normalized based on a characteristic value representing the density of the test pattern detected by the detection means and a reference characteristic value represented by the density of the test pattern detected by a reference device serving as a reference. Control means for causing the image forming means to form image data subjected to density correction using normalized correction parameters;
Program to make it function.

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