JP2007114593A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming an image with a satisfactory image quality and precisely calculating the amount of toner consumed for image formation. <P>SOLUTION: Output image data is scaled by data processing so that an output maximum gradation value is equal to or lower than a saturation start gradation value Lmax, at which an increase in image density relative to an increase in gradation value starts to saturate, in relation between the gradation value and image density. By processing data so that output image data with 0 to Lmax gradation is obtained from an input image data with 0 to 255 gradation, the ratio of the gradation value, expressed by the input image data to the image density becomes 1:1; and since the ratio of the gradation value to the amount of toner consumption becomes 1:1, image quality and accuracy in the calculation of an amount of toner consumption can be made compatible. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method for forming an image using toner.

  In an image forming apparatus that forms an image using toner, in order to obtain a predetermined image quality, data processing is performed on given multi-gradation image data, and an image is processed based on the image data after the data processing. Some are configured to form. For example, in the image forming apparatus described in Patent Document 1, the gamma characteristic of the apparatus is estimated from the density detection result of the patch image in which the gradation value is gradually changed, and a characteristic that cancels the gamma characteristic is given to the image data. As a result, an image can be formed with a good image quality without being affected by fluctuations in the gamma characteristic.

  Further, in this type of image forming apparatus, it is required to accurately calculate the amount of toner consumed for image formation in order to grasp the remaining amount of toner in the apparatus and manage consumables appropriately. For this purpose, for example, in the technique described in Patent Document 2, the gradation values of the print dots are integrated, and the toner consumption is calculated based on the integrated value.

JP 2004-077873 A JP 2002-162800 A

  The tone value represented by the image data is not necessarily proportional to the actual toner consumption. This is because there is a non-linear relationship between the toner amount constituting the image and the image density. In particular, as in the technique described in Patent Document 1 described above, when some characteristic is given to the image data itself for the purpose of improving the image quality, there is a large gap between the gradation value appearing by the image data and the toner consumption amount. Non-linearity occurs, which causes a problem that the calculation accuracy of the toner consumption is lowered.

  The present invention has been made in view of the above problems, and an object of the present invention is to form an image with a good image quality and to accurately calculate the amount of toner consumed to form the image.

  As a result of various experiments regarding the correlation between image data and toner consumption, the inventor of the present application has obtained the following knowledge. That is, in this type of image forming apparatus, when the density of the toner constituting the image (the amount of toner in a unit area) exceeds a certain level, the image density does not increase much even if the amount of toner is increased further. Under such circumstances, even if the image density is kept constant, the amount of toner constituting the image may not be uniquely determined. This is because image data is focused on only the image density or image quality. This is a cause of lowering the calculation accuracy of the toner consumption in the conventional technology that processes the toner.

  In view of the above, an image forming apparatus according to the present invention, in an image forming apparatus that forms an image using a built-in toner, performs predetermined data processing on multi-tone input image data corresponding to a toner color in order to achieve the above object. Data processing means for generating multi-tone output image data, image forming means for forming an image corresponding to the output image data, and toner consumed for image formation based on the input image data A toner consumption amount calculating means for calculating the amount of toner, and the data processing means performs the data processing so that a predetermined correlation is established between the input image data and the output image data, and Based on the relationship between the gradation value and the image density obtained in advance in the image forming means, the increase in the image density with respect to the increase in the gradation value is less than or equal to the saturation start gradation value at which saturation begins It is characterized by scaling the gray-scale value of the output image data.

  In order to achieve the above object, the image forming method according to the present invention performs data processing on multi-tone input image data corresponding to a toner color and has a predetermined correlation with the input image data. Data processing step for generating gradation output image data, an image forming step for forming an image corresponding to the output image data using toner, and a toner consumed for image formation based on the input image data A toner consumption amount calculating step for calculating the amount of toner, and in the data processing step, based on the relationship between the gradation value and the image density obtained in advance in the image forming step, an increase in image density with respect to an increase in gradation value Is characterized in that the gradation value of the output image data is scaled so as to be equal to or less than the saturation start gradation value at which the saturation starts.

  In the invention configured as described above, since the image density is not saturated with respect to the gradation value, the gradation value for realizing a certain image density is uniquely determined, and accordingly, to realize the density. The amount of toner required is also uniquely determined. Therefore, according to these inventions, it is possible to form an image with good image quality and to accurately determine the toner consumption based on the image data.

  For example, when data processing is performed such that output image data having a gradation value proportional to the gradation value of the input image data is generated, the toner consumption amount is also substantially proportional to the input image data. Therefore, in such a case, the toner consumption amount can be accurately obtained by integrating the gradation values of the input image data and calculating the toner consumption amount based on the integration value.

  In addition, when data processing is performed such that output image data having a predetermined gradation reproduction characteristic is generated for the gradation value of the input image data, the toner consumption also has the same characteristic as that of the input image data. To change. Therefore, in such a case, the gradation value of the input image data can be corrected and integrated based on the gradation reproduction characteristics, and the toner consumption amount can be calculated based on the integrated value.

  Here, for example, the saturation start gradation value can be determined based on the density detection result of the patch image formed by forming the patch image with each gradation value while changing the gradation value in multiple stages. More specifically, for example, the minimum value among the gradation values at which the increase in the density detection result of the patch image with respect to the increase in the gradation value is a predetermined threshold value or less can be set as the saturation start gradation value. As described above, by determining the saturation start gradation value based on the density detection result of the actually formed image, the image is formed without being affected by the characteristic variation of the apparatus and its change over time, and the toner consumption is calculated. be able to.

  FIG. 1 is a view showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus 1 forms a full color image by superposing four color toners (developers) of yellow (Y), cyan (C), magenta (M), and black (K), or black (K) toner. This is an image forming apparatus that forms a monochrome image using only the image forming apparatus. In the image forming apparatus 1, when an image signal is given to the main controller 11 from an external device such as a host computer, the engine controller 10 controls each part of the engine unit EG in accordance with a command from the main controller 11 to obtain a predetermined image. The forming operation is executed, and an image corresponding to the image signal is formed on the sheet S.

  In the engine unit EG, the photosensitive member 22 is provided to be rotatable in the arrow direction D1 in FIG. A charging unit 23, a rotary developing unit 4 and a cleaning unit 25 are arranged around the photosensitive member 22 along the rotation direction D1. The charging unit 23 is applied with a predetermined charging bias, and uniformly charges the outer peripheral surface of the photoconductor 22 to a predetermined surface potential. The cleaning unit 25 removes the toner remaining on the surface of the photosensitive member 22 after the primary transfer, and collects it in a waste toner tank provided inside. The photosensitive member 22, the charging unit 23, and the cleaning unit 25 integrally constitute the photosensitive member cartridge 2, and this photosensitive member cartridge 2 is detachably attached to the main body of the apparatus 1 as a whole.

  Then, the light beam L is irradiated from the exposure unit 6 toward the outer peripheral surface of the photosensitive member 22 charged by the charging unit 23. The exposure unit 6 exposes the light beam L onto the photosensitive member 22 in accordance with an image signal given from an external device, and forms an electrostatic latent image corresponding to the image signal.

  The electrostatic latent image thus formed is developed with toner by the developing unit 4. That is, in this embodiment, the developing unit 4 is configured as a support frame 40 that is rotatably provided about a rotation axis center orthogonal to the paper surface of FIG. A yellow developing device 4Y, a cyan developing device 4C, a magenta developing device 4M, and a black developing device 4K are provided. The developing unit 4 is controlled by the engine controller 10. Based on the control command from the engine controller 10, the developing unit 4 is driven to rotate, and the developing units 4Y, 4C, 4M, and 4K selectively face the photoconductor 22 with a predetermined gap therebetween. When positioned at a predetermined development position, the toner is applied to the surface of the photosensitive member 22 from a metal developing roller 44 that is provided in the developing unit and carries a charged toner of a selected color and is applied with a predetermined development bias. Is granted. As a result, the electrostatic latent image on the photosensitive member 22 is visualized with the selected toner color.

  Each of the developing devices 4Y, 4C, 4M, and 4K is provided with non-volatile memories 91 to 94 for storing information related to the developing devices. One of the connectors 49Y, 49C, 49M, and 49K provided in each developing device is selected as necessary, and the connector 109 provided on the main body side is connected to each other, and the CPU 101 of the engine controller 10 and the memory Communication is performed with 91-94. In this way, information about each developing device is transmitted to the CPU 101, and information in each of the memories 91 to 94 is updated and stored. Note that the communication between the CPU 101 and each of the memories 91 to 94 is not limited to that performed by mechanical contact using a connector as described above, and may be non-contact communication means such as wireless communication.

  The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. The transfer unit 7 includes an intermediate transfer belt 71 stretched between a plurality of rollers 72 to 75, and a drive unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction D2 by rotationally driving the roller 73. It has. When a color image is transferred to the sheet S, each color toner image formed on the photosensitive member 22 is superimposed on the intermediate transfer belt 71 to form a color image and taken out from the cassette 8 one by one. The color image is secondarily transferred onto the sheet S conveyed to the secondary transfer region TR2 along the conveyance path F.

  At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet S, the timing of feeding the sheet S to the secondary transfer region TR2 is managed. Specifically, a gate roller 81 is provided on the transport path F on the front side of the secondary transfer region TR2, and the gate roller 81 rotates in accordance with the timing of the circumferential movement of the intermediate transfer belt 71. S is sent to the secondary transfer region TR2 at a predetermined timing.

  Further, the sheet S on which the color image is thus formed is conveyed to the discharge tray portion 89 provided on the upper surface portion of the apparatus main body via the fixing unit 9, the pre-discharge roller 82 and the discharge roller 83. Further, when images are formed on both sides of the sheet S, when the rear end portion of the sheet S on which the image is formed on one side as described above is conveyed to the reversal position PR behind the pre-discharge roller 82. The rotation direction of the discharge roller 83 is reversed, whereby the sheet S is conveyed in the direction of the arrow D3 along the reverse conveyance path FR. Then, the sheet is again placed on the transport path F before the gate roller 81. At this time, the surface of the sheet S to which the image is transferred by contacting the intermediate transfer belt 71 in the secondary transfer region TR2 is first transferred. It is the opposite surface. In this way, images can be formed on both sides of the sheet S.

  Further, a density sensor 60 and a cleaner 76 are provided in the vicinity of the roller 75. The density sensor 60 optically detects the amount of toner constituting the toner image formed on the intermediate transfer belt 71 as necessary. That is, the density sensor 60 irradiates light toward the toner image, receives reflected light from the toner image, and outputs a signal corresponding to the reflected light amount. The cleaner 76 is configured to be able to come into contact with and separate from the intermediate transfer belt 71, and scrapes the residual toner on the belt 71 by contacting the intermediate transfer belt 71 as necessary.

  In addition, the apparatus 1 includes a display unit 12 controlled by the CPU 111 of the main controller 11 as shown in FIG. The display unit 12 is constituted by, for example, a liquid crystal display, and in accordance with a control command from the CPU 111, the operation guidance to the user, the progress of the image forming operation, the occurrence of an abnormality in the apparatus, the replacement timing of any unit, etc. A predetermined message for notification is displayed.

  In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112. Reference numeral 106 is a ROM for storing a calculation program executed by the CPU 101, control data for controlling the engine unit EG, and the like. Reference numeral 107 is a RAM for temporarily storing calculation results in the CPU 101 and other data. is there.

  Further, reference numeral 200 denotes a toner counter provided for calculating the amount of toner consumed for image formation. The configuration and operation of the toner counter 200 will be described in detail later.

  FIG. 3 is a diagram showing signal processing blocks in this apparatus. In this image forming apparatus, when an image signal is input from an external device such as the host computer 100, the main controller 11 performs predetermined signal processing on the image signal. The main controller 11 includes functional blocks such as a color conversion unit 114, a gradation correction unit 115, a halftoning unit 116, a pulse modulation unit 117, a gradation correction table 118, and a correction table calculation unit 119.

  In addition to the CPU 101, ROM 106, and RAM 107 shown in FIG. 2, the engine controller 10 includes a laser driver 121 for driving a laser light source provided in the exposure unit 6 and a detection result of the engine unit EG based on the detection result of the density sensor 60. A gradation characteristic detecting unit 123 that detects a gradation characteristic indicating a gamma characteristic is provided.

  In the main controller 11 and the engine controller 10, these functional blocks may be configured by hardware, or may be realized by software executed by the CPUs 111 and 101.

  In the main controller 11 to which the image signal is given from the host computer 100, the color conversion unit 114 converts the RGB gradation data indicating the gradation level of the RGB component of each pixel in the image corresponding to the image signal into the corresponding CMYK. Conversion into CMYK gradation data indicating the gradation level of the component. In this color conversion unit 114, the input RGB gradation data is, for example, 8 bits per pixel per color component (that is, representing 256 gradations), and the output CMYK gradation data is similarly 8 bits per pixel per color component ( That is, it represents 256 gradations). The CMYK gradation data output from the color conversion unit 114 is input to the gradation correction unit 115.

  The gradation correction unit 115 performs gradation correction on the CMYK gradation data of each pixel input from the color conversion unit 114. That is, the gradation correction unit 115 refers to the gradation correction table 118 registered in advance in the nonvolatile memory, and in accordance with the gradation correction table 118, the input CMYK gradation data of each pixel from the color conversion unit 114. Is converted into corrected CMYK gradation data indicating the corrected gradation level. The purpose of the gradation correction is to compensate for the change in the gamma characteristic of the engine unit EG configured as described above, and to keep the overall gamma characteristic of the image forming apparatus always ideal.

  The corrected CMYK gradation data corrected in this way is input to the halftoning unit 116. The halftoning unit 116 performs halftoning processing such as an error diffusion method, a dither method, and a screen method, and inputs halftone CMYK gradation data of 8 bits per pixel to the pulse modulation unit 117. The content of the halftoning process varies depending on the type of image to be formed. That is, based on a determination criterion such as whether the image is a monochrome image, a color image, a line image, or a graphic image, the optimum processing content for the image is selected and executed.

  The CMYK gradation data after halftoning input to the pulse modulation unit 117 is a multi-value signal indicating the size and arrangement of print dots of each color of CMYK to be attached to each pixel. The unit 117 uses the halftone CMYK gradation data to create a video signal for pulse width modulating the exposure laser pulses of the CMYK color images of the engine unit EG, and the engine controller via a video interface (not shown) 10 is output. Upon receiving this video signal, the laser driver 121 controls ON / OFF of the semiconductor laser of the exposure unit 6 to form an electrostatic latent image of each color component on the photosensitive member 22. In this way, image formation corresponding to the image signal is performed.

  Further, in this type of image forming apparatus, the gamma characteristic of the apparatus changes for each apparatus and also in the same apparatus depending on the use situation. Therefore, in order to eliminate the influence of the variation in gamma characteristics on the image quality, a gradation control process is executed to update the contents of the gradation correction table 118 based on the actual measurement result of the image density at a predetermined timing. To do.

  In this gradation control process, for each toner color, a gradation patch gradation image prepared in advance for measuring the gamma characteristic is formed on the intermediate transfer belt 71 by the engine unit EG, and each gradation patch is obtained. The density sensor 60 reads the image density of the image, and the gradation characteristic detecting unit 123 based on the signal from the density sensor 60 determines the gradation characteristic (corresponding to the gradation level of each gradation patch image and the detected image density). The gamma characteristics of the engine unit EG are created and output to the correction table calculation unit 119 of the main controller 11. Then, the correction table calculation unit 119 compensates the actually measured gradation characteristic of the engine unit EG based on the gradation characteristic given from the gradation characteristic detection unit 123 to obtain an ideal gradation characteristic. The tone correction table data is calculated, and the content of the tone correction table 118 is updated to the calculation result. Thus, the gradation correction table 118 is changed and set. By doing so, this image forming apparatus can form an image with stable quality regardless of variations in gamma characteristics of the apparatus and changes over time.

  The density control technique in this image forming apparatus will be described more specifically. In this apparatus, the image quality is stably maintained by performing density control processing described below at an appropriate timing, for example, immediately after the apparatus is turned on or when returning from sleep. In the density control process, the operating condition of the engine unit EG is optimized based on the density detection result of the patch image, and the above-described gradation control process is performed under the optimal operating condition.

  FIG. 4 is a flowchart showing density control processing in the image forming apparatus. In this process, first, the operating conditions of the engine unit EG are optimized. That is, a solid image as a patch image is formed on the intermediate transfer belt 71 with each bias value while changing and setting the developing bias applied to the developing roller 44 in multiple stages, and the solid image density is determined based on the density detection result. The optimum value of the developing bias to be the high density side target density is calculated (step S101). Subsequently, while the exposure power from the exposure unit 6 is changed and set in multiple stages under the optimum development bias thus obtained, for example, a 1 on 10 off line image is formed as a patch image with each exposure power, and the density detection is performed. Based on the result, an optimum value of exposure power at which the line image density becomes a predetermined low density side target density is calculated (step S102).

  In addition, as a process for optimizing the operating condition of the engine unit EG performed in this way, a known technique, for example, a technique described in Japanese Patent Application Laid-Open No. 2003-215862 can be applied. Is omitted.

  Subsequently, the gradation control process (steps S103 to S108) is executed under the operating conditions optimized as described above. Here, the principle of the gradation control process in this embodiment will be described first.

  FIG. 5 is a diagram for explaining the principle of gradation control processing in this embodiment. In this type of image forming apparatus, as the amount of toner that forms an image by adhering to the sheet S that is a recording medium increases, the image density increases approximately in proportion to this, but the amount of toner adhering to some extent is increased. As it becomes larger, the increase in image density becomes dull and eventually saturates and hardly changes. This is because when the surface of the sheet S is covered with toner, the image density in that portion is almost the color of the toner, and even if the amount of toner is increased further, the image density does not increase. In the following, in the characteristic between the toner adhesion amount and the image density (FIG. 5), a region where the image density is substantially proportional to the toner adhesion amount is referred to as a “proportional region”, and a region where the image density does not change so much is referred to as a “saturation region”. I will call it.

  Assume that the target density of the solid patch image (corresponding to the gradation value 255) is set to the value Dmax shown in FIG. 5 in step S101. This is an appropriate setting in that even if the toner adhesion amount varies slightly, the variation in the solid image density can be suppressed to a minimum. When an image having various gradation values is formed under operating conditions optimized with such settings, a gradation value equal to or lower than a certain gradation value Lmax (hereinafter referred to as “saturation start gradation value”) is obtained. In an image having a gradation value, the gradation value and the image density are substantially proportional. However, in an image having a gradation value equal to or greater than the saturation start gradation value Lmax, the change in image density becomes extremely small, and the one-to-one correspondence between the toner adhesion amount and the image density is lost. End up. This indicates that the toner adhesion amounts do not always match between two images having the same image density, which causes an increase in calculation error of the toner consumption amount.

  Therefore, in the gradation control processing of this embodiment, the change amount (0 to 255) of the gradation value (input gradation value) specified by the given image signal is a pair of the toner adhesion amount and the image density. The gradation correction table 118 is set so that the change width (0 to Lmax) corresponding to 1 is output. That is, in this embodiment, the image data output from the color conversion unit 114 is represented by gradation values from 0 to 255, but the image data output from the gradation correction unit 115 is from 0 to Lmax. Represented by value. That is, the gradation correction unit 115 performs scaling so that the gradation value of the output image data is equal to or less than the saturation start gradation value Lmax.

  By doing this, in addition to being able to form an image with good gradation reproducibility while maintaining a one-to-one relationship between the gradation value of the input image data and the image density, the gradation value Since the one-to-one relationship is also established between the toner amount and the toner adhesion amount, it is possible to improve the calculation accuracy of the toner consumption amount. As described above, by performing the gradation control process of this embodiment, it is possible to form an image while achieving both the image quality and the calculation accuracy of the toner consumption.

  The specific processing content of the gradation control processing will be described with reference to FIG. 4 again. First, a gradation patch image having an image pattern described below is formed on the intermediate transfer belt 71 (step S103).

  FIG. 6 shows a gradation patch image. The gradation patch image Igp formed on the intermediate transfer belt 71 is a belt-like image extending along the moving direction D2 of the intermediate transfer belt 71, and has a front end portion having a maximum gradation value (255) and a rear end. There is a gradation in which the gradation value gradually decreases toward the edge. Note that the image pattern of the gradation patch image is not limited to that shown in FIG. 6, and for example, the gradation value may be configured to change stepwise. Further, a gradation patch image in which image pieces having different gradation values are discretely formed may be formed.

  Returning to FIG. 4, the description of the gradation control process will be continued. The image density of the gradation patch image Igp formed in this way is detected by the density sensor 60 while changing the detection position in various ways (step S104). Specifically, the output from the density sensor 60 is sampled while the intermediate transfer belt 71 is moved around, and the sensor output at each position and the tone value of the patch image at that position are stored in association with each other. .

  Subsequently, a saturation start gradation value Lmax corresponding to the boundary between the proportional area and the saturation area shown in FIG. 5 is obtained. Here, based on the principle described below, the change rate of the image density with respect to the tone value is calculated from the density detection result of the previously obtained tone patch image Igp (step S105), and the density change rate is determined in advance. The gradation value when the threshold value Δth becomes the saturation start gradation value Lmax (step S106).

  FIG. 7 is a diagram for explaining how to obtain the saturation start gradation value. When the density detection result of the gradation patch image Igp is plotted against the gradation value, the patch image density increases as the gradation value increases in the low gradation value region, as shown by the broken line in the lower graph of FIG. However, the gradient gradually decreases in the high gradation value range and finally becomes substantially flat. When the density change rate at this time is plotted against the gradation value, as shown by the solid line in the lower graph of FIG. 7, the low gradation value area is almost flat, but the high gradation value area corresponds to the slowing of the image density increase. As a result, the rate of change in concentration rapidly decreases.

  The gradation value at which the density change rate rapidly decreases in this way corresponds to the saturation start gradation value Lmax that shifts from the proportional region to the saturated region in FIG. Therefore, a threshold value Δth whose density change rate with respect to the tone value is smaller than the flat end value is determined in advance, and the tone value when the density change rate decreases to this threshold value Δth is set as the saturation start tone value Lmax. That's fine.

  Returning to FIG. 4, the description of the gradation control process will be continued. When the saturation start gradation value Lmax is obtained in this way, the characteristics of the output gradation value with respect to the input gradation value (output gradation characteristics) so that the maximum value of the output gradation value becomes the saturation start gradation value Lmax by scaling. (Step S107), the contents of the gradation correction table 118 are updated based on the result, and the gradation correction process is terminated (step S108).

  FIG. 8 is a diagram illustrating an example of output gradation characteristics. If the gamma characteristic of the engine unit EG can be regarded as almost linear, the density detection result in the low gradation value range is almost linear as shown by the broken line in the lower graph of FIG. As shown by curve (a) in FIG. 8, the output gradation value of the gradation correction unit 115 has characteristics such that the input gradation value (0 to 255) is normalized by the saturation start gradation value Lmax. . On the other hand, if the gamma characteristic of the engine unit EG is wavy, a wave appears in the relationship between the gradation value and the density detection result in FIG. Therefore, the output from the gradation correction unit 115 has a characteristic that cancels this undulation, for example, a characteristic as shown by a curve (b) in FIG.

  As a result, the image data output from the color conversion unit 114 is processed by the gradation correction unit 115, whereby the maximum value is regulated to the saturation start gradation value Lmax and the gamma characteristic of the engine unit EG is canceled. Such characteristics are given and input to the halftoning unit 116. Thereby, in this embodiment, an image can be formed with good image quality without being affected by the gamma characteristic of the engine unit EG. Further, since a one-to-one relationship is maintained between the image data after color conversion and the toner adhesion amount, the toner consumption amount can be accurately obtained by using the toner counter 200 described below. .

  FIG. 9 is a diagram showing the configuration of the toner counter in this embodiment. The toner counter 200 receives image data color-converted corresponding to each toner color in the color conversion unit 114 of the main controller 11, and calculates toner consumption based on the image data. More specifically, the image data is input to the accumulator 203 via the data correction unit 202 with the correction table 201. The accumulator 203 integrates the gradation values of the data output from the data correction unit 202, and outputs an integrated value for one page of the image. In other words, the accumulator 203 counts the accumulated values after correcting the gradation values of the print dots constituting one page image.

  The correction table 201 and the data correction unit 202 are provided in consideration of a difference in toner consumption due to a difference in processing screen applied in the halftoning unit 116.

  FIG. 10 is a diagram showing the difference in gradation reproduction characteristics depending on the type of screen. The halftoning unit 116 performs screen processing on the image data output from the gradation correction unit 115. The type of screen applied in this case varies depending on the content of the image. That is, when the image to be formed is a photograph or an illustration, the halftone reproducibility is important. Therefore, as shown in the curve (a) of FIG. A screen (gradation priority screen) in which the relationship is substantially linear is applied in the halftoning unit 116. In this case, the toner consumption amount is approximately proportional to the input gradation value.

  On the other hand, in the case of an image composed of text and a chart, as shown in a curve (b) in FIG. 10, a screen (resolution priority screen) in which image contrast is enhanced with priority on resolution is applied. As a result, when the resolution priority screen shown in the curve (b) of FIG. 10 is applied, the toner consumption in the high gradation value range tends to increase. In FIG. 10, “100% gradation value” means not the maximum value 255 in 256 levels, but the maximum value Lmax regulated by the gradation correction unit 115.

  Thus, the tendency of toner consumption differs slightly depending on the type of screen applied. Therefore, in this embodiment, the tendency of toner consumption for each screen, that is, the characteristic curve shown in FIG. 10 is tabulated and stored in the correction table 202, and the image data is corrected according to the type of screen to be applied. While accumulating. That is, the image data input from the color conversion unit 114 to the data correction unit 202 is corrected with reference to the correction table 201 selected according to the type of screen, and the gradation value indicated by the corrected data is Accumulated by the accumulator 203. By doing so, it is possible to obtain the toner consumption more accurately in response to the difference in the toner consumption due to the difference in the screen. Note that when using a screen having a linear tone reproduction characteristic as shown by the curve (a) in FIG. 10, it is natural that the image data need not be corrected in calculating the toner consumption amount. .

  The accumulated value accumulated in the accumulator 203 for one page of image is multiplied by a predetermined coefficient K0 corresponding to the toner adhesion rate per gradation value. The result is a value corresponding to the toner consumption for one page of the image. A predetermined offset value Coff is added to this value.

  The offset value Coff is a value corresponding to the amount of toner consumed in a form that does not contribute to image formation corresponding to given image data. Such toner is separated from the developing roller 44 and adheres to the photosensitive member 22 to cause fogging or scatter inside the apparatus, or is consumed inside the apparatus in the control operation for maintaining the performance of the apparatus. Toner etc. This includes toner consumed for forming various patch images in this embodiment. Since the amount of toner consumed in this manner is correlated with the operation time of the apparatus, the number of images formed, the operation conditions of the apparatus, and the like, the toner in the period is based on these pieces of information managed by the engine controller 10. The consumption amount is estimated and set as an offset value Coff, and the sum of the toner consumption amount corresponding to the image data and the offset value is set as the toner consumption amount of the entire apparatus.

  The toner consumption thus obtained is managed by the CPU 101 provided in the engine controller 10 and stored in the RAM 107 or the memory 91 such as each developing device 4Y as necessary. Further, it is possible to estimate the toner remaining amount of each developing device from the obtained toner consumption value, and when it is determined that the toner remaining amount in the developing device has decreased to a predetermined value or less, the display unit 12 For example, a message prompting the developer to be replaced can be displayed, which can be useful for managing consumables of the apparatus.

  As described above, in this embodiment, data processing based on the relationship between the gradation value obtained from the density detection result of the gradation patch image Igp and the image density is performed on the image data after color conversion. An image corresponding to the subsequent image data is formed. In this data processing, the output gradation value is scaled so that the increase in image density with respect to the gradation value becomes equal to or less than the saturation start gradation value Lmax at which saturation begins. Further, data processing for adding a characteristic for compensating the gamma characteristic of the engine unit EG and an arbitrary gradation reproduction characteristic are added. Therefore, in this embodiment, it is possible to form an image with excellent image quality having excellent gradation reproducibility. In addition, since the density control process is performed at an appropriate timing, it is possible to stably form an image with good image quality.

  Further, since a one-to-one relationship is maintained between the color-converted image data and the toner adhesion amount, the toner consumption amount can be accurately obtained based on the relationship. As described above, according to this embodiment, it is possible to achieve both good image quality and accurate determination of toner consumption. In addition, although the image is formed with the same image density, it is possible to solve the problem that the way in which toner is apparently and actually reduced greatly depending on the state of the apparatus or between the two apparatuses.

  As described above, in this embodiment, the engine unit EG functions as the “image forming unit” of the present invention. Further, among the functional blocks of the main controller 11, the gradation correction unit 115 and the halftoning unit 116 function together as “data processing means” of the present invention. In this embodiment, the toner counter 200 functions as the “toner consumption calculation means” of the present invention. In this embodiment, the image data output from the color conversion unit 114 corresponds to the “input image data” of the present invention, and the image data after the data processing output from the halftoning unit 116 is the “input image data” of the present invention. This corresponds to “output image data”.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the main controller 11 is configured by combining independent functional blocks. However, data processing such as gradation correction processing and halftoning processing, particularly when each functional block is realized by software. May be processed integrally, and each functional block in the main controller 11 does not always have to be clearly distinguished as in the present embodiment.

  In the above embodiment, image formation and toner consumption calculation are performed based on image data after receiving RGB image data from the host computer and converting it to toner colors (CMYK). If only image data corresponding to the black color is transmitted, such as when the image data originally corresponds to the toner color is transmitted, the image formation and toner can be performed without performing color conversion. It can be used for consumption calculation.

  In each of the above embodiments, the toner consumption amount is obtained for each page of the image. However, the present invention is not limited to this. For example, the toner consumption amount is calculated for each job or for each block obtained by further dividing one page. You may make it ask.

  Further, the present invention is not limited to the configuration of the above-described embodiment. For example, an apparatus that includes only a developing device corresponding to black toner and forms a monochrome image, and an apparatus that includes a transfer medium (transfer drum, transfer sheet, etc.) other than the intermediate transfer belt. In addition, the present invention can be applied to other image forming apparatuses such as copying machines and facsimile machines.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. The figure which shows the signal processing block in this apparatus. 6 is a flowchart showing density control processing in the image forming apparatus. The figure for demonstrating the principle of the gradation control process in this embodiment. The figure which shows a gradation patch image. The figure for demonstrating how to obtain | require a saturation start gradation value. The figure which shows the example of an output gradation characteristic. FIG. 3 is a diagram showing a configuration of a toner counter in this embodiment. The figure which shows the difference in the gradation reproduction characteristic by the kind of screen.

Explanation of symbols

  115: gradation correction unit (data processing unit), 116: halftoning unit (data processing unit), 200: toner counter (toner consumption calculation unit), EG engine unit (image forming unit)

Claims (8)

In an image forming apparatus that forms an image using a built-in toner,
Data processing means for performing predetermined data processing on multi-tone input image data corresponding to a toner color to generate multi-tone output image data;
Image forming means for forming an image corresponding to the output image data;
Toner consumption calculation means for calculating the amount of toner consumed for image formation based on the input image data;
The data processing means performs the data processing so that a predetermined correlation is established between the input image data and the output image data, and the gradation value and the image obtained in advance in the image forming means are determined. The image formation is characterized in that the gradation value of the output image data is scaled so that the increase in the image density with respect to the increase in the gradation value is equal to or less than the saturation start gradation value based on the relationship with the density. apparatus.   The image forming apparatus according to claim 1, wherein the data processing unit generates the output image data having a gradation value proportional to a gradation value of the input image data.   The image forming apparatus according to claim 1, wherein the toner consumption amount calculating unit integrates gradation values of the input image data and calculates a toner consumption amount based on the integration value.   The image forming apparatus according to claim 1, wherein the data processing unit generates the output image data having a predetermined gradation reproduction characteristic with respect to a gradation value of the input image data.   The image formation according to claim 4, wherein the toner consumption amount calculating unit corrects and integrates the gradation value of the input image data based on the gradation reproduction characteristic, and calculates the toner consumption amount based on the integrated value. apparatus. The image forming unit forms a patch image with each gradation value while changing and setting gradation values in multiple stages,
The image forming apparatus according to claim 1, wherein the data processing unit determines the saturation start gradation value based on a density detection result of the patch image.   7. The image according to claim 6, wherein the data processing means sets the minimum value among the tone values at which the increase in the density of the patch image with respect to the increase in the tone value is a predetermined threshold value or less as the saturation start tone value. Forming equipment. A data processing step of performing data processing on multi-tone input image data corresponding to a toner color to generate multi-tone output image data having a predetermined correlation with the input image data;
An image forming step of forming an image corresponding to the output image data using toner;
A toner consumption calculation step for calculating an amount of toner consumed for image formation based on the input image data,
In the data processing step, based on the relationship between the gradation value and the image density obtained in advance in the image forming step, the increase in the image density with respect to the increase in the gradation value is equal to or less than the saturation start gradation value at which saturation starts. An image forming method characterized by scaling gradation values of the output image data.

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