Patent Publication Number: US-2006007509-A1

Title: Image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION(S)  
      This application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2004-199647, filed on Jul. 6, 2004, the entire contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of Invention  
      The present invention relates to image forming apparatuses such as copy machines, laser beam printers, facsimile apparatuses, and the like using an electrophotographic method wherein image processing and correction processing of image information is digitally performed.  
      2. Related Art  
      Generally, with image processing in electrophotographic apparatuses such as digital copy machines, a digital image signal input by an image input apparatus such as a scanner is output as an output image signal after such digital signal processing as input signal processing, region separation processing, color correction processing, black generation processing, zoom variable power processing, and the like, then performing filter processing with a spatial filter, and also performing halftone correction processing.  
       FIG. 5  shows a control block diagram of image processing for a conventional digital copy machine. This conventional digital copy machine includes an input signal processing portion  110 , a region separation processing portion  120 , a color correction/black generation processing portion  130 , a zoom variable power processing portion  140 , a spatial filter processing portion  150 , a halftone correction processing portion  160 , a pixel counting portion  170 , and a toner consumption calculating portion  180 .  
      The image processing in this sort of digital copy machine is explained with reference to  FIG. 6 .  
      First, the digitally input image signal of the manuscript read into a scanner or the like is input into the input signal processing portion  110 , and preprocessing for the subsequent image processing, input gamma correction by image adjustment, and conversion are performed (Step S 101 , S 102 ).  
      Next, this image signal is input into the region separation processing portion  120 , regions such as text regions and halftone dot photograph regions are judged, and an identification signal showing the judgment of those regions (a region separation identification signal) is added (Step S 103 ). This region separation identification signal is used when, in the spatial filter processing portion  150  and the halftone correction processing portion  160  that are used for subsequent processing, performing processing differing for each region, for example, performing smoothing filter processing for halftone regions or performing edge emphasis filter processing for text regions, or when changing the halftone gamma properties to properties with clearer grayscale difference properties.  
      The color correction/black generation processing performed in the following color correction/black generation processing portion  130  (Step S 104 ) is a necessary process when the apparatus is a color apparatus, and this processing converts the RGB image signal sent from the region separation processing portion  120  to a CMYK (yellow, magenta, cyan, black) image signal, which is the final output method.  
      After the variable power processing in the zoom variable power processing portion  140  (Step S 105 ), the image signal converted to CMYK is input to the spatial filter processing portion  150 . In the spatial filter processing portion  150 , a spatial filter is chosen from the spatial filter table in accordance with the region separation identification signal and the image mode setting state, and spatial filter processing is performed on the image signal converted to CMYK (Step S 106 ). The spatial filter table is a table group of filter coefficients referred to when performing the spatial filter processing, wherein it is possible to select a desired table according to the circumstances.  
      Correction of the halftone gamma properties is performed (Step S 107 ) in the next halftone correction processing portion  160 , in order to correct the output properties at an engine portion.  
      Further, the image signal after halftone correction processing is input to the pixel counting portion  170 , and is summed by the counter while weighting each CMYK signal in pixel units (Step S 108 ). Then, the output image signal flows to the LSU or LED engine output (Step S 110 ). In the toner consumption calculating portion  180 , the toner consumption for each color is calculated from the pixel count sum value summed in the pixel counting portion  170  (Step S 109 ). The calculated toner consumption is used for accumulation of toner consumption data and determining when the toner is near the end of its life.  
      The engine of the type of digital copy machine described above is controlled such that a constant toner density and image output is output from the beginning until the end of toner life, by controlling the setting of process conditions such as developing bias values and the amount of exposure and toner density correction, in order to suppress aging of photosensitive bodies, developer, and the like.  
       FIG. 7  is a flow chart showing a simplified view of the toner density control processing, which is a control performed on the engine side. With this toner density control processing, the control value of the toner density sensor is determined from the values of the life counter and environment sensor (Step S 111 , S 112 ), and ON/OFF of the toner refilling is controlled according to that value. That is, when the toner density is low (when judged YES in Step S 113 ), the toner refill is turned ON, and controlled such that toner is refilled (Step S 114 ). Thereby, the toner density is controlled such it is always kept constant.  
       FIG. 8  is a flow chart showing a simplified view of the halftone gamma correction processing by the toner patch. With this halftone gamma correction processing, a toner patch is formed on a photosensitive body or a transfer belt (Step S 121  to S 123 ) with a halftone pattern (tone) according to a predetermined fixed input level, and the reflected light quantity of the toner patch is read by a reading device such as an optical sensor (Step S 124 ). Next, the sensor output level of the read toner patch is compared to the standard target level which is the target level, and the amount of correction is calculated (Step S 125 ). Then, according to that calculated amount of correction, the current halftone gamma correction table is revised (Step S 126 ), and thereby, controlled such that constant halftone gamma properties are always obtained.  
      Next, the calculation of the toner consumption noted above will be described in detail. The processing stated below is performed with respect to each CMYK color (each input CMYK signal).  
      The pixel counting portion  170  performs a pixel count as described below for the input multi-level image. As shown in  FIG. 5 , the pixel counting portion  170  is provided with a counting means  171 , a weighting calculation means  172 , a weighting coefficient table  173 , and a summing means  174 .  
      The counting means  171  counts each pixel of the input multi-level image (for example, multi-grade images such as 16-grade and 256-grade images). That is, input signals such as the input level (grade) of each pixel constituting a multi-level image, for example 0 to 15 (in the case of a 16-grade image wherein the input signal takes on the levels 0 to 15) are counted.  
      The weighting calculation means  172  performs weighting of each pixel when counting the pixels with the counting means  171 . Specifically, the weighting calculation means  172  obtains a weighting coefficient corresponding to the input signal level of each pixel from the weighting coefficient table  173 , and multiplies the obtained weighting coefficients by the input signal levels. Weighting coefficients corresponding to each pixel input level when weighting is performed by the weighting calculation means  172  are stored in the weighting coefficient table  173 . In this way, in the pixel counting portion  170 , a pixel count is performed for each pixel by the counting means  171 , the weighting calculation means  172 , and the weighting coefficient table  173 .  
      Summation of the pixel count performed for each pixel is performed by the summing means  174 . That is, the summing means  174  sums the calculated value for each pixel wherein a weighting coefficient has been multiplied by the input signal level by the weighting calculation means  172 , over all pixels of the input multi-level image. In this way, based on the sum value of the pixel count calculated by the pixel counting portion  170 , the toner consumption calculating portion  180  calculates the toner consumption of the output image.  
      The weighting coefficient stored in the weighting coefficient table  173  is a fixed value set in advance. An example of the weighting coefficient table  173  when the input signal takes 16 levels from 0 to 15 is shown in the following Table 1.  
      Conventional Art  
               TABLE 1                          Weighting Coefficient Table (Fixed)                             Signal   Weighting           input level   coefficient                                             Area 1   0 to 4   0           Area 2   5 to 8   1           Area 3   9 to 12   3           Area 4   13 to 15   4                      
 
      Table 1 is divided into four areas (area  1  to area  4 ) corresponding to the different input signal levels of toner consumption, and a weighting coefficient is set for each area. When counting pixels, the weighting coefficient, which is divided into the four areas, is set corresponding to the respective input signal levels that take on the levels 0 to 15.  
       FIG. 9  shows the relationship between signal input levels of the weighting coefficient table divided into the four areas shown in Table 1 and the corresponding weighting coefficients. As shown in  FIG. 9 , the total area of the rectangular portions roughly matches the area of the curve showing the toner consumption properties, and therefore it is possible to predictably calculate the toner consumption from the pixel count sum value after weighting.  
      Image forming apparatuses have been proposed wherein toner thin layer nonuniformities are efficiently prevented when successively printing images which have an extremely small toner consumption rate (for example, JP 2002-287499A). Particularly, image forming apparatuses have been disclosed that have a pixel counter, a recording page counter, and a toner consumption means, wherein when a number of pixels below a predetermined level have been counted during a predetermined number of recording pages, during process control, along with performing a judgment that a consumption action is executed by the toner consumption means, the toner consumption means is created at the same time as creation of the process control toner patch when executing the consumption action.  
      However, in conventional electrophotographic apparatuses such as digital copy machines, there were the following problems.  
      As stated above, when performing the pixel count and calculating the toner consumption of the output image, a weighting coefficient table was used in which was stored a fixed weighting coefficient set in advance. Incidentally, when using this sort of weighting coefficient table, as shown in  FIG. 9 , the weighting coefficient determined from the weighting coefficient table for a particular input signal level may differ greatly from the value on the curve that shows the toner consumption properties for that input signal level. Therefore, there is the problem that the toner consumption cannot be accurately calculated from the sum value of the pixel count after weighting.  
      In this case, for example, as shown in  FIG. 10 , a method is conceivable wherein the difference between the actual toner consumption properties and the toner properties calculated by the pixel count is decreased by using a weighting coefficient table in which the levels that can be taken from the input signal levels, that is, the weighted coefficients of the tone numbers of the input signal, are apportioned. However, when the toner consumption properties change from curve D shown by the solid line in  FIG. 10  to the broken line shown by curve E due to individual differences or toner life, it is not possible to follow the change in the toner properties by simply raising the number of gradations of the weighting coefficient table, the difference between the actual toner consumption properties and the toner properties calculated by the pixel count cannot be reduced, and toner consumption cannot be accurately calculated.  
     SUMMARY OF THE INVENTION  
      The present invention was made in light of the problems in the conventional technology mentioned above, and it is an object thereof to provide an image forming apparatus that can accurately calculate toner consumption irregardless of individual differences and toner life.  
      The present invention is configured in the following manner as a means for solving the problems mentioned above. That is, according to the present invention, an image forming apparatus that digitally performs image processing and correction processing of the image information and calculates toner consumption by performing a pixel count of the input multi-level image comprises: a counting portion (counting means) that counts, pixel by pixel, input signal levels of the input multi-level image; a weighting coefficient table that stores weighting coefficients corresponding to the input signal for the input signal levels of the input multi-level image; and a weighting calculation portion (weighting calculation means) that obtains from the weighting coefficient table weighting coefficients corresponding to the input signal levels and performs weighting of each pixel when the input signal levels are counted by the counting portion; wherein the weighting coefficients stored in the weighting coefficient table are adjustable.  
      With the image forming apparatus configured in this manner, even when actual toner consumption properties have changed due to individual differences or toner life, by changing the weighting coefficients stored in the weighting coefficient table according to this change in toner consumption properties, it is possible to optimize the calculation of toner consumption properties. As a result, it is possible to accurately calculate toner consumption regardless of individual differences and toner life.  
      Also, according to the present invention, an image forming apparatus that digitally performs image processing and correction processing of the image information and calculates toner consumption by performing a pixel count of the input multi-level image may comprise: a counting portion (counting means) that counts, pixel by pixel, the input signal levels of the input multi-level image; a weighting coefficient table that stores weighting coefficients corresponding to the input signal; a weighting calculation portion (weighting calculation means) that obtains from the weighting coefficient table weighting coefficients corresponding to the input signal levels and performs weighting of each pixel when the input signal levels are counted by the counting portion; and a rewriting portion (rewriting means) that rewrites the weighting coefficients stored in the weighting coefficient table.  
      More specifically, the present invention may also be configured such that a reading portion that reads a toner patch is further provided, the above rewriting portion forms a plurality of toner patches on a photosensitive body or transfer belt with mutually differing tones, these multiple toner patches are read by the reading portion (reading means), and based on the result of reading these toner patches the halftone gamma properties are calculated, and according to these calculated halftone gamma properties the weighting coefficients stored in the weighting coefficient table are rewritten.  
      With an image forming apparatus having this sort of configuration, even when actual toner consumption properties have changed due to individual differences and toner life, it is possible to rewrite the weighting coefficient of a weighting coefficient table so that it follows this change in toner consumption properties, and the calculation of toner consumption properties can be optimized. As a result, it is possible to accurately calculate toner consumption regardless of individual differences and toner life. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a control block diagram showing the image processing in the image forming apparatus associated with an embodiment of the present invention.  
       FIG. 2  is a flow chart showing the processing of the toner consumption calculation for a single pixel.  
       FIG. 3  is a diagram showing the rewrite aspect of the weighting coefficient table.  
       FIG. 4  is a flow chart showing the rewrite processing of the weighting coefficient table.  
       FIG. 5  is a control block diagram showing the image processing in an image forming apparatus according to the conventional technology.  
       FIG. 6  is a flow chart showing the image processing in an image forming apparatus according to the conventional technology.  
       FIG. 7  is a flow chart showing a simplified view of the toner density control processing of the conventional technology.  
       FIG. 8  is a flow chart showing a simplified view of the halftone gamma correction processing by toner patch of the conventional technology.  
       FIG. 9  is a diagram showing the relationship between the signal input level and the corresponding weighting coefficients of the weighting coefficient table according to the conventional technology.  
       FIG. 10  is another diagram showing the relationship between the signal input level and the corresponding weighting coefficients of the weighting coefficient table according to the conventional technology. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Below follows a description of an embodiment of the present invention, with reference to the accompanying drawings. The embodiment described below is one specific example of the present invention, and does not limit the technical scope of the present invention.  
       FIG. 1  is a control block diagram showing the image processing in the image forming apparatus (digital electrophotographic apparatus) associated with an embodiment of the present invention. As shown in  FIG. 1 , this digital electrophotographic apparatus includes an input signal processing portion  10 , a region separation processing portion  20 , a color correction/black generation processing portion  30 , a zoom variable power processing portion  40 , a spatial filter processing portion  50 , a halftone correction processing portion  60 , a pixel counting portion  70 , and a toner consumption calculating portion (toner consumption calculating means)  80 . In the digital electrophotographic apparatus, a digitally input image signal of a manuscript imported by scanner or the like, not shown in the drawings, passes through the input signal processing portion  10 , the region separation processing portion  20 , the color correction/black generation processing portion  30 , the zoom variable power processing portion  40 , the spatial filter processing portion  50 , and the halftone correction processing portion  60 , and is output as an output image signal. Further, a reading means  90  such as an optical sensor or the like is provided in order to read the reflected light quantity of a toner patch (details given below).  
      The image processing in the digital electrophotographic apparatus configured in this manner will now be explained.  
      In the input signal processing portion  10 , preprocessing for subsequent image processing, input gamma correction processing and conversion in image adjustment are performed on the digitally input image signal of a manuscript imported by scanner or the like not shown in the drawings.  
      In the region separation processing portion  20 , regions such as text regions and halftone dot photograph regions are judged, and an identification signal showing the judgement of those regions (a region separation identification signal) is added. This region separation identification signal is used when, in the spatial filter processing portion  50  and the halftone correction processing portion  60  that are used for subsequent processing, performing processing differing for each region, for example, performing smoothing filter processing for halftone regions or performing edge emphasis filter processing for text regions, or when changing the halftone gamma properties to properties with clearer grayscale difference properties.  
      In the color correction/black generation processing portion  30 , the RGB image signal sent from the region separation processing portion  20  is converted to a CMYK (yellow, magenta, cyan, black) image signal, which is the final output method. In the zoom variable power processing portion  40 , variable power processing is performed on the CMYK image signal converted by the color correction/black generation processing portion  30 .  
      In the spatial filter processing portion  50 , a spatial filter is selected from the spatial filter table according to the previously mentioned region separation identification signal and the image mode setting state, and spatial filter processing is performed on the image signal converted to CMYK. In the halftone correction processing portion  60 , a correction of the halftone gamma properties is performed on the image signal on which spatial filter processing was performed. Then, the image signal after halftone correction processing in the halftone correction processing portion  60  is output as an output image signal.  
      In the pixel counting portion  70 , a pixel count is performed for the image signal after halftone correction processing with the halftone correction processing portion  60 , while multiplying a weighting coefficient by each CMYK signal in pixel units. In the toner consumption calculating portion  80 , toner consumption is calculated for each color (CMYK) from the sum value of the pixel count.  
      Below, the toner consumption calculation process in the digital electrophotographic apparatus is explained in detail. The process referred to below is performed for each CMYK color (each input CMYK signal).  
      The pixel counting portion  70  performs a pixel count as described below for the input multi-level image. As shown in  FIG. 1 , the pixel counting portion  70  is provided with a counting means  71 , a weighting calculation means  72 , a weighting coefficient table  73 , a summing means  74 , and a rewriting means  75 .  
      The counting means  71  counts each pixel of the input multi-level image (for example, 16-grade and 256-grade multi-level images). That is, it counts the input signal (grade) of each pixel constituting the multi-level image, for example, it counts an input signal level such as 0 to 15 (in the case of a 16-grade image, wherein the input signal level takes on the levels 0 to 15).  
      The weighting calculation means  72  performs weighting of each pixel when the pixels are counted by the counting means  71 . Particularly, the weighting calculation means  72  obtains a weighting coefficient corresponding to the input signal level of each pixel from the weighting coefficient table  73 , and multiplies the obtained weighting coefficient by the input signal levels. The weighting coefficients corresponding to each pixel input level when weighting is performed by the weighting calculation means  72  are stored in the weighting coefficient table  73 . In this way, in the pixel counting portion  70 , a pixel count of each pixel is performed by the counting means  71 , the weighting calculation means  72 , and the weighting coefficient table  73 .  
      Then, summation of the pixel count performed for each pixel is performed by the summing means  74 . That is, the summing means  74  sums the calculation value of each pixel having a weighting coefficient multiplied by the input signal level by the weighting calculation means  72 , for every input pixel of the multi-level image. A rewriting means  75 , as explained below, rewrites the weighting coefficient table  73 . The toner consumption calculating portion  80  calculates the toner consumption of the output image, based on the sum value of the pixel count calculated by the pixel counting portion  70  (summed by the summing means  74 ).  
      The toner consumption calculation for a single pixel is explained using  FIG. 2 . As shown in  FIG. 2 , when the signal for a single pixel that is part of the multi-level image is input into the pixel counting portion  70  (Step S 11 ), the input signal level is counted by the counting means  71 . Next, a weighting coefficient corresponding to the input signal level is obtained by the weighting calculation means  72  from the weighting coefficient table  73  (Step S 12 ), and the obtained weighting coefficient is multiplied by the input signal level (Step S 13 ). Based on the pixel count for a single pixel calculated in this way, the toner consumption for that single pixel is calculated by the toner consumption calculating portion  80 . In step S 13 , the pixel count values calculated for each single pixel are sequentially summed by the summing means  74 , and saved as a pixel count sum value (Step S 14 ). The pixel count sum value is a pixel count value for all of the input pixels, and based on this pixel count sum value, the toner consumption of the output image is calculated by the toner consumption calculating portion  80 .  
      The rewriting of the weighting coefficient table  73  is explained using  FIG. 3  and  FIG. 4 . The weighting coefficients stored in the weighting coefficient table  73  are adjustable, unlike in the conventional technology, and can be rewritten by the rewriting means  75 . One example of the weighting coefficient table  73 , for the case of a 16-level input signal level that takes on input signal levels 0 to 15, is shown in the following Table 2.  
               TABLE 2                          Weighting Coefficient Table (Adjustable)                     Signal   Weighting       input level   coefficient                             0   X0       1   X1       2   X2       3   X3       4   X4       5   X5       6   X6       7   X7       8   X8       9   X9       10   X10       11   X11       12   X12       13   X13       14   X14       15   X15                  
 
      In Table 2, the weighting coefficients (X0 to X15) corresponding to the input signal levels 0 to 15 are each adjustable. The weighting coefficients X0 to X15 are rewritten as follows by the rewriting means  75 .  
      First, after the toner density has been corrected (Step S 21 ), a plurality of toner patches having mutually differing tones, as shown by points P 1  to P 3  in  FIG. 3 , are formed of the photosensitive body or transfer belt (Step S 22 ). That is, halftone toner patches for a plurality of input points set in advance are formed on the photosensitive body or transfer belt. Then, the amount of reflected light of those toner patches is read by a reading means  90  (see  FIG. 1 ) such as an optical sensor (Step S 23 ). In  FIG. 3 , the vertical axis is the sensor output of the reading means  90  such as an optical sensor, and the horizontal axis is the signal output level (grade). There is no particular limitation to the number of input points, but it is preferable to have at least three points. The procedure of the above steps S 21  to S 23  is similar to the steps S 122  to S 124  in the halftone gamma correction process shown in  FIG. 8 , stated above in the section explaining the conventional technology, and so the following procedure may also be performed, using the results of this halftone gamma correction process.  
      Next, based on the sensor output of toner patches for a plurality of input points, the halftone gamma properties as shown by the broken line in  FIG. 3  are calculated (Step S 24 ). Based on the calculated halftone gamma properties, the toner consumption properties for the signal input levels as shown by the solid line in  FIG. 3  are calculated (Step S 25 ). Based on the toner consumption properties calculated in this manner, the weighting coefficients are determined, and the weighting coefficients stored in the weighting coefficient table  73  are rewritten to the determined weighting (Step S 26 ). In the case of Table 2, the weighting coefficients X0 to X15 corresponding to the input signal levels 0 to 15 are rewritten according to the toner consumption properties.  
      In this way, a pixel count of the input multi-level image is performed by the pixel counting portion  70  using the weighting coefficient rewritten by the rewriting means  75 , and the toner consumption of the output image is calculated by the toner consumption calculating portion  80 .  
      In this way, even when actual toner consumption properties have changed due to individual differences and toner life, it is possible to follow the changes in toner consumption properties and rewrite the weighting coefficient table  73 , and the calculation of toner consumption properties can be optimized. The result of this is that toner properties can be accurately calculated irrespective of individual differences or toner life. That is, it is possible to hold the discrepancy between the actual toner consumption and the toner consumption calculated using the weighting coefficient table  73  rewritten by the rewriting means  75  to a low level.  
      The present invention can be embodied and practiced in other different forms without departing from the spirit and essential characteristics thereof. Therefore, the above-described embodiments are considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description. All variations and modifications falling within the equivalency range of the appended claims are intended to be embraced therein.