Image forming apparatus and method for controlling the same, and program

Abstract

To prevent a reduction in the accuracy of predicting the consumption of developer (toner) when dither processing is performed on an input image in an image forming apparatus.SOLUTION: An image signal generation unit 100 generates an image signal (VDO signal 110) by performing dither processing on an input image as halftone processing. A control unit 200 acquires (predicts) the consumption of developer for forming a developer image on the basis of the image signal. The control unit 200 acquires the consumption of developer by using a count value (OFF continuous count value) obtained by individually counting OFF pixel groups that are included in an image corresponding to the image signal and comprise continuous OFF pixels, and that have different continuous numbers, and the size of a dither matrix used in the dither processing.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that forms an image by an electrophotographic method, a control method thereof, and a program.

Background Art

[0002] In electrophotographic image forming apparatuses such as printers, copiers, and facsimile machines that form an image using a developer (toner), it is required to grasp the toner consumption amount (or remaining amount) in order to replenish the toner or replace the toner cartridge. For example, in the technique described in Patent Document 1, the printed dot sequence is classified into a plurality of patterns according to the continuous state of the dots, and the occurrence frequencies thereof are individually counted. Further, the total toner consumption amount is calculated by multiplying each of these count values by a predetermined coefficient and adding them. Thereby, the toner consumption amount is obtained with high accuracy regardless of the non-linearity between the number of dots and the toner adhesion amount due to the difference in the continuous state of the dots.

[0003] Also, in the technique described in Patent Document 2, the accuracy of calculating the toner consumption amount is improved by using the interval between other dots adjacent to the dots. In this technique, the amount of toner adhering to an area where toner adhesion is not planned, which is formed between toner dots, is predicted based on the dot interval.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above prior art, depending on the dot interval, the amount of toner adhering to areas where toner adhesion is not planned is different, and this is utilized to improve the accuracy of calculating the toner consumption. However, when performing dithering as a halftone process on an input image, the prediction accuracy in predicting the toner consumption using the formed dot intervals may decrease. This is because, for example, when the area ratio of the image after dithering is small, the reduction in toner consumption due to the formed dots becoming smaller is not reflected in the prediction of the toner consumption.

[0006] Therefore, an object of the present invention is to provide a technique for preventing a decrease in the prediction accuracy of the consumption amount of a developer (toner) when performing dithering on an input image.

Means for Solving the Problems

[0007] An image forming apparatus according to an aspect of the present invention includes a photoreceptor, a processing unit that generates an image signal by performing dithering as a halftone process on an input image, an exposure unit that forms an electrostatic latent image on the photoreceptor by exposing the photoreceptor based on the image signal, a developing unit that forms a developer image on the photoreceptor by developing the electrostatic latent image using a developer, and an acquisition unit that acquires the consumption amount of the developer for forming the developer image based on the image signal. The acquisition unit uses a count value obtained by individually counting OFF pixel groups composed of consecutive OFF pixels included in the image corresponding to the image signal and different consecutive numbers of OFF pixel groups, and the size of the dither matrix used for the dithering process to acquire the consumption amount.

Effects of the Invention

[0008] According to the present invention, when performing dithering on an input image, it is possible to prevent a decrease in the prediction accuracy of the consumption amount of a developer (toner).

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0011] [First Embodiment] As an example of an image forming apparatus according to an embodiment of the present disclosure, an electrophotographic laser beam printer (LBP) will be described. However, the image forming apparatus is not limited to only an LBP, and may be other types of image forming apparatuses such as a copying machine, a facsimile apparatus, and the like.

[0012] [Configuration of Image Forming Apparatus] FIG. 1 is a cross-sectional view showing a schematic hardware configuration example of an image forming apparatus 9 according to the first embodiment. The image forming apparatus 9 includes an image signal generation unit 100, a control unit 200, and an optical scanning unit 400. The optical scanning unit 400 includes a laser driving unit 300. The laser driving unit 300 in the optical scanning unit 400 outputs a laser beam (optical beam) 408 based on an image signal output from the image signal generation unit 100 and a control signal output from the control unit 200. Note that the image forming apparatus 9 is configured to form a monochromatic image using a monochromatic developer such as black developer (toner), but may be configured to form a multicolor image using, for example, yellow, magenta, cyan, and black developers.

[0013] The image forming apparatus 9 includes an image forming unit configured by an optical scanning unit 400, a photosensitive drum 4 (photoconductor), a charger 2, a developing device 3, and the like. In an image forming process started by the control unit 200, the charger 2 charges the photosensitive drum 4. The optical scanning unit 400 scans the surface (scanned surface) of the photosensitive drum 4 with a laser beam based on an image signal (image data) to form an electrostatic latent image on the surface of the photosensitive drum 4. The developing device 3 develops the electrostatic latent image formed on the photosensitive drum 4 (attaches toner to the electrostatic latent image) to form a toner image (developer image) on the photosensitive drum 4. In the present embodiment, the optical scanning unit 400 is an example of exposure means for forming an electrostatic latent image on the photosensitive member by exposing the photosensitive member based on an image signal. Further, the developing device 3 is an example of developing means for forming a developer image on the photosensitive member by developing an electrostatic latent image using a developer (toner).

[0014] The toner image formed on the photosensitive drum 4 is conveyed to the transfer position where it is transferred to a recording medium such as a sheet as the photosensitive drum 4 rotates. In accordance with the conveyance timing of the toner image to the transfer position, the recording medium is conveyed from the paper feed unit 8. The toner image formed on the photosensitive drum 4 is transferred onto the recording medium that is fed and conveyed from the paper feed unit 8 and whose skew is corrected by the registration roller 5. The recording medium onto which the toner image has been transferred is conveyed to the fixing device 6. The fixing device 6 performs a fixing process for fixing the toner image onto the recording medium. The recording medium on which the fixing process has been performed is discharged to the outside of the image forming apparatus 9 (discharge tray) by the discharge roller 7.

[0015] <Configuration of Image Signal Generation Unit, Control Unit, and Laser Driving Unit> FIG. 2 is a block diagram showing a configuration example related to the processing of an image signal in the image forming apparatus 9 according to the present embodiment. The image signal generation unit 100 receives print data from an external device (not shown) such as a host computer, and generates a VDO signal 110 (image signal) based on the received print data. The image signal generation unit 100 includes an image modulation unit 101 and a CPU 102. The VDO signal 110 output from the image signal generation unit 100 is input to the laser driving unit 300 and also input to the control unit 200 (pixel count unit 202 in the control unit 200).

[0016] The control unit 200 includes a CPU 201 and a pixel count unit 202. The CPU 201 controls the image forming apparatus 9. The pixel count unit 202 performs a counting process related to the presence or absence of pixels included in the VDO signal 110 (image signal) with reference to the input VDO signal 110. In the present embodiment, the CPU 201 is configured to acquire (predict) the consumption amount of the developer (toner) by the developing device 3 based on the VDO signal 110 (image signal). The CPU 201 uses the count value output from the pixel count unit 202 in acquiring the toner consumption amount.

[0017] The laser driving unit 300 includes a laser driver IC 301 and a laser 302. The laser 302 is composed of a semiconductor laser and is used as the light source of the laser driving unit 300. The laser driver IC 301 performs emission control (lighting and extinguishing) of the laser 302 based on the laser control signal 312 output from the control unit 200 and the VDO signal 110 output from the image signal generation unit 100. The laser driver IC 301 forms an electrostatic latent image corresponding to the VDO signal 110 on the photosensitive drum 4 by irradiating the scanned surface of the pre-charged photosensitive drum 4 with the laser light output from the laser 302.

[0018] <Pixel count unit> FIG. 3 is a block diagram showing an internal configuration example of the pixel count unit 202. The pixel count unit 202 includes a sample timing generation unit 221, a mask generation unit 222, a pixel counter 223, a sample number counter 224, a CPU communication unit 225, and a continuous counter 226.

[0019] The CPU communication unit 225 communicates with the CPU 201 via the CPU bus 211. The CPU communication unit 225 transmits each count value output from the sample number counter 224, the pixel counter 223, and the continuous counter 226 to the CPU 201. Also, the CPU communication unit 225 transmits various setting values received from the CPU 201 to the sample timing generation unit 221 and the mask generation unit 222. The various setting values include an image mask setting 232 transmitted to the mask generation unit 222. The image mask setting 232 includes information indicating the start and end timings of the sub-scan mask based on the TOP signal 112 and information indicating the start and end timings of the main scan mask based on the BD signal 111. In the present embodiment, the count process executed by the pixel count unit 202 is executed within the image area excluding the areas corresponding to the above-described sub-scan mask and main scan mask. Note that the BD signal 111 and the TOP signal 112 are generated by the CPU 201 and supplied to the image modulation unit 101 and the pixel count unit 202.

[0020] The sample timing generation unit 221 (clock signal generation unit) generates and outputs a sample timing signal (sampling clock signal) 234 that is transmitted to the pixel counter 223, the sample number counter 224, and the continuous counter 226. The sample timing signal 234 is output at a constant period. In this embodiment, it is assumed that the sample timing period of the pixel is set to 50 MHz, and the image clock period for forming one pixel is also set to 50 MHz. That is, one pixel sample timing occurs per pixel.

[0021] The mask generation unit 222 uses the TOP signal 112 and the BD signal 111 as references, and sets the mask signal 233 to the "LOW" level in the region (image region) where the image is formed (drawn) according to the image mask setting 232. The sample timing signal 234 is supplied as the sample timing signal 235 within the image region to the pixel counter 223, the sample number counter 224, and the continuous counter 226 during the period when the mask signal 233 is set to the "LOW" level (i.e., during the drawing of the image).

[0022] The pixel counter 223 has a counter for counting the valid pixels (ON pixels which are the pixels where toner adhesion is planned) of the VDO signal 110, and outputs a pixel count value 236 obtained by counting the ON pixels. When the pixel counter 223 receives the TOP signal 112 (sub-scanning synchronization signal), it clears the held pixel count value 236 to 0. The pixel counter 223 increments the pixel count value 236 by +1 when the sample timing signal 235 indicating the sample timing of the pixels within the image region is at the "HIGH" level and the VDO signal 110 is at the "HIGH" level. That is, the pixel counter 223 uses the sample timing signal 235 as a synchronization signal to count the "HIGH" level VDO signal 110 (i.e., count the ON pixels).

[0023] The sample number counter 224 has a counter for counting the number of receptions of the sample timing signal 235 in the image area. The sample number counter 224 outputs a sample number count value 237 obtained by counting the number of receptions of the sample timing signal 235 (a signal at the "HIGH" level) in the image area. When the sample number counter 224 receives the TOP signal 112 (sub-scanning synchronization signal), it clears the held sample number count value 237 to 0. The sample number counter 224 increments the sample number count value 237 by +1 when the sample timing signal 235 indicating the sample timing of the pixels in the image area is at the "HIGH" level.

[0024] <Continuous counter> Based on the input sample timing signal 235, the continuous counter 226 increments the continuous count value 238 by +1 when continuously counting pixels for the VDO signal 110 by a preset number of consecutive counts (discrimination consecutive number) to be discriminated. For example, when the discrimination consecutive number is set to 5, the continuous counter 226 increments the continuous count value 238 by +1 when the pixel counting continues for 5 consecutive times.

[0025] The continuous counter 226 is configured to be able to perform a continuous "HIGH" level count (i.e., count ON pixels) and a continuous "LOW" level count (i.e., count OFF pixels) in the VDO signal 110. The continuous counter 226 outputs an ON continuous count value obtained by counting the continuous "HIGH" levels in the VDO signal 110 for a preset number of consecutive counts (discrimination consecutive number) to be discriminated. Also, the continuous counter 226 outputs an ON continuous count value obtained by counting the continuous "LOW" levels in the VDO signal 110 for the discrimination consecutive number. In this embodiment, since the counting process by the continuous counter 226 is performed for the VDO signal 110, the counting of consecutive pixels (ON pixels or OFF pixels) in the main scanning direction is performed.

[0026] In this embodiment, the continuous counter 226 is a group of OFF pixels consisting of consecutive OFF pixels included in the image corresponding to the VDO signal 110 (image signal), and is configured to output a count value (OFF continuous count value) obtained by individually counting groups of OFF pixels having different consecutive numbers. Further, the continuous counter 226 may be further configured to output a count value (ON continuous count value) obtained by individually counting groups of ON pixels consisting of consecutive ON pixels included in the image corresponding to the VDO signal 110 (image signal).

[0027] <Dithering process> In the image forming apparatus 9 of this embodiment, the image signal generation unit 100 is configured to generate the VDO signal 110 (image signal) by performing halftone processing (dithering process) by the dither method on the input image. The image information of the input image is composed of, for example, pixel values (gray levels) of 8 bits for each pixel. By the dithering process, tone correction of the input image is performed. The tone correction is performed to correct the gamma characteristic according to the state of the image forming apparatus 9 and form a good halftone in the output image.

[0028] The image signal on which the dithering process has been performed by the CPU 102 is modulated into the VDO signal 110 by the image modulation unit 101. The VDO signal 110 generated by the image modulation unit 101 is supplied to the laser driving unit 300 and the control unit 200.

[0029] FIG. 4 shows an example of an image (dither matrix) after the dithering process is performed in the image signal generation unit 100 of this embodiment. In this example, images in the case where dithering processes with area ratios of 11%, 33%, 50%, and 66% are performed are shown. The CPU 102 forms a tone image by repeatedly arranging dither matrices having a size of 6 pixels in the vertical direction and 6 pixels in the horizontal direction as shown in FIG. 4.

[0030] As shown in FIG. 4, in the image after dithering processing, with respect to the change in the area ratio, the continuous count value of ON pixels changes complexly. Specifically, when the area ratio is 11%, only a continuous count of 2 ON pixels (an ON pixel group with a continuous count of 2) occurs, and when the area ratio is 33%, a continuous count of ON pixels from 1 to 3 pixels (an ON pixel group with a continuous count of 1 to 3) occurs. Also, when the area ratio is 50%, only a continuous count of 3 ON pixels (an ON pixel group with a continuous count of 3) occurs, and when the area ratio is 66%, a continuous count of ON pixels from 1 to 5 pixels (an ON pixel group with a continuous count of 1 to 5) occurs.

[0031] In this embodiment, the pixel sample timing period is set to be the same as the image clock period. Therefore, regarding the number of consecutive pixels (ON pixels), it is counted (acquired) as the ON consecutive count value.

[0032] <Predicted value of ON consecutive count value> In the image forming apparatus 9 of this embodiment, for the processing area (dithering processing unit) where dithering processing is performed, a predicted value of the ON consecutive count value is acquired (calculated) using the OFF consecutive count value and the size of the dither matrix. The size of the dither matrix refers to the size of the basic unit of dither that is repeatedly arranged in a pattern where pixel groups in the vertical and horizontal directions are determined by the execution of dithering processing. In this embodiment, as described above, in the pixel count unit 202, pixel count processing is performed based on the VDO signal 110. Therefore, the size of the dither matrix in the main scanning direction (horizontal direction) is used for calculating the predicted value of the ON consecutive count value.

[0033] The predicted value of the ON consecutive count value is, for example, (Size of dither matrix × Pixel sample timing period / Image clock period) - OFF consecutive count value is calculated by. Note that if a value similar to the ON consecutive count value can be obtained as a result by using the repeatability of the dither matrix used for dithering processing and the size of the dither matrix, a method other than this calculation method may be used.

[0034] In an image where dithering (halftone processing) is performed, generally, the majority of consecutive OFF pixels in the image have a consecutive count smaller than the size of the dither matrix used for dithering. This is because there are almost no images that intentionally create small blanks (blanks in pixel units), and the occurrence of repeated consecutive OFF pixels due to dithering becomes dominant. Therefore, the ON consecutive count value (predicted value) in the dithering unit also becomes smaller than the size of the dither matrix used for dithering.

[0035] In this embodiment, a method for correcting toner consumption using the ON consecutive count value in the dithering unit, which is smaller than the size of the dither matrix used for dithering, will be described.

[0036] <Method for Correcting Toner Consumption> In this embodiment, the pixel counting unit 202 (consecutive counter 226) sets a consecutive count (discrimination consecutive count) to be discriminated for obtaining the OFF consecutive count value, which is smaller than the size of the dither matrix. In this example, as shown in FIG. 4, a dither matrix with a size of 6 pixels in the horizontal direction and 6 pixels in the vertical direction is used for dithering. Therefore, five values of 1, 2, 3, 4, and 5, which are smaller than the size of the dither matrix, are set as the discrimination consecutive counts for the OFF consecutive count value. The pixel counting unit 202 (consecutive counter 226) is configured to obtain the OFF consecutive count value corresponding to each set discrimination consecutive count. Also, the discrimination consecutive count for the ON consecutive count value (predicted value) in the dithering unit is set to a value (5, 4, 3, 2, and 1) obtained by subtracting the discrimination consecutive count for the OFF consecutive count value from the size of the dither matrix. Hereinafter, the ON consecutive count values in the dithering unit corresponding to the discrimination consecutive counts 5, 4, 3, 2, and 1 are denoted as C5, C4, C3, C2, and C1 in order.

[0037] Here, using an image where only halftone processing is performed, the ON consecutive count value (predicted value) in the dithering unit is compared with the ON consecutive count value obtained by actually counting consecutive ON pixels. FIG. 5 shows an example of obtaining ON consecutive count values C1 to C5 in the dithering unit. In this example, the image after dithering for each area ratio shown in FIG. 4 is used as the image to be processed, and the counting process is performed on an image in which 100 images are repeatedly arranged in the vertical direction (direction orthogonal to the main scanning direction) and the horizontal direction (main scanning direction). For example, when the length of one side of a (square) 1 pixel is about 42.3 μm, an image of a square with a side length of 25.4 mm becomes the image to be processed.

[0038] As shown in FIG. 5, regardless of the area ratio, the error between the ON consecutive count values (predicted values) C1 to C5 in the dithering unit and the actual ON consecutive count values is small. Thus, even for an image after dithering with a size of about 25.4 mm, the ON consecutive count value (predicted value) obtained from the OFF consecutive count value and the size of the dither matrix can be used for correcting the toner consumption instead of the actual ON consecutive count value. The above-mentioned error may occur due to the start or end part of the dither repetition. Therefore, the larger the image area to be subjected to halftone processing (dithering), the smaller the error can be.

[0039] In the area such as the character part other than the dithering unit in the image corresponding to the VDO signal 110, the ON consecutive count value increases more than that in the dithering unit, but the OFF consecutive count value hardly increases. On the other hand, in the dithering unit, it can be said that it is more suitable for improving the prediction accuracy to use the ON consecutive count value (predicted value) obtained from the OFF consecutive count value and the size of the dither matrix for correcting (predicting) the toner consumption rather than the actual ON consecutive count value.

[0040] In this embodiment, for each ON pixel in the image corresponding to the VDO signal 110, correction (prediction) of the toner consumption amount is performed by applying a correction coefficient for the toner consumption amount. For this purpose, based on the ON continuous count value (predicted value) in the dithering processing unit, the total number of ON pixels in the dithering processing unit is obtained. Specifically, the total number of ON pixels in the dithering processing unit can be obtained by multiplying the ON continuous count values C1 to C5 in the dithering processing unit by the corresponding discrimination continuous numbers (that is, C5×5, C4×4, C3×3, C2×2, C1×1).

[0041] FIG. 6 shows an example of a correction coefficient used to obtain the toner consumption amount in the image formation of the target image in this embodiment and the comparative example. The correction coefficients in this embodiment and the comparative example are values normalized such that the consumption amount per pixel in a vertical line image in which 6 ON pixels and 144 OFF pixels are repeated in the vertical direction is 1. This image is used as a reference image for normalizing the toner consumption amount. The correction coefficient for the toner consumption amount per pixel of this reference image is defined as the normalized correction coefficient. By performing such normalization, the unit of the toner consumption amount becomes the number of pixels in the reference image.

[0042] In this embodiment, the prediction of the toner consumption amount is performed by multiplying the total number of ON pixels based on the predicted value of the ON continuous count value in the dithering processing unit by the normalized correction coefficient for each discrimination continuous number, and then obtaining the sum of the values obtained for each discrimination continuous number. The sum thus obtained is acquired as the predicted toner consumption amount (predicted value of the toner consumption amount) in the dithering processing unit.

[0043] For example, for the area ratio of 33% in FIGS. 4 and 5, the predicted toner consumption amount for the image after dithering processing is 0×1.3 + 0×1.5 + 59400×0.8 + 39600×0.3 + 19800×0.1 = 61380 It is calculated as follows. Here, since the pixel count value (i.e., the total number of ON pixels included in the target image) is 120,000 (obtained from the ON continuous count value shown in FIG. 5), the normalized consumption is obtained as 61,380 / 120,000 = 0.512. According to this normalized consumption, a prediction result is obtained that the toner consumption per pixel is about half that of the reference image.

[0044] Note that as the area ratio approaches 100%, the OFF continuous count value becomes extremely small, and the error in the prediction calculation of toner consumption may increase. Therefore, for example, when 90% or more of the OFF pixels in the dither processing unit are 1-pixel OFF pixels (not continuous), the correction of toner consumption using the correction coefficient may not be performed.

[0045] On the other hand, in the comparative example, the toner consumption is corrected using the OFF continuous count value for each discrimination continuous number. Thereby, regarding the point that toner is deposited on the OFF pixel portion (around the ON pixel) when the interval of ON pixels is narrow, the toner consumption is corrected. The correction coefficient (normalized correction coefficient) of the comparative example shown in FIG. 6 is obtained by examining the measurement of toner consumption while changing the interval (OFF pixel interval) between lines composed of 6 pixels in the vertical direction. Each correction coefficient in FIG. 6 is a correction coefficient applied to one OFF pixel. In the comparative example, the predicted toner consumption is obtained as (count value of ON pixels + predicted value of toner consumption for OFF pixels).

[0046] In the prediction of toner consumption based on OFF pixels, the total number of OFF pixels corresponding to each discrimination continuous number is obtained by OFF continuous count value × discrimination continuous number. Further, for each discrimination continuous number, the correction coefficient shown in FIG. 6 is multiplied by the total number of OFF pixels, and the sum of the obtained values is obtained to obtain the predicted value of toner consumption based on OFF pixels.

[0047] FIG. 7 shows examples of the pixel count value, the OFF continuous count value, and the total number of OFF pixels obtained using the dithered image with an area ratio of 66% in FIG. 4. The total number of OFF pixels is obtained by multiplying the discrimination continuous number by the OFF continuous count value. According to the example in FIG. 7, the predicted value of the toner consumption based on the OFF pixels is obtained as 20000×0.95 + 39600×0.5 + 59400×0 + 0×0 + 0×0 = 38800 using the correction coefficient shown in FIG. 6. Further, the predicted toner consumption is obtained as 240000 + 38800 = 278800. The normalized consumption is 278800 / 240000 = 1.162. Thus, when an image after dithering with an area ratio of 66% in FIG. 4 is formed, a prediction result is obtained that about 10% more toner is consumed compared to the reference image.

[0048] <Prediction accuracy> Next, the prediction accuracy of the toner consumption in the present embodiment and the comparative example will be described. FIG. 8 shows examples of the prediction results and the measured results of the toner consumption in the present embodiment and the comparative example. FIG. 8 shows the results obtained by the following experiment. Eighteen patterns of images (images with a width of 5100 pixels and a height of 6400 pixels) obtained by increasing the area ratio by 100 / 18 (≈5.55)% for each growth of a dither matrix with a size of 6 pixels in width and 6 pixels in height are prepared. Further, the images are output (printed) on 200 recording media of letter size each, and the measured value of the toner consumption is obtained by calculating the toner consumption per one ON pixel based on the decrease amount of toner from before output to after output. For the prediction of the toner consumption, the average value of the predicted values (predicted toner amounts) calculated by the above method is obtained.

[0049] In the graph of FIG. 8, the horizontal axis represents the area ratio of the input image, and the vertical axis represents the normalized consumption (per pixel). The plot of "□" represents the predicted value of the present embodiment, and the plot of "△" represents the predicted value of the comparative example. Also, the plot of "×" represents the value obtained by normalizing the toner consumption actually measured in the image forming apparatus 9. As described above, 18 patterns of images with different area ratios are used as the input images. When the normalized consumption is 1, it indicates that it corresponds to the toner consumption (per pixel) in the reference image. When the normalized consumption is less than 1, it indicates that it is less than the toner consumption (per pixel) in the reference image. Also, when the normalized consumption is greater than 1, it indicates that it is more than the toner consumption (per pixel) in the reference image.

[0050] The predicted value (normalized consumption) of the toner consumption in this comparative example is 1 due to the sufficient existence of the pixel interval up to about 50% of the area ratio of the input image. As the area ratio of the input image further increases from around 60%, a predicted value close to the measured value of the actual toner consumption is obtained based on the tendency of toner to adhere to the OFF pixels. In this comparative example, overall, the mean absolute error (MAE: Mean Absolute Error) between the predicted value and the measured value of the toner consumption is 0.313.

[0051] The predicted value of the toner consumption in the present embodiment increases up to about 70% of the area ratio as the area ratio of the input image increases. This is the same as the measured value of the actual toner consumption, indicating that high prediction accuracy is achieved. On the other hand, when the area ratio of the input image increases up to around 80%, the error between the predicted value and the measured value becomes large. This is because the prediction accuracy decreases due to the decrease in the number of OFF pixels included in the input image. Further, in the range from around 90% to 100% of the area ratio of the input image, the predicted value is 1 and almost coincides with the measured value. This is because when the area ratio is 90% or more, the condition for not performing the correction of the toner consumption using the correction coefficient is satisfied, so the correction of the toner consumption using the above correction coefficient is not performed.

[0052] In this embodiment, overall, the MAE between the predicted value and the measured value of the toner consumption is 0.101. Thus, according to the prediction of the toner consumption in this embodiment, it is possible to make the MAE between the predicted value and the measured value of the toner consumption smaller than that in the comparative example, and it is possible to improve the prediction accuracy.

[0053] Regarding the decrease in the prediction accuracy of the toner consumption in the comparative example, it is due to the fact that by correcting the toner consumption based on the OFF pixels, it is impossible to correct the point that the toner consumption for the ON pixels in the dithering processing unit becomes small. When the blank portion where no pixel is formed (no toner adheres) is large, although it is possible to set the correction coefficient to a negative value, using a correction coefficient that does not match the physical phenomenon to be predicted may cause a further decrease in the prediction accuracy. Also, by configuring the circuit to obtain the ON continuous count value as well, at the cost of an increase in the circuit cost within the apparatus, it is possible to improve the prediction accuracy of the toner consumption for the ON pixels. In that case, as in this embodiment, by also using the ON continuous count value (predicted value) in the dithering processing unit, it is possible to improve the prediction accuracy. This is because it is possible to set appropriate correction coefficients for the regions of the input image, such as the dithering processing unit and other character portions, using the ON continuous count value (predicted value) and the actual ON continuous count value in the dithering processing unit. (Refer to the second embodiment for this point.)

[0054] As described above, in the image forming apparatus 9 of this embodiment, the image signal generation unit 100 generates an image signal (VDO signal 110) by performing dithering processing as halftone processing on the input image. The control unit 200 acquires (predicts) the consumption amount of the developer for forming the developer image based on the image signal. The control unit 200 uses a count value (OFF continuous count value) obtained by individually counting OFF pixel groups composed of consecutive OFF pixels included in the image corresponding to the image signal, where the OFF pixel groups have different consecutive numbers, and the size of the dither matrix used for the dithering processing to acquire the consumption amount of the developer.

[0055] More specifically, the control unit 200 obtains, as a count value (ON consecutive count value) for an ON pixel group corresponding to a corresponding consecutive number in a processing area where dithering processing of an image is performed, a difference between the size of the dither matrix and a count value (OFF consecutive count value) for an OFF pixel group corresponding to each consecutive number. The control unit 200 further obtains the consumption amount of the developer based on the count value for the ON pixel group corresponding to each consecutive number.

[0056] In this way, using the size of the dither matrix used for dithering processing and the OFF consecutive count value, the ON consecutive count value corresponding to each consecutive number in the dithering processing unit is obtained, and based on the ON consecutive count value, the consumption amount of the developer is obtained (predicted). As a result, it becomes possible to more appropriately correct the consumption amount of the developer using the correction coefficient according to the consecutive number (size) of the ON pixel group, and it becomes possible to obtain (predict) the consumption amount with higher accuracy. Therefore, according to the present embodiment, when performing dithering processing on an input image, it is possible to prevent a decrease in the prediction accuracy of the consumption amount of the developer (toner).

[0057] For example, as the correction coefficient, a small correction coefficient is set for an ON pixel group with a small consecutive number, and a large correction coefficient is set for an ON pixel group with a large consecutive number. The control unit 200 applies such a correction coefficient corresponding to an individual consecutive number to the total number of ON pixels obtained based on the count value corresponding to the individual consecutive number for the ON pixel group. Further, the control unit 200 obtains the total sum of the consumption amounts corresponding to the individual consecutive numbers for the ON pixel group as the consumption amount of the developer for forming the developer image. By performing correction using such a correction coefficient, it becomes possible to improve the prediction accuracy of the consumption amount of the developer.

[0058] In addition, in this embodiment, the consumption amount of the developer can be obtained by using only the count value for the OFF pixel group corresponding to a continuous number smaller than the size of the dither matrix. Therefore, this embodiment also has the advantage that it does not require obtaining an OFF continuous count value corresponding to a larger continuous number in order to capture the characteristics of the image. Note that, in order to correct the consumption amount of the developer for regions other than the dither processing unit in the image corresponding to the image signal, other OFF continuous count values may be additionally used. In that case, correction is performed on the pixels having a count number obtained by subtracting the number of pixels in the dither processing unit from the total number of pixels in the entire image.

[0059] In this embodiment, for correcting the consumption amount of the developer, the ON continuous count values (predicted values) corresponding to each continuous number in the dither processing unit are weighted by a correction coefficient, but another algorithm may be used.

[0060] [Second Embodiment] In the second embodiment, an example of accurately obtaining the consumption amount of the developer (toner) for forming a developer image (toner image) by further using the ON continuous count value in addition to the configuration of the first embodiment will be described. Hereinafter, the description of the same parts as those in the first embodiment will be omitted, and the parts different from the first embodiment will be described.

[0061] In the pixel count unit 202 of this embodiment, as the discrimination continuous number N for the ON continuous count, a value smaller than the size of the dither matrix and a value larger than the size of the dither matrix are set. As an example, when the size of the dither matrix is 6, five values of N = 1, 2, 3, 4, 5 are set as the discrimination continuous number N smaller than the size of the dither matrix. Also, as the discrimination continuous number N larger than the size of the dither matrix, five values of N = 6, 7, 8, 9, 10 (a total of 10 values) are set. The ON continuous count values corresponding to these 10 discrimination continuous numbers N are sequentially designated as D1 to D10.

[0062] For the continuous count discriminant numbers N = 1 to 5, by obtaining the differences between the ON continuous count values D1 to D5 and the predicted values of the ON continuous count values in the dither processing unit, the ON continuous count values in the regions other than the dither processing unit can be obtained. In this case, it becomes possible to individually apply correction coefficients to the toner consumption amount obtained based on the ON continuous count value for the dither processing unit and the toner consumption amount obtained based on the ON continuous count value for the regions other than the dither processing unit (for example, the regions of small dots or thin lines can be separated and the correction coefficient can be applied to the regions). As a result, the prediction accuracy of the toner consumption amount can be improved.

[0063] FIG. 9 shows an example of the flow of predicting the toner consumption amount in the present embodiment. The prediction of the toner consumption amount is performed by the CPU 201 in the control unit 200. As shown in FIG. 9, based on the OFF continuous count values C1 to C5, in the same procedure as in the first embodiment, the predicted value of the ON continuous count value in the dither processing unit is obtained, and the toner consumption amount corrected using the first correction coefficient table is obtained.

[0064] Also, based on the ON continuous count values D1 to D5, as described above, the ON continuous count values corresponding to the ON pixel groups with a continuous number smaller than the size of the dither matrix in the regions other than the dither processing unit in the input image are obtained. Further, by multiplying each of the obtained ON continuous count values by the corresponding discriminant continuous number, the total number of corresponding ON pixels is obtained. Then, the correction coefficients included in the second correction coefficient table are multiplied by the total numbers of ON pixels (corresponding to the toner consumption amount) corresponding to different discriminant continuous numbers respectively. By obtaining the sum of the obtained values, the corrected toner consumption amount corresponding to the ON pixel group with a continuous number smaller than the size of the dither matrix is obtained.

[0065] Furthermore, the ON consecutive count values D6 to D10 correspond to ON consecutive count values corresponding to groups of ON pixels with a consecutive number larger than the size of the dither matrix in areas other than the dither processing section in the input image. By multiplying each of the ON consecutive count values D6 to D10 by the corresponding discrimination consecutive number, the total number of corresponding ON pixels is obtained. Thereafter, the correction coefficients included in the third correction coefficient table are multiplied by the total numbers of ON pixels (corresponding to toner consumption amounts) corresponding to different discrimination consecutive numbers, respectively. By obtaining the sum of the obtained values, the corrected toner consumption amount corresponding to a group of ON pixels with a consecutive number larger than the size of the dither matrix is obtained.

[0066] In the present embodiment, correction coefficients suitable for the dither processing section, groups of ON pixels with a small consecutive number in areas other than the dither processing section, and groups of ON pixels with a large consecutive number in areas other than the dither processing section are preset in the above-described first to third correction coefficient tables. Finally, the normalized consumption amount is obtained by dividing the sum of the obtained three toner consumption amounts by the pixel count value.

[0067] FIG. 10 shows an example of a correction coefficient for toner consumption amount obtained by an experiment on a dither processing section (image after dither processing) and a vertical line image. In this experiment, for the dither processing section, the same experiment as in the first embodiment is performed. On the other hand, for the vertical line image, ten vertical line images are prepared in which one to ten consecutive ON pixels and 144 consecutive OFF pixels are repeated. The image to be processed is an image with a horizontal pixel width of 5100 and a vertical pixel width of 6400.

[0068] In the graph of FIG. 10, the horizontal axis represents the number of consecutive pixels (the number of consecutive pixels), and the vertical axis represents the correction coefficient for toner consumption. The plot of "□" indicates the correction coefficient for the dither processing unit, and the plot of "△" indicates the correction coefficient for the line image. As shown in FIG. 10, for each number of consecutive pixels, the correction coefficient for the dither processing unit and the correction coefficient for the line image have different values. This indicates that even if the number of consecutive ON pixels is the same between the image after dither processing and the line image, the correction coefficients suitable for correcting toner consumption are different. Note that when the (predicted value) of the ON consecutive count value obtained from the OFF consecutive count value in the dither processing unit is not used, in the correction of toner consumption based on the ON consecutive count value, it is necessary to select one of the correction coefficients or use an intermediate value between them. This may lead to a decrease in prediction accuracy.

[0069] In the experiment of this embodiment, images are prepared so that the number of pixels is the same between the image after dither processing and the vertical line image. The image after dither processing is an image with an area ratio of 11%, and the vertical line image is a repetition of 2 ON pixels and 144 OFF pixels. The normalized consumption of toner consumption for these images was 0.6. Also, the normalized consumption (predicted value) obtained by predicting the toner consumption in this embodiment was 0.55. On the other hand, when the correction coefficient was applied only to the toner consumption based on the ON consecutive count value, the normalized consumption (predicted value) was 0.8. Thus, by appropriately applying the correction coefficient of toner consumption to both the image after dither processing and the line image, it is possible to improve the prediction accuracy of toner consumption.

[0070] As described above, in the image forming apparatus 9 of the present embodiment, the control unit 200 obtains the consumption amount of the developer (toner) using the count value (OFF continuous count value) obtained by individually counting different continuous numbers of OFF pixel groups included in the image corresponding to the image signal, the count value (ON continuous count value) obtained by individually counting different continuous numbers of ON pixel groups, and the size of the dither matrix used for dithering processing. In this way, by also using the ON continuous count value, it becomes possible to individually apply correction coefficients to the dithering processing unit and other regions in the image corresponding to the image signal to correct the consumption amount of the developer. As a result, it becomes possible to obtain (predict) the consumption amount with higher accuracy. Therefore, according to the present embodiment, when performing dithering processing on the input image, it is possible to prevent a decrease in the prediction accuracy of the consumption amount of the developer (toner).

[0071] [Third Embodiment] In the present embodiment, an example will be described in which the image signal generation unit 100 is configured to generate an image signal in which thinning of a part of each pixel developed by the developing device 3 is performed. Hereinafter, parts similar to those in the first embodiment will be omitted from the description, and parts different from the first embodiment will be described.

[0072] [Thinning Process of Part of Pixels] The image forming apparatus 9 of the present embodiment has a toner-saving mode for reducing the consumption amount of toner as an operation mode that can be set for image formation. In the present embodiment, the reduction of the toner consumption amount is performed by the image signal generation unit 100 generating the VDO signal 110 so as to thin out a part of each pixel (ON pixel). For example, thinning is performed on the regions at both ends of 10% in the main scanning direction of each pixel (so that the laser 302 is not emitted by the laser driving unit 300). As a result, the emission time of the laser 302 becomes 80% for each pixel in the input image, and the toner consumption amount per pixel is reduced.

[0073] FIG. 11 shows an example of an image corresponding to the VDO signal 110 generated by the image modulation unit 101 when the toner-saving mode is applied. In this example, thinning processing is performed on the image after dithering with an area ratio of 11% shown in FIG. 4, and it can be seen that thinning is performed at both ends in the main scanning direction of each ON pixel.

[0074] In this embodiment, as an example, for the setting of the image clock period of 50 MHz, the pixel sample timing period is set to 80 MHz. When the pixel sample timing period and the image clock period match, if the above-described thinning processing is performed, there may be pixels where counting is extremely not performed. For this reason, in this embodiment, the pixel sample period is made higher than the image clock period so that counting is performed one or more times for each pixel.

[0075] <Counting process when thinning process is applied> Next, examples of the ON continuous count value and the OFF continuous count value obtained by the counting process for the input image to which the above-described thinning process is applied will be described. FIG. 12 shows examples of the ON continuous count value and the OFF continuous count value obtained by experiments for each discrimination continuous number. In this experiment, an image in which 100 pixel groups each consisting of 4 consecutive pixels are arranged is used.

[0076] When no thinning process is performed on the input image, under the conditions of an image clock period of 50 MHz and a pixel sample timing period of 80 MHz, the ON pixel group corresponding to the discrimination continuous number 6 or 7 is counted, and the average ON continuous count value is 6.4. On the other hand, even when the thinning process is performed on the input image, it is desirable that a similar value be obtained as the average ON continuous count value.

[0077] As shown in FIG. 12, the continuous ON pixel groups that are counted become pixel groups with discrimination consecutive numbers of 1 to 4. This is because the pixel sampling timing overlaps with the positions where thinning is performed, causing the continuous counting of ON pixels to end. In this case, it is not possible to correct the toner consumption based on the desired ON continuous count value, nor can an appropriate correction coefficient be set.

[0078] On the other hand, when obtaining the OFF continuous count value, since the counting of OFF pixels is performed in the first place, it is less affected by performing thinning on a part of the pixels. Therefore, in this embodiment, even if the image forming apparatus 9 is configured to perform the thinning process as described above, by obtaining the ON continuous count value from the OFF continuous count value and predicting the toner consumption, a decrease in prediction accuracy can be prevented.

[0079] In this embodiment, as an example of performing the thinning process as described above, the toner-saving mode has been described. However, the thinning process may be performed by other processes. For example, in an image forming apparatus not equipped with an fΘ lens, there may be a process of making the density uniform by changing the thinning amount of pixels in the longitudinal direction by image processing. Even in such a case, this embodiment is applicable.

[0080] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiment to a system or apparatus via a network or a storage medium, and having one or more processors in the computer of the system or apparatus read and execute the program. It can also be realized by a circuit (for example, an ASIC) that realizes one or more functions.

[0081] The disclosure of this specification includes the following image forming apparatus, its control method, and program. (Item 1) An image forming apparatus, a photoreceptor, processing means for generating an image signal by performing dither processing as halftone processing on an input image, Exposure means for forming an electrostatic latent image on the photoreceptor by exposing the photoreceptor based on the image signal; Development means for forming a developer image on the photoreceptor by developing the electrostatic latent image using a developer; Acquisition means for acquiring the consumption amount of the developer for forming the developer image based on the image signal, comprising: The acquisition means uses a count value obtained by individually counting OFF pixel groups composed of consecutive OFF pixels included in the image corresponding to the image signal, and the size of the dither matrix used for the dithering process, to acquire the consumption amount. An image forming apparatus. (Item 2) The acquisition means: Obtains the difference between the size of the dither matrix and the count value for the OFF pixel group corresponding to each consecutive number as the count value for the ON pixel group corresponding to the corresponding consecutive number in the processing area where the dithering process of the image is performed, And acquires the consumption amount based on the count value for the ON pixel group corresponding to each consecutive number. The image forming apparatus according to Item 1. (Item 3) The acquisition means acquires a count value for an ON pixel group having a consecutive number smaller than the size of the dither matrix in the processing area where the dithering process is performed within the image. The image forming apparatus according to Item 2. (Item 4) The acquisition means acquires the consumption amount corresponding to each individual consecutive number by applying a correction coefficient corresponding to each individual consecutive number to the total number of ON pixels obtained based on the count value corresponding to each individual consecutive number for the ON pixel group. The image forming apparatus according to Item 3. (Item 5) The acquisition means acquires the sum of the consumption amounts corresponding to the individual consecutive numbers for the ON pixel group as the consumption amount of the developer for forming the developer image. The image forming apparatus according to Item 4. (Item 6) As the correction coefficient, a small correction coefficient is set for a group of ON pixels with a small consecutive number, and a large correction coefficient is set for a group of ON pixels with a large consecutive number. The image forming apparatus according to item 4 or 5. (Item 7) The acquisition means further acquires a pixel count value obtained by counting ON pixels included in the image corresponding to the image signal, and acquires a normalized consumption amount based on the consumption amount and the pixel count value. The image forming apparatus according to any one of items 1 to 6. (Item 8) The acquisition means acquires the consumption amount by using a count value obtained by separately counting OFF pixel groups with different consecutive numbers included in the image corresponding to the image signal, a count value obtained by separately counting ON pixel groups with different consecutive numbers, and the size of a dither matrix used for the dither process. The image forming apparatus according to any one of items 1 to 7. (Item 9) The processing means is configured to generate an image signal in which thinning is performed on a part of each pixel developed by the developing means. The image forming apparatus according to any one of items 1 to 8. (Item 10) A control method for an image forming apparatus, comprising: A processing step of generating an image signal by performing dither processing as halftone processing on an input image; An exposure step of forming an electrostatic latent image on the photoreceptor by exposing the photoreceptor based on the image signal; A developing step of forming a developer image on the photoreceptor by developing the electrostatic latent image using a developer; An acquisition step of acquiring a consumption amount of a developer for forming the developer image based on the image signal. In the acquisition step, the consumption amount is acquired by using a count value obtained by individually counting OFF pixel groups composed of consecutive OFF pixels included in the image corresponding to the image signal, and the size of the dither matrix used for the dither processing, in a control method of an image forming apparatus. (Item 11) A program for causing a computer to execute the control method of the image forming apparatus according to Item 10.

[0082] The invention is not limited to the above embodiments, and various changes and modifications are possible without departing from the spirit and scope of the invention. Therefore, the claims are attached to disclose the scope of the invention.

Description of Reference Numerals

[0083] 9: Image forming apparatus, 3: Developing device, 4: Photosensitive drum (photoconductor), 100: Image signal generation unit, 200: Control unit, 201: CPU, 202: Pixel count unit, 300: Laser drive unit, 400: Optical scanning unit

Claims

1. An image forming apparatus, comprising: a photoreceptor; processing means for generating an image signal by performing dither processing as halftone processing on an input image; exposure means for forming an electrostatic latent image on the photoreceptor by exposing the photoreceptor based on the image signal; development means for forming a developer image on the photoreceptor by developing the electrostatic latent image using a developer; acquisition means for acquiring a consumption amount of the developer for forming the developer image based on the image signal, wherein the acquisition means uses a count value obtained by individually counting OFF pixel groups composed of consecutive OFF pixels included in an image corresponding to the image signal, and the size of a dither matrix used for the dither processing, to acquire the consumption amount.

2. The acquisition means: acquires, as a count value for an ON pixel group corresponding to a corresponding consecutive number, a difference between the size of the dither matrix and the count value for the OFF pixel group corresponding to each consecutive number, in a processing area where the dither processing of the image is performed; acquires the consumption amount based on the count value for the ON pixel group corresponding to each consecutive number. The image forming apparatus according to claim 1.

3. The acquisition means acquires a count value for an ON pixel group having a consecutive number smaller than the size of the dither matrix in a processing area where the dither processing is performed within the image. The image forming apparatus according to claim 2.

4. The acquisition means acquires a consumption amount corresponding to an individual consecutive number by applying a correction coefficient corresponding to the individual consecutive number to the total number of ON pixels obtained based on the count value corresponding to the individual consecutive number for the ON pixel group. The image forming apparatus according to claim 3.

5. The acquisition means acquires, as the consumption amount of the developer for forming the developer image, the sum of the consumption amounts corresponding to the individual consecutive numbers for the ON pixel group. The image forming apparatus according to claim 4.

6. As the correction coefficient, a small correction coefficient is set for an ON pixel group having a small consecutive number, and a large correction coefficient is set for an ON pixel group having a large consecutive number. The image forming apparatus according to claim 4.

7. The acquisition means further acquires a pixel count value obtained by counting ON pixels included in the image corresponding to the image signal, and acquires a normalized consumption amount based on the consumption amount and the pixel count value. The image forming apparatus according to any one of claims 1 to 6.

8. The acquisition means acquires the consumption amount by using a count value obtained by separately counting OFF pixel groups having different consecutive numbers included in the image corresponding to the image signal, a count value obtained by separately counting ON pixel groups having different consecutive numbers, and the size of the dither matrix used for the dither process. The image forming apparatus according to any one of claims 1 to 6.

9. The processing means is configured to generate an image signal in which thinning is performed on a part of each pixel developed by the developing means. The image forming apparatus according to any one of claims 1 to 6.

10. A control method for an image forming apparatus, comprising: a processing step of generating an image signal by performing dither processing as halftone processing on an input image; an exposure step of forming an electrostatic latent image on the photoreceptor by exposing the photoreceptor based on the image signal; a developing step of forming a developer image on the photoreceptor by developing the electrostatic latent image using a developer; an acquisition step of acquiring a consumption amount of the developer for forming the developer image based on the image signal, wherein in the acquisition step, the consumption amount is acquired by using a count value obtained by separately counting OFF pixel groups composed of consecutive OFF pixels included in the image corresponding to the image signal, the OFF pixel groups having different consecutive numbers, and the size of the dither matrix used for the dither process. A control method for an image forming apparatus.

11. A program for causing a computer to execute the control method of the image forming apparatus according to claim 10.

Images