JP2012150275A - Image processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing device that suppresses an increase in a toner adhesion amount by combined use of dark and light toners.SOLUTION: In an image processing device, a Bk/Lk color separation unit 113 divides a K signal (black image signal) into an Lk signal (light toner image signal) and a Bk signal (dark toner image signal). An Lk use control unit 114 executes comparison determination by pixel with respect to a value of the Bk signal and a determination threshold value, and instructs a half tone processing unit 109 to suppress use of an Lk toner (light black toner) at a pixel whose Bk signal value is equal to or larger than the determination threshold value. In an output engine 110, regarding a dark black toner, a value of the Bk signal for stably obtaining a predetermined toner adhesion amount is set as the determination threshold value.

Description

  The present invention relates to an image processing apparatus including an image forming unit that uses light toner and dark toner for a specific color.

  In electrophotographic image formation, the density of a recorded image is expressed by an increase or decrease in the amount of toner adhered per unit area. In the highlight area (low density area) where the toner adhesion amount is small, the toner adhesion amount is unstable and the density is unstable. Therefore, dark and light toners of the same color (for example, black dark and light toner) can be used, and in the highlight area, the toner adhesion amount is increased by using the light toner to stabilize the density, which is higher than a certain density. In the density range, a technique for improving gradation by using both dark toner and light toner is known (see Patent Document 1).

  However, in such a system using dark and light toners, the usage ratio of dark and light toners is gradually switched in the density range where the light toner and dark toner are switched. There is a problem that the total toner adhesion amount) is increased as compared to the case of using only the dark toner.

  An object of the present invention is an image processing apparatus including an image forming unit that can use toners of a plurality of colors for image formation and that can use dark and light toners for a specific color among the plurality of colors. An object of the present invention is to improve the problem of increase in the amount of toner adhesion in the dark and light toner switching density region as described above.

  The image processing apparatus according to the present invention can use a plurality of colors of toner for image formation, and can use light toner and dark toner for a specific color among the plurality of colors. An image signal corresponding to the specific color (referred to as a pre-separation image signal) to an image signal corresponding to the light toner of the color (referred to as a light toner image signal) and a dark toner of the color. A means for decomposing into a corresponding image signal (referred to as a dark toner image signal), comparing the value of the dark toner image signal of the specific color or the pre-separation image signal with a determination threshold value for the color for each pixel, Means for suppressing use of light toner of the color, and a determination threshold value for setting the determination threshold value for a pixel for which the value of the color dark toner image signal or the pre-separation image signal is determined to be equal to or greater than the determination threshold value for the color Has setting means And wherein the Rukoto.

  In the image forming unit, the adhesion amount of the dark toner is stabilized when it exceeds a predetermined amount. In the image processing apparatus of the present invention, if the value of the dark toner image signal or the pre-decomposition image signal for obtaining such a predetermined toner adhesion amount is set as the determination threshold value, the dark toner adhesion amount is stabilized. Since the use of light toner in a certain density range is suppressed, the toner adhesion amount can be reduced compared to the conventional technology in which dark and light toner are used in combination, and the use of light toner is also possible. Is suppressed in a density range in which the amount of dark toner adhered is stable, so that density stability can be secured.

1 is a block diagram of an image processing apparatus according to an embodiment of the present invention. It is a mimetic diagram for explaining an example of an output engine. It is a graph which shows an example of a Bk * Lk separation table. It is a graph which shows another example of a Bk * Lk separation table. It is explanatory drawing of the light source and light receiving element for a toner adhesion amount monitor. FIG. 6 is a schematic diagram for explaining an example of a toner adhesion amount monitoring pattern. It is a flowchart which shows the processing flow relevant to a color conversion unit, a halftone process part, and a Lk use control part. FIG. 6 is a diagram schematically illustrating an adhesion state of Lk toner and Bk toner.

  FIG. 1 is a functional block diagram of an image processing apparatus according to an embodiment of the present invention. As shown in FIG. 1, the image processing apparatus includes a scanner 101, a scanner γ correction unit 102, an input masking unit 103, a filter processing unit 104, a storage unit 106, a color conversion unit 107, a halftone processing unit 109, and an output engine. (Image forming means) 110, Lk use control unit 114, control unit 120, operation unit 121, and toner adhesion amount determination unit 127.

  It should be noted that an interface with an external device such as a personal computer can be provided so that image data can be input from the external device and the image can be output. An image processing apparatus having such a configuration is also included in the present invention. .

  FIG. 2 is a schematic diagram showing an example of the output engine 110. The output engine 110 shown here is a well-known electrophotographic image forming means, which is a C plate imaging station 35 using C (cyan) toner, an M plate imaging station 36 using M (magenta) toner, Y Y plate image forming station 37 using (yellow) toner, Bk plate image forming station 38 using Bk (dark black) toner, Lk plate image forming station 39 using Lk (light black) toner, intermediate transfer belt 40, secondary A transfer charger 41, an intermediate transfer cleaner 42, a fixing device 43, and a paper feed roller 2, a transport roller pair 3, and a registration roller pair 4 related to paper feed transport of the recording paper 1 are provided.

  Each of the plate image forming stations 35, 36, 37, 38, 39 has the same configuration, and the chargers 6, 11, 17, 23, 29 and the chargers 6, 12 for uniformly charging the surfaces of the photosensitive members. 18, 24, 30, a writing unit (not shown) that irradiates exposure beams 7, 13, 19, 25, 31 for forming an electrostatic latent image of each plate on the surface of the charged photoreceptor, Developers 8, 14, 20, 26, 32 for developing the formed electrostatic latent image into a toner image, and primary transfer chargers 10, 16, 22 for transferring the toner image of each plate from the photoreceptor to the intermediate transfer belt 40. , 28, 34, and cleaning blades 9, 15, 21, 27, 33 for removing toner remaining on the photoreceptor without being transferred.

  Such an image forming operation of the electrophotographic output engine 110 is general and will be described briefly. The stacked recording sheets 1 are separated and fed one by one by a sheet feeding roller 2 and conveyed to a pair of conveying rollers 3, and the recording sheet is further conveyed to a pair of registration rollers 4 by the conveying roller pair 3. The registration roller pair 4 is configured so that the rotation and stop of the roller can be freely controlled by a registration clutch (not shown). In order to wait for the completion of a series of image forming processes to be described later, the registration roller pair 4 temporarily records. Stop the paper.

  In each image forming station 35, 36, 37, 38, 39, the exposure beam 7, 13, 19, 25, 31 modulated by the recording signal of each plate output from the halftone processing unit 109 (FIG. 1). Is irradiated from a writing unit (not shown), and an electrostatic latent image of each plate is formed on the photoreceptors 5, 11, 17, 23, and 29, and toner development is performed. The developed toner images of the respective plates are transferred onto the intermediate transfer belt 40 by the primary transfer chargers 10, 16, 22, 28, and 34. When all the toner images of the plates are transferred to the intermediate transfer belt 40, the recording paper once stopped by the registration roller pair 4 is transported again in time, and all the toner images are transferred onto the recording paper by the secondary transfer charger 41. A plate toner image is transferred. The recording paper to which the toner image has been transferred is conveyed to the fixing device 43, where the unfixed toner image is fixed on the recording paper by heat and pressure. The toner remaining on the intermediate transfer belt 40 is scraped off by the intermediate transfer cleaner 42.

  Returning to FIG. The digital color image signal input by the scanner 101 is converted from a linear reflectance signal into a linear density signal by the scanner γ correction unit 102, and further, the input masking unit 103 converts the signal dependent on the input device into a device-independent signal. It is converted into a standard image signal. The filter processing unit 104 corrects the spatial frequency characteristics for this image signal (here, RGB signals). Specifically, an edge enhancement filter is applied to an image that requires sharpness such as characters, and a smoothing filter is applied to an image that requires smoothness such as a photograph. The image signal corrected as described above is temporarily stored in the storage unit 106.

  The image signal stored in the storage unit 106 is read out and input to the color conversion unit 107. The color conversion unit 107 converts an image signal input as an RGB signal, which is a standard signal, into a device-dependent image signal corresponding to each color toner (color material) used in the output engine (image forming unit) 110. It is.

  In this embodiment, as described above, the output engine 110 is of an electrophotographic system, and includes three types of color toners of cyan (C), magenta (M), and yellow (Y), dark black (Bk), In this configuration, two types of black toner, light black (Lk), are used to form an image. Therefore, the input RGB signal is converted by the color conversion unit 107 into a C signal, an M signal, a Y signal, a Bk signal, and an Lk signal that are image signals corresponding to each toner used in the output engine 110. These toner-corresponding image signals are subjected to halftone processing (dither processing and error diffusion processing) by the halftone processing unit 109, and the processed signals are written to the writing units ( (Not shown) is supplied as a recording signal for each plate.

  In addition, although it is Lk toner, in order to ensure the density stability against fluctuations in the amount of adhesion, it is manufactured by mixing a white material (for example, titanium oxide) with a colorant (for example, black pigment such as carbon) of the Bk toner. As in the case of the Bk toner, the Lk toner having the characteristic that the density is saturated with a fixed amount or more is used. The Bk toner is assumed to be saturated with a density of 2.0 at an adhesion amount of 0.9 (mg / cm ^ 2) or more, for example, and the Lk toner is an adhesion amount of 1.0 (mg / cm ^ 2) or more, for example. And the concentration is saturated to 1.2. The density at the time of saturation can be adjusted by increasing or decreasing the amount of the colorant and white material in the toner.

The color conversion unit 107 according to this embodiment includes a color conversion unit 111, a black generation unit 112, and a Bk / Lk separation unit 113. The color conversion unit 111 is a unit that converts the device-independent RGB signal input to the color conversion unit 107 into a device-dependent CMY signal. Various methods can be used for this color conversion. Here, for example, a masking operation as shown in the following equation is performed.
C = α11 × R + α12 × G + α13 × B + β1
M = α21 × R + α22 × G + α23 × B + β2
Y = α31 × R + α32 × G + α33 × B + β3 Formula (1)
Here, α11 to α33 and β1 to β3 are predetermined color correction coefficients, and CMY is 8 bits each for RGB 8-bit signals (having values from 0 to 255).

The black generating unit 112 is a unit that generates a black (K) signal from the CMY signal. Here, the K signal (8 bits) is obtained by the following equation.
K = Min (C, M, Y) Equation (2)
That is, a common component of each of the C, M, and Y signals, that is, a gray (black) component is extracted, and all gray components are output as a K signal.

  The black generation unit 112 includes so-called background removal processing (UCR) means, and outputs C, M, and Y signals obtained by subtracting the K signal component (black component) from the C, M, and Y signals input from the color conversion unit 111. Output to the halftone processing unit 109. The background removal processing unit may be independent of the black generation unit 112 and provided between the black generation unit 112 and the halftone processing unit 109.

  The Bk / Lk separation unit 113 decomposes the K signal (black pre-decomposition image signal) into a Bk signal (black dark toner image signal) and an Lk signal (black light toner image signal) (the K plate is converted into the Bk plate). And Lk version).

  An example of a separation table used in the Bk / Lk separation unit 113 is shown in FIG. FIG. 3 assumes a case in which the characteristics regarding the Lk and Bk toner adhesion amounts in the output engine 110 are standard, with the K signal value (0 to 255) as the horizontal axis, the Lk toner adhesion amount corresponding to the Lk signal value. A thin broken line 131 is a graph in which the Bk toner adhesion amount corresponding to the Bk signal value is plotted as a thick broken line 132. A solid line 133 plots the toner adhesion amount when only Bk toner is used in the entire density range. In addition, the part which overlaps with the solid line 133 of the thick broken line 132 is represented as a solid line.

  In this separation table, for example, the Lk signal value gradually increases as the K signal value increases in the range of 0 ≧ K signal value <128, and when the K signal value = 128, the Lk signal value is saturated to the maximum value. The Lk signal value maintains the maximum value in the range of 128 <K signal value ≦ Kb (for example, Kb = 140), and the Lk signal becomes 0 in the range of Kb <K signal value ≦ 255. When the K signal value is less than Ka (for example, Ka = 110), the Bk signal value is 0. When the K signal value is in the range of Ka or more, the Bk signal value increases as the K signal value increases, and the K signal value = 255. Bk signal value = 255. However, the Lk signal value may be maintained at a saturated value in a region where the K signal value exceeds Kb, for example, in a region where Kb <K signal value ≦ 255.

  FIG. 4 is a graph similar to FIG. 3 showing another example of the separation table. In this separation table, the Bk signal value is raised from Ka ′ smaller than Ka in FIG. 3, and the K signal value range in which Lk toner and Bk toner are used together is expanded. Along with this, the Lk signal value changes gently as shown by a thin broken line 131 ′, and the Bk signal value changes gradually as compared with the example of FIG. 3, as shown by a thick broken line 132 ′. The rest is the same as the example of FIG.

  In general, a color separation table that uses a large amount of Lk toner as shown in FIG. 3 is suitable for a halftone image such as a photograph, and a color separation table such as that shown in FIG. 4 that uses a large amount of Bk toner is a character image. Suitable for.

  In the present embodiment, the control unit 120 includes a color separation table selection signal generation unit 122 that generates a selection signal for selecting one of the two color separation tables to be used by the Bk / Lk color separation unit 113. When the photographic mode suitable for a halftone image such as a photographic image is designated by the operation unit 121, control is performed to select the separation table of FIG. 3, and the character mode suitable for the character image is designated. In this case, control is performed so as to select the sorting table of FIG. Three or more types of separation tables corresponding to three or more modes are provided in the Bk / Lk separation unit 113, and the corresponding one of the three or more types of separation tables is selected according to the mode specified by the operation unit 121. The plate table can be selectively used, and such an aspect is also included in the present invention.

  A major feature of the image processing apparatus according to the present embodiment is that it is possible to control the use of Lk toner in a density range where the adhesion amount of Bk toner is stable. Prepare. The Lk use control unit 114 sets the value of the Bk signal output from the Bk / Lk separation unit 113 and the determination threshold Th (related to black) set by the determination threshold setting unit 123 in the control unit 120 for each pixel. If the Bk signal value is determined to be greater than or equal to the determination threshold Th, the halftone processing unit 109 is instructed to inhibit the use of Lk toner for the pixel.

  In the output engine 110, the Bk toner adhesion amount is stabilized when it exceeds a certain amount, but a Bk signal for obtaining such a stable predetermined Bk toner adhesion amount (corresponding to Q in FIGS. 3 and 4). Is set as the determination threshold Th. That is, the use of Lk toner is intermediately inhibited for pixels for which it is determined that the Bk toner adhesion amount corresponding to the value of the Bk signal is equal to or greater than the stable predetermined Bk toner adhesion amount (Q in FIGS. 3 and 4). The tone processing unit 109 is instructed.

  The determination threshold value setting unit 123 has two modes related to adjustment of the determination threshold value Th. The first mode is a manual adjustment mode in which the determination threshold Th is adjusted according to an instruction from the operation unit 121. The second mode is an automatic adjustment mode in which the determination threshold Th is automatically adjusted based on the result of toner adhesion amount determination for the Bk toner adhesion amount monitoring pattern recorded in the output engine 110.

  In connection with the automatic adjustment mode of the determination threshold, the output engine 110 records a pattern signal (Bk) for recording a Bk toner adhesion amount monitoring pattern (a pattern for confirming the correspondence between the Bk signal value and the Bk toner adhesion amount). Signal) to the halftone processing unit 109 is provided in the control unit 120. Further, as shown in FIG. 2, the output engine 110 includes a light receiving element 125 and a light source 126 for detecting the Bk toner adhesion amount of the Bk toner adhesion amount monitoring pattern recorded with Bk toner. In addition, a toner adhesion amount determination unit 127 that determines whether the Bk toner adhesion amount of the Bk toner adhesion amount monitoring pattern matches a predetermined Bk toner adhesion amount from the detection output signal of the light receiving element 125 is provided. The provision of means related to such an automatic adjustment mode of the determination threshold is also a major feature of the image processing apparatus according to the present embodiment.

  When recording a Bk toner adhesion amount monitoring pattern, a pattern signal (Bk signal) is input to the halftone processing unit 109 from the pattern signal generating means 124 (FIG. 1), and the recording signal subjected to the halftone processing is printed on the Bk plate. An electrostatic latent image of a Bk toner adhesion amount monitor pattern is formed on the photosensitive member 23 by an exposure beam that is input to the writing unit of the image station 38 and modulated according to the recording signal, and the Bk toner image is intermediately transferred. Transferred to the belt 40. Such a pattern is preferably recorded on the side end portion of the intermediate transfer belt 40 (a portion outside a region where a toner image of a normal image is transferred). The light receiving element 125 is provided at a position facing a region where the toner image of the pattern of the intermediate transfer belt 40 is transferred.

  FIG. 5 is a schematic diagram showing the relationship between the light source 126, the light receiving element 125, and the Bk toner adhesion amount monitoring pattern image (Bk toner image) 45 on the intermediate transfer belt 40. As shown in the drawing, illumination light is irradiated in the vertical direction from the light source 126 toward the pattern image 45, and reflected light in the oblique direction is received by the light receiving element 125.

  When the Bk signal value input to the halftone processing unit 109 is gradually increased from 0, the output engine 110 obtains a stable predetermined Bk toner adhesion amount (Bk toner adhesion amount Q in FIGS. 3 and 4). A plurality of patches corresponding to the Bk signal value expected to be obtained and several Bk signal values before and after that can be used as the Bk toner adhesion amount monitoring pattern. FIG. 6 shows an example of such a plurality of patches 45_1 to 45_4. Bk (i) written in each patch is a Bk signal value (used for recording) corresponding to the patch. The pattern signal is a Bk signal corresponding to the patch as described above. As the intermediate transfer belt 40 moves, the reflected light from each patch and the reflected light from the surface of the intermediate transfer belt 40 enter the light receiving element 125 in order.

  The toner adhesion amount determination unit 127 determines whether the Bk toner adhesion amount of each patch matches the predetermined Bk toner adhesion amount Q from the detection output signal of the light receiving element 125. Specifically, for example, the detection output signal value of the light receiving element 125 when the reflected light from the surface of the intermediate transfer belt 40 enters the light receiving element 125, and the reflected light from each patch enters the light receiving element 125. If the difference between this ratio and a predetermined value is less than a predetermined value, it is determined that the Bk toner adhesion amount of the patch matches the predetermined Bk toner adhesion amount Q. If the difference is equal to or greater than the predetermined value, it is determined that the Bk toner adhesion amount of the patch does not match the predetermined Bk toner adhesion amount Q. However, it is not necessarily limited to this method.

  In the automatic adjustment mode, the determination threshold setting unit 123 of the control unit 120 automatically adjusts the determination threshold based on the determination result of the toner adhesion amount determination unit 127. For example, in the test pattern shown in FIG. 6, when the toner adhesion amount determination unit 127 determines that the Bk toner adhesion amount of the patch 45_2 matches the predetermined Bk toner adhesion amount Q, the determination threshold setting unit 123 sets the patch 45_3. The Bk signal value Bk (2) corresponding to is set as the determination threshold Th.

  Now, the adhesion amount characteristic of each toner including Bk toner in the output engine 110 fluctuates due to changes in the environmental temperature, changes in the remaining amount of toner in the developing device, changes in the characteristics of the photoconductor and chargers, and various other factors. Therefore, the Bk signal value corresponding to a predetermined Bk toner adhesion amount (for obtaining it) varies. According to the above-described determination threshold automatic adjustment mode, the determination threshold Th can be appropriately automatically adjusted according to such fluctuations.

  The above-described automatic adjustment of the determination threshold is executed whenever necessary by the user instructing from the operation unit 121, or automatically executed when the apparatus is turned on, or whenever a set number of document images are output. It can be executed automatically. By changing the set number of sheets according to the density stability of the apparatus, the density stability of the apparatus may be reflected in the execution frequency of the automatic determination threshold adjustment. Further, the execution frequency can be changed according to the image quality mode. In a mode that emphasizes density stability, for example, a photo mode that emphasizes gradation, the execution frequency of the determination threshold automatic adjustment is increased (the number of the set number is reduced) to increase the determination threshold setting accuracy, and the density stability is increased. In a mode that does not place emphasis on, for example, a character mode that emphasizes character reproducibility, the execution frequency is reduced (the number of set images is increased).

  FIG. 7 shows a processing flow in units of pixels related to the color conversion unit 107, the halftone processing unit 109, and the Lk use control unit 114.

  RGB signals are read out from the storage unit 106 pixel by pixel and input to the color conversion unit 107 (step S1). The RGB signals are converted into CMY signals by the color conversion unit 111 (step S2). The black generation unit 112 generates a K signal from the CMY signal (step S3). In this step, the black generation unit 112 also executes a background removal process for subtracting the black component from the CMY signal. In the Bk / Lk separation unit 113, the K signal is decomposed (separated) into a Bk signal corresponding to dark black toner and an Lk signal corresponding to light black toner (step S4). The Lk usage control unit 114 determines whether the value of the Bk signal output from the Bk / Lk separation unit 113 is greater than or equal to the determination threshold Th set by the determination threshold setting unit 123 (step S5).

  When the determination result is Yes (when Bk signal value ≧ determination threshold Th, that is, when the Bk toner adhesion amount corresponding to the Bk signal value is equal to or larger than the stable predetermined Bk toner adhesion amount Q), the pixel concerned Since the Lk use control unit 114 instructs the halftone processing unit 109 to inhibit the use of the Lk toner, the halftone processing unit 109 outputs the image signal excluding the Lk signal, that is, the C, M, and Y signals after the background removal processing, Halftone processing is performed on the Bk signal (step S7). When the determination result is No (when Bk signal value <determination threshold Th, that is, when the Bk toner adhesion amount corresponding to the Bk signal value is smaller than the stable predetermined Bk toner adhesion amount Q), for the pixel concerned, Since the Lk use control unit 114 does not instruct the halftone processing unit 109 to inhibit the Lk toner use, the halftone processing unit 109 includes all image signals including the Lk signal, that is, the C, M, and Y signals after the background removal processing. , Bk signal and Lk signal are subjected to halftone processing (step S6).

  Reference is now made to FIGS. 3 and 4 again. When only Bk toner is used, the toner adhesion amount characteristic as shown by the solid line 133 is obtained. The toner adhesion amount is smaller than the predetermined toner adhesion amount Q, and the density stability is good in the low density region where the toner adhesion amount is unstable. Absent. In the present embodiment, the Lk toner (black light toner) is used in the low density region, thereby increasing the toner adhesion amount and improving the density stability. However, since the density of the Lk toner is lower than that of the Bk toner (black dark toner), only the Bk toner is used, as can be seen by comparing the thin broken lines 131 and 131 ′ and the solid line 133 in FIGS. Compared to the case, the toner adhesion amount in the low density region increases.

  In the density range where the K signal value exceeds Ka or Ka ′, the Bk toner adhesion amount is small and unstable, and in the area where the density stability is poor only with the Bk toner, the density is stabilized by using the Lk toner together. In the region where the adhesion amount of the Bk toner is equal to or more than the predetermined adhesion amount Q of the Bk toner, the use of the Lk toner is suppressed by the above-described control, thereby maintaining the density stability and suppressing the influence on the image quality. In addition, the toner adhesion amount can be reduced. In this embodiment, as can be seen from FIGS. 3 and 4, the predetermined Bk toner adhesion amount Q is equal to the Bk toner adhesion amount corresponding to the intersection of the thick broken lines 132, 132 ′ and the solid line 133.

  In the classification table of FIG. 4, compared to the classification table of FIG. 3, the Lk and Bk mixed color areas are widened and the gradation is stabilized in the rising area of the Bk toner, but the increase in the Lk signal value is moderate. As a result, the amount of Lk toner attached decreases, and the toner embedding on the paper tends to deteriorate. Therefore, in order to improve the toner filling on the paper in the Lk and Bk mixed color region, it is also effective to change the gradation processing pattern in the halftone processing unit 109 between the Lk signal and the Bk signal. For example, error diffusion can be used for the Lk signal, and halftone dots or line dither patterns can be used for the Bk signal. Since the Lk toner is intended to be used on the low density side, it is preferable to use error diffusion which does not cause a problem that the rising pattern formation becomes unstable, such as halftone dots and line dither. On the other hand, since Bk toner is used at a medium density or higher, it is preferable to use a dither pattern in which the patterns are aggregated. However, this is not the case in the image quality mode in which resolution is more important than gradation. It is also possible to use error diffusion for both Lk and Bk toners.

  FIG. 8 is a diagram schematically showing the adhesion state of the Lk and Bk toners.

  FIG. 8A shows a state in which only the Lk toner is attached on the paper. Here, the adhesion amount of the Lk toner is saturated, and the paper is entirely covered with the Lk toner. In this state, the density stability is good.

  FIG. 8B shows a mixed color state of the Lk and Bk toners, and the Bk toner adheres on the Lk toner that covers the entire surface of the paper. Even if the adhesion amount of the Bk toner is not stable, since the paper is entirely covered with the Lk toner, the toner amount including the Lk toner is stable and the density stability is good. Even if the paper is not entirely covered with Lk toner, the stability of density can be ensured by using a halftone processing pattern with good toner filling for Lk toner as described above.

  FIG. 8C shows a situation where only Bk toner is placed on the paper. Here, the adhesion amount of the Bk toner is in a saturated state, and the density is stable because the dark toner covers the paper. In the middle density area, the paper is not completely covered, but the gradation processing patterns are gathered to some extent and the number of isolated dots is small, so that density stability is ensured.

  Now, the Lk usage control unit 114 compares and determines the Bk signal value and the determination threshold for each pixel. However, since there is a certain correspondence between the value of the K signal before separation (image signal before black separation) and the value of the Bk signal after separation (black dark toner image signal), Lk is used. It is also possible to perform similar Lk toner usage control by changing the control unit 114 to compare the K signal value with the determination threshold value. In this case, a K signal value corresponding to the predetermined Bk toner adhesion amount Q in FIGS. 3 and 4 is set as the determination threshold. In the determination threshold automatic adjustment mode, for example, when the toner adhesion amount determination unit 127 determines that the Bk toner adhesion amount of the patch 45_2 shown in FIG. 6 is a predetermined Bk toner adhesion amount Q, the Bk corresponding to the patch is determined. The K signal value K (2) corresponding to the signal value Bk (2) is set as the determination threshold Th for black by the determination threshold setting means 123.

  In the embodiment described above, the K plate is divided into the Lk plate and the Bk plate, and the use of the Lk toner is restricted, but the present invention is not limited to this. For one or more color plates of C, M, and Y, the image signal after the background removal processing is separated into a dark toner signal and a light toner signal, and the dark toner signal has a determination threshold similar to that of the Bk signal. A comparison determination may be performed, and the use control of the light toner may be performed according to the result. The same light toner usage control may be performed for the K plate and one or more color plates of C, M, and Y. When the color plate of any one of C, M, and Y is divided into a dark and light plate and the determination threshold for performing use control for the light toner is automatically adjusted, the toner adhesion amount using the dark toner of that color A monitor pattern is recorded, and based on the determination result of the toner adhesion amount, a dark toner signal value corresponding to a predetermined toner adhesion amount (or a signal value before color separation corresponding to the dark toner signal value) is determined. What is necessary is just to set as a threshold value. In the case where dark and light toners are used for two or more colors and the same use suppression control is performed for the light toners, it is naturally necessary to set a determination threshold value for each color. That is, a comparison determination is performed between the value of the dark toner signal of each color (or the value of the signal before the color separation) and the determination threshold set for the color.

101 Scanner 102 Scanner γ Correction Unit 103 Input Masking Unit 104 Filter Processing Unit 106 Storage Unit 107 Color Conversion Unit 109 Halftone Processing Unit 110 Output Engine 111 Color Conversion Unit 112 Black Generation Unit 113 Bk / Lk Separation Unit 114 Lk Use Control Unit 120 Control Unit 121 Operation Unit 122 Separation Table Switching Unit 123 Determination Threshold Setting Unit 124 Pattern Signal Generation Unit 125 Light Receiving Element 126 Light Source 127 Toner Adhesion Amount Determination Unit

JP 2001-290319 A

Claims (2)

An image processing apparatus comprising an image forming unit capable of using a plurality of colors of toner for image formation and using a light toner and a dark toner for a specific color of the plurality of colors,
An image signal corresponding to the specific color (referred to as pre-separation image signal) is an image signal corresponding to the light toner of the color (referred to as a light toner image signal) and an image signal corresponding to the dark toner of the color (dark toner). Means called image signal),
The value of the dark toner image signal or the pre-separation image signal of the specific color is compared with the determination threshold value for the color for each pixel, and the value of the dark toner image signal or the pre-separation image signal of the color is determined for the color Means for suppressing the use of light toner of the color for pixels determined to be equal to or greater than a threshold;
And an image processing apparatus comprising determination threshold setting means for setting the determination threshold.   Means for determining whether or not the toner adhesion amount of the toner adhesion amount monitor pattern recorded by using the specific color dark toner in the image forming means matches a predetermined toner adhesion amount; Based on the result of the determination of the adhesion amount, the determination threshold setting unit determines the value of the dark toner image signal of the color for obtaining the predetermined toner adhesion amount for the dark toner of the specific color by the image forming unit or The image processing apparatus according to claim 1, wherein a value of an image signal before separation of the color with respect to the value is set as the determination threshold value for the color.

Images