JP2004289873A - Image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a tracking pattern from loosing the identifiability and latency even when the density of the recorded image to be formed changes. <P>SOLUTION: According to a deviation between the density resulting from measuring a toner patch and a target value, a look-up table to be used for gamma correction using a gamma correction circuit 204 is selected and separately therefrom, on the other hand, the tracking pattern to be added to inputted image data is selected. In such a case, the tracking pattern is selected to correct the form of the tracking pattern in advance not to loose identifiability and latency because of the gamma correction using the gamma correction apparatus 204. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  According to the present invention, an image is formed by performing image processing based on an input image signal, and a tracking (identification) pattern is formed on a copy to specify an apparatus used for copying, and to output a security document or the like. The present invention relates to an image processing apparatus for preventing illegal copying.

  In recent years, with the color copying of copiers, securities that should not be copied can be copied with high image quality that can hardly be distinguished from the original, which is why color copiers are abused. The risk has arisen. For this reason, various techniques for preventing or suppressing illegal copying of a copy-inhibited document have been considered. For example, the technology described in Japanese Patent Application Laid-Open No. 4-294682 is a tracking pattern on a copy, which is difficult to identify with the naked eye but can be read (potentially) using a scanner or the like. This is a technique for forming a (identifiable) tracking pattern indicating some information for specifying a copying apparatus. According to this technique, even when a copy-inhibited document is copied, it is possible to obtain a clue for specifying an apparatus used for copying.

  On the other hand, in an image processing apparatus such as a color copying machine, it is necessary to maintain the density characteristics of each primary color in order to secure a good color balance, and various techniques are known for this purpose. For example, the techniques described in Patent Literature 1 and Patent Literature 2 disclose a toner patch (a toner image of a primary color having a predetermined target density in an ideal state) on a photoreceptor or a transfer body for each primary color. The density of each of these toner patches is measured by a density sensor to determine a deviation between the measured density and a target value. This is a technique for obtaining an image with a high density. According to this technique, it is possible to maintain a good color balance without being affected by variations in the production of toner used for copying and changes over time in optical characteristics of a copying machine.

There is also a combination of a technique for forming the tracking pattern on a copy and a technique for controlling density characteristics using a toner patch. That is, a technique is also known in which a data signal for forming a tracking pattern is added (combined) to image data, and gamma correction is performed on the combined data signal according to each density of a toner patch.
JP-A-63-106672 JP-A-63-113568

  However, in such a combined technique, although an image having a desired density can be certainly obtained by the density correction according to the toner patch, as a result of the density correction, the tracking pattern is excessively corrected. It may be possible. In this case, the tracking pattern has a desired density when viewed macroscopically, but when viewed microscopically, the dots constituting the tracking pattern become too small, and a reading device such as a scanner is used. Even so, it is no longer possible to read, or conversely, the dots forming the tracking pattern become too large and the tracking pattern becomes identifiable with the naked eye. In any case, in such a case, there is a problem in that the tracking pattern loses one of the two characteristics of discrimination and latentness, and as a result, does not function as the tracking pattern.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and an object of the present invention is to make it difficult to identify a tracking pattern with the naked eye even when the density of a print image to be formed fluctuates. It is another object of the present invention to provide an image processing apparatus which can be identified.

  In order to solve the above-described problem, the present invention provides a generation unit that generates a tracking pattern signal for forming a tracking recording pattern, and forms a toner patch based on a toner patch signal corresponding to a predetermined toner density. Toner patch forming means, a toner density sensor for measuring the density of the toner patch formed by the toner patch forming means, a toner patch density measured by the toner density sensor, and a predetermined toner patch density Recognition means for recognizing a difference from the target value, and the toner patch so that the shape of the tracking recording pattern has a shape corresponding to the density value difference based on the density difference recognized by the recognition means. Correction means for correcting the tracking pattern signal independently of the signal; and a tracking pattern signal and a correction signal corrected by the correction means. To provide an image processing apparatus characterized by comprising a forming means for forming a recorded image on the basis of the fine the toner patch signal.

  The correction means may correct the tracking pattern signal so that the number of dots forming the tracking recording pattern is changed.

  Further, the correction means may correct the tracking pattern signal so that the size of the tracking recording pattern is changed.

  Further, the correction means may correct the tracking pattern signal so that the area of the dots constituting the tracking recording pattern is changed.

  The correction means may use a density deviation average value as the density difference.

1: Configuration of Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of a full-color copying machine incorporating the image processing apparatus of this embodiment. As shown in this figure, this full-color copying machine includes a scanner unit 100, an image processing unit 200, a ROS optical system 300, and an image forming unit 400. First, in the scanner unit 100, the exposure lamp 102 irradiates the document 109, the CCD 103 reads the reflected light, and the amplifier 104 amplifies the output to an appropriate level. The output of the amplifier 104 is converted into digital image data by an A / D converter 105, shading-corrected by a shading correction unit 106, and gap-corrected by a gap correction unit 107. The data is converted into data and supplied to the image processing unit 200. That is, the scanner unit 100 reads the document 109 and outputs the content as density data L ^* , a ^* , and b ^* .

Next, inside the image processing unit 200, reference numeral 201 denotes a color conversion unit, which converts the density data L ^* , a ^* , and b ^* into image data expressed by the density of the primary color YMCK. The image data is output for each page in the order of Y, M, C, and K. Reference numeral 202 denotes a gamma correction circuit that corrects each color gradation according to the gradation of the image forming unit 400. Reference numeral 203 denotes a tracking pattern adding circuit which adds a tracking pattern to image data whose color gradation has been corrected. A gamma correction circuit 204 performs gamma correction on the image data to which the tracking pattern has been added, and outputs the image data. Note that the tracking pattern adding circuit 203 and the gamma correction circuit 204 are independently controlled by a measured density of a toner patch described below under the control of the arithmetic unit 411. The size and area of the dots forming the tracking pattern are controlled, and the gamma correction circuit 204 controls the selection of a lookup table used for gamma correction. The details will be described in detail.

  A D / A converter 205 converts the gamma-corrected image data into an analog signal and outputs the analog signal. A triangular wave generator 206 outputs a triangular wave having a predetermined period. Reference numeral 207 denotes a triangular wave adjusting circuit that appropriately adjusts the level of the triangular wave and outputs the adjusted level. Reference numeral 208 denotes a comparator which compares the level of the analog signal output from the D / A converter 205 with the level of the triangular wave output from the triangular wave adjustment circuit 207. A "0" signal is output, otherwise a "1" signal is output. Therefore, the output signal of the comparator 208 is a pulse signal that becomes “1” or “0” as appropriate. The duty ratio of such a pulse signal decreases as the level of the analog signal increases, that is, as the density increases.

  Next, reference numeral 209 denotes a toner patch signal generation circuit which supplies an analog signal (toner patch signal) having a level corresponding to a predetermined toner density to the comparator 208 at a timing corresponding to the developing position of the toner patch. This analog signal is compared with the triangular wave from the triangular wave adjustment circuit 207 like the analog signal output from the D / A converter 205, and a pulse signal corresponding to the result is output from the comparator 208.

  Reference numeral 301 in the ROS optical system 300 denotes a laser driving circuit, which controls on / off of the laser 302 in synchronization with a pulse signal output from the comparator 208. That is, the laser 302 is turned on when the pulse signal is “1”, and is turned off when the pulse signal is “0”. The laser light amount is variable by a laser light amount varying device 306 controlled by the arithmetic unit 400. Then, the laser light emitted from the laser 302 is converged through the polygon 303, the fθ lens 304, and the reflection mirror 305 sequentially.

  On the other hand, an arithmetic unit 411 inside the image forming unit 400 controls other components based on a control program. A charging device 402 uniformly negatively charges the photoconductor 401 under the control of the arithmetic device 411 and the charge amount varying device 409. The photoconductor 401 rotates clockwise in FIG. 1 and emits the laser light after being charged by the charging device 402. As a result, a latent image is formed on the photoconductor 401. Reference numeral 403 denotes a rotary developing device for attaching toners of respective primary colors to the photoconductor 401. A toner dispensing device 412 supplies toner of each color to the rotary developing device 403 under the control of the arithmetic device 411. Here, the amount of toner supplied from the toner dispensing device 412 to the rotary developing device 403 is controlled by the arithmetic device 411 based on the measurement result of the toner density sensor 414, and the developing bias is controlled by the arithmetic device 411. It is changed by the bias varying device 416.

  Reference numeral 406 denotes a transfer device that transfers the toner attached to the photoconductor 401 onto copy paper. Reference numeral 404 denotes a cleaner device that removes toner remaining on the photoconductor 401. Reference numeral 405 denotes a neutralization lamp, which neutralizes the photoconductor 401. Reference numeral 410 denotes an electrometer, which measures the potential of the photoconductor 401 charged by the charging device 402. A humidity sensor 413 measures the humidity around the photoconductor 401. A toner density sensor 414 measures the density of the toner developed on the photoconductor 401. Then, the measurement results of the electrometer 410 and the sensors 413 and 414 are supplied to the arithmetic unit 411.

1-1: Gamma Correction Here, gamma correction performed in this embodiment will be described. First, the density of each primary color YMCK in the image data of this embodiment is represented by 256 gradations of 8 bits (“0” to “255”). However, if an image is simply formed based on such image data, the fidelity is impaired when the density characteristics and the like of the image forming unit 400 fluctuate. Therefore, the image data is corrected by the gamma correction circuit 202 in accordance with the density characteristics of the image forming unit 400, and then the image data to which the tracking pattern is added is converted by the gamma correction circuit 204 into the density of the image forming unit 400. Correction is appropriately made in accordance with variations in characteristics and the like. That is, the gamma correction by the gamma correction circuit 202 is fixedly performed according to the density characteristics of the image forming unit 400, but the gamma correction by the gamma correction circuit 204 is variably performed according to the fluctuation of the density characteristics. ing.

  Therefore, the gamma correction circuit 204 is provided with seven types of lookup tables LUT_1 to LUT_7. FIG. 2 shows input / output characteristics corresponding to these LUT_1 to LUT_7. As illustrated, when any one of LUT_1 to LUT_3 is selected, the density of the image data before conversion is higher than that of the image data after conversion. On the other hand, when any one of LUT_5 to LUT_7 is selected, the density of the image data before conversion is lower than that of the image data after conversion. When LUT_4 is selected, the densities of the image data before and after the conversion become equal. Then, one of them is selected according to the deviation between the density value of the toner patch detected by the toner density sensor 414 and the target value. More specifically, if there is almost no deviation, LUT_4 is selected. If the density value of the toner patch is higher than the target value and the toner patch is dark, LUT_7, LUT_6, and LUT_5 are arranged in the order of the density (deviation). If the density value of the toner patch is lower than the target value and the toner patch is thin, one of LUT_1, LUT_2, and LUT_3 is selected in the order of the thinness (deviation). It has become. Then, the input / output characteristics of the gamma correction circuit 204 are determined according to the selected look-up table.

1-2: Tracking Pattern Next, a tracking pattern will be described.
FIG. 3 is a plan view showing the copy sheet 30 on which the tracking pattern is formed. As shown in this figure, a large number of tracking patterns are recorded in recording areas 31, 31... This is to prevent the partial abuse of the copy, and even if a copy that is not to be copied and has a very small area, such as a stamp, is copied, the tracking pattern is printed on the copy. Is formed. Next, focusing on a recording area 31 in which one tracking pattern is recorded, as shown in FIG. 4, the tracking pattern is composed of dot areas 32 having a plurality of small rectangles. . By the arrangement of these dot areas 32, 32,..., Information unique to the color copying machine is shown by being coded or the like by a predetermined method. By decoding this, the color copying machine used for copying can be specified. Focusing on one dot area 32, the dot area 32 is composed of pixels 33, 33,... Of n rows in the sub-scanning direction and m columns in the main scanning direction, as shown in FIG.

  In general (including this embodiment), a color copying machine forms a color image by synthesizing four colors of yellow, magenta, cyan and black. The dot areas 32, 32,... Are printed in a combination of a plurality of colors. As such a specific color, a single color of yellow, which is difficult to identify with the naked eye, is preferable.

1-3: Tracking Pattern Adding Circuit Next, a tracking pattern adding circuit 203 for adding such a tracking pattern to an input image will be described.
FIG. 6 is a block diagram showing the configuration of the tracking pattern adding circuit 203. In this figure, reference numeral 51 denotes a buffer memory, which stores image data output from the gamma correction circuit 202 in FIG. That is, the buffer memory 51 stores image data of the document 109 read by the CCD 103 and subjected to various corrections. Reference numeral 52 denotes a selector, which receives image data read from the buffer memory 51 via an input terminal A, receives predetermined color data via an input terminal B, and supplies the binary data supplied to a selected input terminal SEL. Either data is output based on the signal. That is, when a "0" signal is supplied to the selection input terminal SEL, the input terminal A is selected, and when a "1" signal is supplied, the input terminal B is selected. The correction signal is supplied to the correction circuit 204. Reference numeral 60 denotes a CPU, which controls other components by communication with the arithmetic unit 411 based on a control program stored in the ROM 61. A RAM 62 temporarily stores various data by the CPU 60 via the bus 63. Registers 64 to 67 store data as described below and output the data under the control of the CPU 60.

  First, the register 64 is written with the coordinate conditions of the recording area 31 where the tracking pattern is to be recorded on the copy sheet 30. In detail, the tracking pattern is provided on the copy paper 30 as shown in FIG. 3 and in the recording areas 31, 31,... If the coordinates satisfy a certain condition, this pixel is included in the recording area 31. That is, the coordinate conditions indicating the areas of the recording areas 31, 31,... Are written in the register 64.

  Returning to FIG. 6, a coordinate condition in a case where an arbitrary pixel in the recording areas 31, 31,... Belongs to the dot areas 32, 32,. Here, if the content of the register 65 is appropriately rewritten under the control of the CPU 60 so as to increase or decrease the number of pixels (see FIG. 5) constituting the dot area 32 in the main scanning direction, the area of the dot constituting the tracking pattern Can be changed.

  On the other hand, the register 66 stores a condition as to whether or not to print the tracking pattern as 1-bit data of “1” or “0”. That is, when the tracking pattern is to be printed on the copy sheet 30, "1" is written in the register 66, and when it is not to be printed, "0" is written. In a normal use state, "1" is always written to the register 66 to prevent abuse.

  By the way, in FIG. 5, the width (length in the sub-scanning direction) of each dot area 32, 32,... Is set to a predetermined value b. However, in this embodiment, the width of the dot regions 32, 32,... Is set to twice (2b) under the control of the CPU 60 under certain conditions. The register 67 stores the condition as 1-bit data. When the content is “0”, the width of the dot areas 32, 32,... Is designated to be “b”. If it is "1", it specifies that the width should be "2b". As a result, the number of dots forming the tracking pattern changes. The register 68 stores colors to be printed in the dot areas 32, 32,... As color data, and supplies the color data to the input terminal B of the selector 52. In this embodiment, the color data set in the register 68 by the CPU 60 is normally yellow.

  Next, a clock circuit 70 outputs a video clock signal V_CK, a line sync signal L_SYNC, and a page sync signal P_SYNC described below under the control of the CPU 60 via the bus 63. First, the video clock signal V_CK is a clock signal that determines the timing at which each pixel is output in the main scanning direction. The line sync signal L_SYNC is a signal that determines the timing at which each pixel is output in the sub-scanning direction, and has a cycle that is about several thousand times the video clock signal V_CK. The page sync signal P_SYNC is a signal that determines the timing at which printing of one page of the copy sheet 30 ends, and has a cycle that is about several thousand times the line sync signal L_SYNC.

  A counter 71 counts the video clock signal V_CK and supplies the result to the buffer memory 51 as an address signal. The counting result is reset to “0” by the page sync signal P_SYNC. A counter 72 counts the video clock signal V_CK, outputs the result, and resets the count result to “0” by the line sync signal L_SYNC. A counter 73 counts the line sync signal L_SYNC and outputs the result, and the counting result is reset to “0” by the page sync signal P_SYNC. Therefore, the counting result of the counter 72 corresponds to the coordinates in the main scanning direction, and the counting result of the counter 73 corresponds to the coordinates in the sub-scanning direction.

  A determination circuit 74 determines whether or not the coordinates specified by the counting results of the counters 72 and 73 match the coordinate conditions of the recording area stored in the register 64. When the determination circuit 74 determines that “match”, it outputs a “1” signal to the AND circuit 75. Reference numerals 76 and 77 denote counters, and reference numeral 78 denotes a determination circuit, which has the same configuration as the above-described counters 72 and 73 and determination circuit 74. The determination circuit 78 determines whether the coordinates specified by the counting results of the counters 76 and 77 match the coordinate conditions of the dot area stored in the register 65. When the determination circuit 77 determines “match”, it outputs a “1” signal to the AND circuit 75.

  The AND circuit 75 outputs a “1” signal when the “1” signal is output from each of the determination circuits 74 and 78 and the register 66. A delay circuit 79 delays the output signal of the AND circuit 75 by a predetermined time and outputs the delayed signal. This delay time is n times (n is the number of dots in the sub-scanning direction of the dot area 32 in FIG. 5) the cycle of the line sync signal L_SYNC. An OR circuit 80 outputs a logical sum of output signals of the delay circuit 79 and the AND circuit 75. A selector 50 receives output signals of the AND circuit 75 and the OR circuit 80 at input terminals A and B, respectively. The selector 50 receives the output signal of the register 67 at the selection input terminal SEL, and selects the output signal of the AND circuit 75 when the output signal is “0”, and selects the output signal of the AND circuit 75 when the output signal is “1”. And outputs the selected signal. Then, the output signal of the selector 50 is supplied to the selection input terminal SEL of the selector 52.

  Note that the tracking pattern is output by being superimposed on the image data by the selector 52. The superimposition of the tracking pattern is performed only in the image forming cycle of the primary color corresponding to the color data set in the register 68. Done.

2: Operation of Embodiment Next, the operation of the embodiment having the above-described configuration will be described.
2-1: Formation and Density Measurement of Toner Patch First, when the power is turned on to the color copying machine of this embodiment, the toner patch of each primary color (YMCK) is placed at a predetermined position on the photoconductor 401 in the following manner. Is formed, and the concentration measurement result is stored.

  First, when a portion where a toner patch is to be formed on the photoconductor 401 faces the charging device 402, this portion is charged. Next, a command to generate a toner patch signal is transmitted from the arithmetic device 411 to the toner patch signal generation circuit 209. As a result, the toner patch signal is supplied from the toner patch signal generation circuit 209 to the comparator 208 for a predetermined period. On the other hand, a triangular wave is supplied from the triangular wave generator 206 to the comparator 208 via the triangular wave adjusting circuit 207, and a pulse signal is supplied from the comparator 208 to the laser driving circuit 301 based on the magnitude relationship between the toner patch signal and the triangular wave. You. As a result, pulsed laser light is emitted from the laser 302, and the laser light forms a latent image of a toner patch on the photoconductor 401 via the polygon 303 to the reflection mirror 305.

  Next, after the latent image of the toner patch is generated on the photoconductor 401, when the photoconductor 401 is slightly rotated, the previously formed latent image faces the rotary developing device 403. As a result, toner of a predetermined color (any one of YMC) is attached to the charged portion on the photoconductor 401, and the toner patch is developed. When the photoconductor 401 further rotates and the toner patch faces the toner density sensor 414, the density of the toner patch is measured by the toner density sensor 414, and the result is stored in the arithmetic unit 411. When the photoconductor 401 further rotates, the toner of the toner patch is removed by the cleaner device 404, the charge of the toner patch portion of the photoconductor 401 is removed by the discharging lamp 405, and then the photoconductor 401 is charged again by the charging device 402. The above operation is performed for each primary color of YMC, and the arithmetic unit 411 stores the density measurement result for each primary color of YMC.

2-2: Selection of Look-Up Table Next, when the density of the toner patch is measured for each color, a target value is subtracted from the measured value of the density of the toner patch for each primary color YMC. (Average density deviation) is obtained. Note that the target value of the density of each toner patch is stored in the arithmetic unit 411 in advance. Then, as described above, the look-up table in the gamma correction circuit 204 is selected according to the density deviation average value, and the input / output characteristics of the gamma correction are determined.

2-3: Setting of Tracking Pattern On the other hand, when the density of the toner patch is measured, the tracking pattern to be added to the image is changed by the tracking pattern adding device 203 independently of the selection of the lookup table. . In this embodiment, what is changed is the number of dots and the area of the dot region 32 forming the tracking pattern. Note that the arrangement of the dot areas 32 is not changed. This is because the information to be tracked is indicated by this array. Further, the tracking pattern is changed here in order to prevent the tracking pattern from losing the discriminability and the potential by the gamma correction in the later stage. In this embodiment, the arrangement of the dot regions 32 is changed. Three types of tracking patterns A, B, and C that are the same (that is, the information indicated by the tracking patterns are the same) are prepared, and one of them is selected based on the average value of the density deviation and added to the image data. It has become.

  This selection is performed as follows. That is, when the average deviation value obtained by subtracting the measured density value of the toner patch from the target value is “6” or more, that is, when the density of the toner patch is somewhat lower than the target density, the tracking pattern A is Selected. If the average deviation value is “-5” or less and “−5”, that is, if the density of the toner patch falls within a predetermined range with respect to the target density, the tracking pattern B is selected. On the other hand, when the average deviation value is equal to or smaller than “−6”, that is, when the measured density of the toner patch is somewhat higher than the target density, the tracking pattern C is selected.

  Here, the relationship between the tracking patterns A, B, and C and the original tracking patterns will be described with reference to FIGS. As shown in FIG. 7, the tracking pattern A is obtained by doubling the dot area 32 constituting the original tracking pattern in the sub-scanning direction to two dots, and the toner of the color copying machine becomes thin for some reason. It is a measure for the state that was left. That is, since the toner is thin, the gamma correction for increasing the density is performed, and as a result, the area of the dot region 32 forming the tracking pattern is increased. However, since the toner itself is thin, the tracking pattern has poor discrimination. There is a possibility that it cannot be read by a scanner or the like. For this reason, correction for increasing the density of the tracking pattern is performed in advance. When the tracking pattern A is selected, in the tracking pattern adding circuit 203, “1” is written into the register 67, and the length of the dot area 32 in the sub-scanning direction is doubled to 2 It is changed to be composed of dots.

  The tracking pattern B is the same as the original tracking pattern as shown in FIG. This is because since the toner of the color copying machine is normal, the gamma correction circuit 204 only performs gamma correction on the image data to which the tracking pattern has been added, so that the tracking pattern can exhibit discrimination and potential. It is.

  As shown in FIG. 9, the tracking pattern C has a dot area 32 constituting the original tracking pattern with an area of about 70%, and measures for a state in which the toner of the color copying machine becomes dark for some reason. It is. That is, since the density of the toner is high, gamma correction is performed to reduce the density, and as a result, the area of the dot region 32 forming the tracking pattern is also reduced. However, the density of the toner itself still increases the potential of the tracking pattern. It may not be able to demonstrate and may be discerned with the naked eye. For this reason, correction is performed in advance to reduce the density of the tracking pattern. When the tracking pattern C is selected, in the tracking pattern adding circuit 203, the contents of the register 65 are rewritten, and the coordinate conditions of the dot area 32 are changed. However, in this case, if the area of the dot region 32 is excessively reduced, the dot region 32 becomes too small, and may not be read by a scanner or the like. Therefore, the CPU 60 performs control so that the area of the dot region 32 does not become smaller than the resolution of the reading device.

  When the density of the toner patch is measured in this way, a look-up table that determines the input / output characteristics of the gamma correction by the gamma correction circuit 204 is selected, and the look-up table is superimposed on the image data in the tracking pattern adding circuit 203. A tracking pattern is determined. The tracking pattern is actually added to the image data, the gamma correction is performed, and the image formation based on the corrected image data is performed after the operation of copying the original is performed. is there. Therefore, an operation when such a copying operation is performed will be described below.

2-4: Reading of Original First, when a predetermined operation indicating that the original is to be copied is performed, the original is read by the scanner unit 100, and the content is output as density data L ^* , a ^* , b ^*. Are output from the color conversion unit 201 in the order of Y, M, C, and K for each page. This image data is density-corrected by the gamma correction circuit 202 in accordance with the density characteristics of the image forming unit 400. The density-corrected image data is supplied to the tracking pattern adding circuit 203.

2-5: Operation of Tracking Pattern Addition Circuit Next, the gamma-corrected image data is temporarily stored in the buffer memory 51 (see FIG. 6) in the tracking pattern addition circuit 203. Then, when the image data is stored in the buffer memory 51, an output process is performed. That is, a control signal is supplied from the CPU 60 to the clock circuit 70, and the clock circuit 70 enters an operating state. When the clock circuit 70 operates, the clock circuit 70 outputs a video clock signal V_CK, a line sync signal L_SYNC, and a page sync signal P_SYNC. Other components are driven by these signals, but the operation differs depending on the case where the tracking pattern A or B or C is selected.

2-5-1: When the tracking pattern B or C is selected In this case, "0" is set in the register 67 so that the dot areas 32, 32,... Set. Therefore, in the selector 50, the output signal of the AND circuit 75 is selected. The counter 71 counts the video clock signal V_CK and supplies the result to the buffer memory 51 as an address signal. Therefore, image data for each pixel is sequentially supplied to the input terminal A of the selector 52. Here, when the coordinates specified by the count results of the counters 72 and 73 do not match the coordinate conditions of the recording area, or when the coordinates specified by the count results of the counters 76 and 77 do not match the coordinate conditions of the dot area, , AND circuit 75 outputs a “0” signal. Since the “0” signal is supplied to the selection input terminal SEL of the selector 52 as it is via the input terminal A of the selector 50, the image data stored in the buffer memory 51 is supplied to the gamma correction circuit 204. On the other hand, when each of the coordinates corresponds to the coordinate condition of the recording area and the coordinate condition of the dot area, the AND circuit 75 outputs a “1” signal. When this “1” signal is supplied to the selection input terminal SEL of the selector 52 via the selector 50, the color data (yellow) stored in the register 68 is supplied to the gamma correction circuit 204 via the input terminal B. You. As a result, the print color of each dot area 32, 32,... On the copy paper 30 becomes yellow based on the color data. When the pattern C is selected, the coordinate conditions set in the register 65 are changed so that the lengths of the dot areas 32, 32,... Are each 70% in the main scanning direction.

2-5-2: When Tracking Pattern A is Selected In this case, "1" is set in the register 67 so that the dot areas 32, 32,... Constituting the tracking pattern are composed of two dots. You. Therefore, in the selector 50, the output signal of the OR circuit 80 is selected. In this case, the “1” signal output from the AND circuit 75 is supplied to the selection input terminal SEL of the selector 52 via the OR circuit 80 and the input terminal B of the selector 50 in order. Therefore, the print colors of the dot areas 32, 32,... On the copy paper 30 are yellow as in the case described above. Further, the “1” signal output from the AND circuit 75 is supplied to the selection input terminal SEL of the selector 52 via the OR circuit 80 and the selector 50 after being delayed via the delay circuit 79. Since this delay time is n times the cycle of the line sync signal L_SYNC, the print color of the area adjacent to each dot area 32 and having the same shape as the dot area (hereinafter referred to as an extended area) is set to yellow. You. FIG. 5 shows an extended area 34 adjacent to the dot area 32.

  In this manner, in the tracking pattern adding circuit 203, the data of the tracking patterns A, B, and C are superimposed on the image data and supplied to the gamma correction circuit 204 according to the average value of the density deviation due to the toner patch. You.

2-6: Gamma Correction When the image data to which the tracking pattern data has been added by the tracking pattern adding circuit 203 is supplied to the gamma correction circuit 204, the image data is obtained according to the look-up table selected by measuring the density of the toner patch. The image data is converted. Here, the shape of the tracking pattern is corrected in advance by the tracking pattern adding circuit 203 so that the discriminability and the potential are not lost by the gamma correction. The disadvantage that the use pattern can be identified with the naked eye or cannot be read even with a scanner is avoided.

2-7: Image Formation When the image data is subjected to density conversion by the gamma correction circuit 204, an image is formed on the copy paper 30 in accordance with the converted image data. That is, the laser drive circuit 301 is driven based on the converted image data, and the latent image processing and the development processing are performed on the photoconductor 401. On the other hand, the copy sheet is transported to the transfer device 406, and the developed toner is transferred to the copy sheet. Such latent image, development and transfer processes are performed for each primary color, and each toner is transferred to copy paper. Thereafter, each toner is fixed on the copy sheet, and the copy sheet is discharged.

3: Modification In the above-described embodiment, the tracking pattern is corrected according to the density deviation of the toner patch. The content of the correction changes the area of the dot region 32 and the number of dots forming the tracking pattern. Was to do. However, the present invention is not limited to the above-described technique, and may be of any type as long as the density of the tracking pattern is changed. For example, the following various modifications may be given.

  The color of the dot area 32 forming the tracking pattern is changed. When the toner patch is thin, as shown in FIG. 10, the color of the dot area 32 is changed from yellow to cyan or the like, and correction is performed so as to increase the density of the tracking pattern. In this case, the CPU 60 in FIG. 6 sets cyan color data in the register 68, and when the cyan (C) image data is supplied, a tracking pattern may be added.

  Change the interval of the tracking pattern. When the toner patch is dark, as shown in FIG. 11, the interval a of the tracking pattern (recording area 31) is increased to make the interval a ', so that the tracking pattern is corrected to be thin. Conversely, when the toner patch is thin, the interval between the tracking patterns is narrowed, and the correction is performed so that the tracking patterns are darkened. In this case, the CPU 60 changes the coordinate condition of the recording area 31 in the register 64. However, in this case, if the interval between the recording areas 31 is unlimitedly widened, the trace pattern is not included in a small-sized copy such as a stamp, and partial abuse of the copy may not be prevented. . Therefore, the CPU 60 performs control so that the interval between the recording areas 31 does not exceed a predetermined value so that at least one tracking pattern is formed in such a small area.

  The interval between the dot regions 32 forming the tracking pattern is changed. When the toner patch is dark, as shown in FIG. 12, the intervals between the dot areas 32, 32,... Are increased so that the areas of the recording areas 31, 31,. That is, the correction is performed so that the tracking pattern itself is enlarged. On the other hand, when the toner patch is thin, the interval between the dot areas 32, 32,... Is corrected so that the area of the recording areas 31, 31,. That is, the correction is performed so as to reduce the tracking pattern itself. However, if the tracking pattern itself is increased indefinitely, there is a possibility that an adjacent tracking pattern may be overlapped. Therefore, the correction is made so that the interval between the recording areas 31 is also increased. Further, when the interval between the recording areas 31 is increased, it is necessary to make correction so as not to exceed a predetermined value for the above-described reason. In consideration of these, the CPU 60 rewrites the contents of the register 64 together with the register 65, and changes the coordinate condition of the recording area on the copy sheet 30 as well as the coordinate condition of the dot area 32 in the recording area 31.

4: Others In the above-described embodiment or modified example, when correcting the tracking pattern, the number of dots, the area, the color, the interval of the dot area 32 constituting the tracking pattern, or the size of the tracking pattern itself are independently determined. Although these elements are changed, a plurality of these elements may be arbitrarily combined and changed according to the average value of the density deviation of the toner patch.

FIG. 1 is a block diagram showing a configuration of an embodiment according to the present invention. 3 is a diagram illustrating characteristics of a lookup table used for gamma correction according to the embodiment. FIG. 3 is a plan view showing a configuration of a copy sheet in the embodiment. FIG. 3 is a plan view illustrating a configuration of one of tracking patterns printed on the copy sheet. FIG. 3 is a plan view showing a configuration of one of dot areas in the tracking pattern. FIG. 3 is a block diagram illustrating a configuration of a tracking pattern adding circuit in the same embodiment. FIG. 9 is a diagram illustrating an example of the content of correction in the tracking pattern adding circuit. FIG. 9 is a diagram illustrating an example of the content of correction in the tracking pattern adding circuit. FIG. 9 is a diagram illustrating an example of the content of correction in the tracking pattern adding circuit. FIG. 9 is a diagram illustrating an example of the content of correction in the tracking pattern adding circuit. FIG. 9 is a diagram illustrating an example of the content of correction in the tracking pattern adding circuit. FIG. 9 is a diagram illustrating an example of the content of correction in the tracking pattern adding circuit.

Explanation of reference numerals

203: tracking pattern adding circuit (generating means) 400: image forming unit (forming means) 411: arithmetic unit (recognizing means)

Claims (5)

Generating means for generating a tracking pattern signal for forming a tracking recording pattern;
Toner patch forming means for forming a toner patch based on a toner patch signal corresponding to a predetermined toner density;
A toner density sensor that measures the density of the toner patch formed by the toner patch forming unit;
Recognition means for recognizing a difference between the density of the toner patch measured by the toner density sensor and a predetermined target value of the density of the toner patch;
The correction of the tracking pattern signal is performed independently of the toner patch signal such that the shape of the tracking recording pattern has a shape corresponding to the density value difference based on the density difference recognized by the recognition unit. Correction means for performing;
An image processing apparatus comprising: a forming unit that forms a recorded image based on the tracking pattern signal corrected by the correcting unit and the toner patch signal.   The image processing apparatus according to claim 1, wherein the correction unit corrects the tracking pattern signal so that the number of dots forming the tracking recording pattern is changed.   2. The image processing apparatus according to claim 1, wherein the correction unit corrects the tracking pattern signal so that the size of the tracking recording pattern is changed.   The image processing apparatus according to claim 1, wherein the correction unit corrects the tracking pattern signal such that an area of a dot forming the tracking recording pattern is changed.   2. The image processing apparatus according to claim 1, wherein the correction unit uses an average value of a density deviation as the density difference.

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