JP3816398B2 - Image processing method, image processing apparatus, and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing method for adding specific information to an image to be formed, an image processing apparatus, and an image forming apparatus provided with the image processing apparatus in a color image forming apparatus such as a copying machine, a facsimile machine, and a printer. .
[0002]
[Prior art]
Some image forming apparatuses such as digital color copying machines that form multicolor images can perform full-color copying. In recent years, such digital color copiers have been put into practical use that can obtain copies with high image quality that are indistinguishable from originals. For this reason, there is a risk that banknotes and securities that are prohibited from being copied are copied for counterfeit purposes.
[0003]
Therefore, in the unlikely event that counterfeiting is performed, tracking information such as the manufacturer of the device that produced the copy, the serial number, and the date the copy was copied, etc. can be tracked and identified. In addition, a technique for adding a tracking pattern image obtained by encrypting tracking information to a copy image at the time of copying has been developed. By reading a copy generated by this technique with a tracking pattern image reading device (hereinafter referred to as “reading device”), the added tracking pattern can be read to obtain tracking information.
[0004]
This tracking pattern image is not selectively added, but is added to all color copy images. Therefore, the tracking pattern image is formed using, for example, a yellow color material that is difficult to visually recognize, so that the tracking pattern image does not cause noise and deteriorate the image quality of the copy.
[0005]
Further, if this tracking pattern image is added in the same way at any position of the copy image regardless of the density of the copy image, for example, it may be difficult to read with a reading device in a high density region or a low density region. .
[0006]
[Problems to be solved by the invention]
For this reason, in the technique disclosed in Japanese Patent No. 312590, the density of the tracking pattern image to be added is changed in accordance with the density of the image data of the original to make it easy to read the tracking pattern image. Specifically, when the density of the image data of the document is equal to or lower than a specific density, the tracking pattern image is added so that the density becomes readable by the reading device. If the density of the image data of the document exceeds a specific density, the tracking pattern image is added by adding a certain density to the image data so that the density of the tracking pattern image is higher than the actual image density. Yes.
[0007]
However, in the technique disclosed in Japanese Patent No. 312590, addition cannot be performed when the actual image density is the maximum density, and thus the trace pattern image also has the same density as the actual image density. . For this reason, there is a problem that the tracking pattern image cannot be recognized in the region of the document having the maximum image density.
[0008]
In the technique disclosed in Japanese Patent Laid-Open No. 8-88757, the method for adding a tracking pattern image is changed according to the image density. However, in the tracking pattern image addition processing by this method, the density of the tracking pattern image after processing may be 0 density. This causes a problem that the difference from the actual image density becomes too large and becomes conspicuous.
[0009]
The present invention has been made to solve the above problems. The purpose of the tracking pattern is that it is less visible to the human eye regardless of the density of the image data of the document and can be read well by the tracking pattern image reading apparatus. An image processing method for adding an image, an image processing apparatus, and an image forming apparatus including the image processing apparatus are provided.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, an image processing method of the present invention performs density conversion on image data indicating an image of a document in order to add a tracking pattern image to the image of the document. Determining whether the density indicated by the image data to which the image is to be added belongs to at least one of a low density area, a middle density area, and a high density area; and the density indicated by the image data is a low density area or a medium density If the image data belongs to a high density area, the density of the image data is converted to a higher density side than the density by a method different for each density area. If the density indicated by the image data belongs to the high density area, the image data And a step of converting the density of the data to a lower density side than the density.
[0011]
This image processing method is used in an image forming apparatus having a function of adding a tracking pattern image to a copy based on tracking information data so that a copy or the like obtained by image formation can be traced later.
[0012]
In the image processing method of the present invention, it is determined whether the density of the input document image data belongs to at least one of the low density area, medium density area, and high density area. Thereafter, a tracking pattern image is added by performing density conversion for each of the three different density areas by different methods.
[0013]
In the present invention, adding a tracking pattern image means performing density conversion on a specific part of the original image data in order to give information for tracking investigation to a copy or the like. That is, the tracking pattern image can be added by converting the density of the original image data to a density higher or lower than the density.
[0014]
The tracking pattern image is added to all copies and the like. For this reason, it is preferable that the addition of the tracking pattern image is recognized accurately by the reading device, but conversely, if the easiness to recognize is excessively determined, the tracking pattern image becomes visually noise and the image quality is degraded. .
[0015]
Therefore, according to the above method, by dividing the image data of the document into the above three types of areas according to the density, it is possible to add the tracking pattern image by a method suitable for each density area. Thereby, the tracking pattern image can be satisfactorily read in the entire density range, and the tracking pattern image can be made inconspicuous.
[0016]
Specifically, in the low density region and the middle density region, the density of the image data is increased by converting the density to a higher density side than the density of the image data. Here, density conversion is performed by a method different from that for the middle density area, taking into consideration difficulty in reading the tracking pattern image and conspicuousness especially in the low density area. As a result, the tracking pattern image can be satisfactorily read even in the low density region, and the tracking pattern image can be made inconspicuous.
[0017]
In the high density range, the density of the image data is lowered by converting the density to a lower density side than the density of the image data. As a result, the image data after density conversion, which may occur when the density of the image data is converted to the high density side in the high density area, exceeds the maximum density in the image data, and the pixel to which the tracking pattern image is added And the problem that it becomes impossible to distinguish from other pixels not added.
[0018]
Therefore, according to the method described above, tracking is possible for the reading apparatus to perform good reading with low visibility to the human eye, regardless of the range of the image data density of the document. An image processing method for adding a pattern image can be provided.
[0019]
Further, the image processing apparatus of the present invention performs density conversion on image data indicating an image of a document in order to add a tracking pattern image to an image of the document, and an image to which the tracking pattern image is to be added. It is determined whether the density indicated by the data belongs to at least a low density area, a middle density area, or a high density area, and if the density indicated by the image data belongs to a low density area or a middle density area, the density If the density of the image data is converted to a higher density side than the density by a different method for each area, and the density indicated by the image data belongs to the high density area, the density of the image data is set lower than the density. A density conversion unit that converts density on the density side is provided.
[0020]
According to the above configuration, as with the image processing method described above, the human eye has low visibility regardless of the range of the density of the image data of the document, and good reading for the reading device. It is possible to provide an image processing apparatus that adds a tracking pattern image that can be performed.
[0021]
In the image processing method described above, the image data indicating the image of the document includes color image data of yellow (Y), magenta (M), and cyan (C) (the image data further includes black ( K) color image data may be included). The tracking pattern image is preferably added to the yellow color image data of the color image data.
[0022]
According to the above method, yellow has the lowest visibility among the above three (or four) colors, so if yellow color image data is used for adding tracking information, the effect on the image quality of the copied material is affected. Can be minimized.
[0023]
In the image processing apparatus, the same effect as that of the image processing method can be obtained. Therefore, it is preferable that the density conversion unit performs density conversion on yellow color image data.
[0024]
In the image processing method described above, when the density indicated by the image data belongs to a low density range, the density conversion is performed so that the density after density conversion is equal to or higher than the lowest density that can be recognized by a reading device that reads the tracking pattern image. It is preferable.
[0025]
According to the above method, the added tracking pattern image can be read for all image data in the low density region. That is, in the low density area, if the density of the original image data is low, there may occur a case where the reading apparatus cannot recognize the tracking pattern image by adding the density. However, if the tracking pattern image is added by the above method, all the tracking pattern images can be reliably read.
[0026]
Also, in the above image processing apparatus, the same effect as in the above image processing method can be obtained. Therefore, when the density indicated by the image data belongs to a low density range, the density conversion unit It is preferable to perform density conversion so that the density is equal to or higher than the lowest density that can be recognized by a reading device that reads the tracking pattern image.
[0027]
In the image processing method described above, when the density indicated by the image data belongs to a low density range, it is more preferable to perform density conversion so that the density conversion amount decreases as the density of the image data before density conversion increases.
[0028]
The tracking pattern image can be easily read by increasing the density conversion amount with respect to the density of the original image data. However, if the tracking pattern image is added with a density conversion amount that is too large relative to the density of the original image data, the tracking pattern image becomes visually conspicuous, and the image quality of a copy or the like deteriorates. Invite. Therefore, according to the above method, in the low density region, the density conversion amount becomes smaller as the density of the image data becomes higher. Therefore, it is possible to prevent the tracking pattern image from becoming visually noticeable. Therefore, it is possible to achieve both the formation of a reliable tracking pattern image that can be easily recognized by the reading device and the formation of a tracking pattern image that is visually inconspicuous.
[0029]
Also, in the above image processing apparatus, the same effect as the above image processing method can be obtained. Therefore, when the density indicated by the image data belongs to a low density range, the density conversion unit is the one before the density conversion. More preferably, the density conversion is performed so that the density conversion amount decreases as the density of the image data increases.
[0030]
In the above image processing method, when the density indicated by the image data belongs to a high density range, it is preferable that the density after density conversion is converted to a density higher than the lowest density that can be recognized by a reading device that reads the tracking pattern image. .
[0031]
According to the above method, it is possible to convert the density of image data in a high density range to a density within a range recognizable by the reading device. Thereby, a tracking pattern image can be recognized reliably.
[0032]
In the above image processing apparatus, the same effect as the above image processing method can be obtained. Therefore, when the density indicated by the image data belongs to a high density range, the density conversion unit It is preferable to convert the density so that the density is equal to or higher than the lowest density that can be recognized by a reading device that reads the tracking pattern image.
[0033]
In the above image processing method, when the density indicated by the image data belongs to a high density range, it is more preferable to perform density conversion so that the density conversion amount is constant.
[0034]
If the difference between the density of the original image data and the density after the density conversion process becomes larger than necessary, there arises a problem that the tracking pattern image becomes visually noticeable. According to the above method, it is possible to prevent a difference in density before and after density conversion from increasing, and to prevent the tracking pattern image from becoming visually noticeable in a high density region. Therefore, it is possible to achieve both the formation of a reliable tracking pattern image that can be easily recognized by the reading device and the formation of a tracking pattern image that is visually inconspicuous.
[0035]
In the above image processing apparatus, the same effect as the above image processing method can be obtained. Therefore, when the density indicated by the image data belongs to a high density range, the density conversion unit has a density conversion amount. It is more preferable to convert the density so as to be constant.
[0036]
In the image processing method described above, when the density indicated by the image data belongs to the middle density range, it is preferable to perform density conversion so that the density after density conversion is less than the highest density in the image data.
[0037]
According to the above method, after the tracking pattern image is added, all image data belonging to the middle density region is converted to a density less than the highest density in the image data. Therefore, it is possible to reliably add the density amount to be added, and the tracking pattern image can be easily recognized.
[0038]
In the above image processing apparatus, the same effect as the above image processing method can be obtained. Therefore, when the density indicated by the image data belongs to the middle density range, the density conversion unit More preferably, the density conversion is performed so that the density is less than the highest density in the image data.
[0039]
An image forming apparatus according to the present invention includes the above-described image processing apparatus and an image forming unit that forms an image based on image data whose density has been converted by the image processing apparatus.
[0040]
According to the above configuration, since the image forming apparatus includes the above-described image processing apparatus, the human eye has low visibility regardless of the density of the image data of the document. An image to which a tracking pattern image that can be read satisfactorily can be added to the reading device. Therefore, it is possible to easily and reliably recognize tracking information for all copies and the like, which is useful for preventing counterfeiting of banknotes and securities. In addition, copying can be performed on other copies without adversely affecting the image quality.
[0041]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
[0042]
FIG. 2 shows a configuration of a digital color copying machine 1 which is an image forming apparatus according to the present embodiment. A document table 111 and an operation panel (not shown) are provided on the upper surface of the digital color copying machine 1, and an image reading unit 110 and an image forming unit 210 are provided inside the digital color copying machine 1. A double-sided automatic document feeder (RADF) 112 is mounted on the upper surface of the document table 111. The double-sided automatic document feeder 112 is supported so as to be openable and closable with respect to the document table 111 and is provided at a predetermined position with respect to the surface of the document table 111.
[0043]
Further, the double-sided automatic document feeder 112 first transports the document such that one side of the document faces the image reading unit 110 at a predetermined position on the document table 111. After the reading of the image on one side is completed, the document is reversed and conveyed toward the document table 111 so that the other surface faces the image reading unit 110 at a predetermined position on the document table 111. It has become. The double-sided automatic document feeder 112 discharges the original after one-sided image reading for one original is completed, and executes a double-sided conveyance operation for the next original.
[0044]
The operations of conveying the document and turning the front and back are controlled in relation to the operation of the entire digital color copying machine 1.
[0045]
The image reading unit 110 is disposed below the document table in order to read an image of the document conveyed on the document table 111 by the double-sided automatic document feeder 112. The image reading unit 110 includes document scanning bodies 113 and 114 that reciprocate in parallel along the lower surface of the document table 111, an optical lens 115, and a CCD line sensor 116 that is a photoelectric conversion element.
[0046]
The document scanning bodies 113 and 114 are composed of a first scanning unit 113 and a second scanning unit 114. The first scanning unit 113 has an exposure lamp that exposes the surface of the document image and a first mirror that deflects the reflected light image from the document in a predetermined direction, and is constant with respect to the lower surface of the document table 111. While reciprocally moving in parallel at a predetermined scanning speed. The second scanning unit 114 includes second and third mirrors that deflect the reflected light image from the original deflected by the first mirror of the first scanning unit 113 further in a predetermined direction. The reciprocating unit 113 is reciprocated in parallel while maintaining a constant speed relationship.
[0047]
The optical lens 115 reduces the reflected light image from the original deflected by the third mirror of the second scanning unit 114 and forms the reduced light image at a predetermined position on the CCD line sensor 116. .
[0048]
The CCD line sensor 116 sequentially photoelectrically converts the formed light image and outputs it as an electrical signal. The CCD line sensor 116 is a three-line color CCD capable of reading a black and white image or a color image and outputting line data separated into R (red), G (green), and B (blue) color components. . The R, G, and B document image information (image data) converted into electrical signals by the CCD line sensor 116 is further transferred to the image data processing circuit 10 shown in FIG. 3 for predetermined image data processing. Is done. The image data processing in the image data processing circuit 10 will be described later.
[0049]
Next, the configuration of the image forming unit 210 and the configuration of each unit related to the image forming unit 210 will be described.
[0050]
Below the image forming unit 210, a paper feed mechanism 211 that separates sheets (recording media) P stacked and accommodated in the paper tray 230 one by one and supplies them to the image forming unit 210 is provided. . The sheets P separated and supplied one by one are transported to the image forming unit 210 with timing controlled by a pair of registration rollers 212 arranged in front of the image forming unit 210. Further, the paper P on which an image is formed on one side is re-supplied and conveyed to the image forming unit 210 in synchronization with the image formation of the image forming unit 210.
[0051]
A transfer conveyance belt mechanism 213 is arranged below the image forming unit 210. The transfer / conveying belt mechanism 213 includes a driving roller 214, a driven roller 215, and a transfer / conveying belt 216. The transfer conveyance belt 216 is stretched between the driving roller 214 and the driven roller 215 so as to extend substantially in parallel, and conveys the sheet P by electrostatically adsorbing it.
[0052]
Further, a fixing device 217 is disposed on the downstream side of the transfer conveyance belt mechanism 213 in the sheet conveyance path. The fixing device 217 includes a pair of fixing rollers. When the paper P passes between the rollers, the toner image transferred and formed on the paper P is fixed on the paper P. The paper P that has passed through the fixing device 217 passes through a transport direction switching gate 218 and is discharged from a discharge roller 219 onto a paper discharge tray 220 attached to the outer wall of the digital color copying machine 1.
[0053]
Further, the switching gate 218 selectively selects a conveyance path of the fixed sheet P between a path for discharging the sheet P to the sheet discharge tray 220 and a path for resupplying the sheet P toward the image forming unit 210. Switch to. The paper P whose transport direction has been switched again toward the image forming unit 210 by the switching gate 218 is turned upside down via the switchback transport path 221 and then supplied again to the image forming unit 210.
[0054]
Further, above the transfer conveyance belt 216 in the image forming unit 210, in close proximity to the transfer conveyance belt 216, the first image forming station Pa, the second image forming station Pb, the third image forming station Pc, and A fourth image forming station Pd is arranged in order from the upstream side of the paper transport path.
[0055]
The transfer conveyance belt 216 is frictionally driven by the driving roller 214 in the direction indicated by the arrow Z in FIG. 2, and holds the paper P fed through the paper feed mechanism 211 as described above. The sheet P passes through the image forming stations Pa, Pb, Pc, and Pd in this order.
[0056]
Each of the image forming stations Pa, Pb, Pc, and Pd includes photosensitive drums 222a, 222b, 222c, and 222d that are rotationally driven in the direction of arrow F shown in FIG.
[0057]
In the first image forming station Pa, a charger 223a, a developing device 224a, a transfer discharger 225a, and a cleaning device 226a are sequentially arranged along the rotation direction of the photosensitive drum 222a.
[0058]
A laser beam scanner unit 227a is provided above the photosensitive drum 222a. The laser beam scanner unit 227a exposes the image data processed by the image data processing circuit 10 onto the photosensitive drum 222a. The laser beam scanner unit 227a includes a semiconductor laser element (not shown), a polygon mirror (deflecting device) 240a, an fθ lens 241a, a mirror 242a, a mirror 243a, and the like.
[0059]
The charger 223a uniformly charges the photosensitive drum 222a. The developing device 224a develops the electrostatic latent image formed on the photosensitive drum 222a. The transfer discharger 225a transfers the toner image on the photosensitive drum 222a onto the paper P. The cleaning device 226a removes the toner remaining on the photosensitive drum 222a.
[0060]
A semiconductor laser element (not shown) emits dot light modulated according to image data. The polygon mirror 240a deflects the laser beam from the semiconductor laser element in the main scanning direction. The fθ lens 241a and the mirrors 242a and 243a further reflect and deflect the laser beam deflected by the polygon mirror 240a to form an image on the surface of the photosensitive drum 222a.
[0061]
Each of the image forming stations Pb, Pc, and Pd has substantially the same configuration as that of the first image forming station Pa.
[0062]
Accordingly, at the second image forming station Pb, a charger 223b, a developing device 224b, a transfer discharger 225b, and a cleaning device 226b are sequentially arranged along the rotation direction of the photosensitive drum 222b.
[0063]
A laser beam scanner unit 227b is provided above each photosensitive drum 222b. The laser beam scanner unit 227b includes a semiconductor laser element (not shown), a polygon mirror (deflecting device) 240b, an fθ lens 241b, a mirror 242b, a mirror 243b, and the like.
[0064]
In the third image forming station Pc, a charger 223c, a developing device 224c, a transfer discharger 225c, and a cleaning device 226c are sequentially arranged along the rotation direction of the photosensitive drum 222c.
[0065]
A laser beam scanner unit 227c is provided above each photosensitive drum 222c. The laser beam scanner unit 227c includes a semiconductor laser element (not shown), a polygon mirror (deflecting device) 240c, an fθ lens 241c, a mirror 242c, a mirror 243c, and the like.
[0066]
In the fourth image forming station Pd, a charger 223d, a developing device 224d, a transfer discharger 225d, and a cleaning device 226d are sequentially arranged along the rotation direction of the photosensitive drum 222d.
[0067]
A laser beam scanner unit 227d is provided above each photosensitive drum 222d. The laser beam scanner unit 227d includes a semiconductor laser element (not shown), a polygon mirror (deflecting device) 240d, an fθ lens 241d, a mirror 242d, a mirror 243d, and the like.
[0068]
The laser beam scanner unit 227a has image data corresponding to the black component image of the color document image, and the laser beam scanner unit 227b has image data corresponding to the cyan component image of the color document image. Is inputted with image data corresponding to the magenta color component image of the color original image, and the laser beam scanner unit 227d is inputted with image data corresponding to the yellow color component image of the color original image.
[0069]
As a result, electrostatic latent images corresponding to the color-converted image data are formed on the photosensitive drums 222a, 222b, 222c, and 222d. The developing device 224a contains black toner, the developing device 224b contains cyan toner, the developing device 224c contains magenta toner, and the developing device 224d contains yellow toner. The electrostatic latent images on the photosensitive drums 222a, 222b, 222c, and 222d are developed with toners of these colors. As a result, the image data color-converted by the image data processing circuit 10 is reproduced as a toner image of each color.
[0070]
Further, a sheet suction charger 228 is provided between the first image forming station Pa and the sheet feeding mechanism 211. The sheet adsorbing charger 228 charges the surface of the transfer / conveying belt 216, and the sheet P supplied from the paper feeding mechanism 211 is securely adsorbed onto the transfer / conveying belt 216 in the first image forming station Pa. To the fourth image forming station Pd.
[0071]
On the other hand, a static eliminator 229 is provided almost directly above the drive roller 214 between the fourth image station Pd and the fixing device 217. An AC current for separating the sheet P electrostatically attracted to the transport belt 216 from the transfer transport belt 216 is applied to the static eliminator 229.
[0072]
In the digital color copying machine 1 configured as described above, cut sheet-like paper is used as the paper P. The paper P is sent out from the paper tray 230 and supplied into the guide of the paper feed conveyance path of the paper feed mechanism 211. The leading end portion of the paper P is detected by a sensor (not shown), and is temporarily stopped by the pair of registration rollers 212 based on a detection signal output from the sensor.
[0073]
The sheet P is fed onto the transfer conveyance belt 216 rotating in the direction of the arrow Z in FIG. 2 in time with the image forming stations Pa, Pb, Pc, and Pd.
[0074]
In each of the image forming stations Pa, Pb, Pc, and Pd, toner images of respective colors are formed, transferred onto the paper P that is electrostatically attracted by the transfer and transport belt 216, and superimposed. When the transfer of the image by the fourth image forming station Pd is completed, the sheet P is sequentially peeled off from the transfer conveyance belt 216 by the discharger 229 from the leading end portion and guided to the fixing device 217. The paper P on which the toner image is fixed is discharged from a paper discharge port (not shown) to the paper discharge tray 220.
[0075]
Note that the above description relates to a configuration in which laser beam scanner units 227a, 227b, 227c, and 227d perform optical writing on a photosensitive member by scanning and exposing a laser beam. However, instead of the laser beam scanner unit, a writing optical system (LED head) including a light emitting diode array and an imaging lens array may be used. The LED head is smaller than the laser beam scanner unit and has no moving parts and is silent. Therefore, it can be suitably used in an image forming apparatus such as a tandem digital color copying machine 1 that requires a plurality of optical writing units.
[0076]
Next, image data processing in the image data processing circuit 10 will be described. The tracking pattern image is subjected to additional processing in the image data processing circuit 10.
[0077]
By the way, the tracking pattern image is formed by forming a plurality of pixels in a matrix of (several pixels) × (several pixels) to (several tens of pixels) × (several tens of pixels) in a copy at a density different from that of the original. It is formed by giving a specific meaning to the arrangement of pixels. By reading the arrangement of the pixels with a reading device, information such as when and with which device the copy was copied can be obtained. Note that the tracking pattern image is preferably added at a small interval so that the tracking pattern image is included even if the image to be formed is small, such as a stamp.
[0078]
FIG. 3 shows an image data processing circuit 10 in the present embodiment. The image data processing circuit 10 performs image data processing on each of the R, G, and B image data sent from the image data input means 11 such as the CCD line sensor 116 of FIG. 2, and laser beam scanner units 227a and 227b.・ Send to 227c ・ 227d The image data processing circuit 10 includes a color conversion unit 12 and image processing units 13, 14, 15, and 16. Further, the tracking pattern image is added to color image data (yellow image data) corresponding to the yellow component color that is the most difficult to visually recognize among the component colors used for image formation so as not to be visually noticeable. Is preferred. Therefore, the image data processing circuit 10 for yellow image data further includes a density conversion unit 17, a selection unit 18, and a memory 19 for adding a tracking pattern image.
[0079]
The color conversion unit 12 converts RGB data, which is color image data sent from the image data input unit 11, into YMCK data, which is color image data necessary for image formation in the image forming unit 210. Here, RGB data is color image data corresponding to the three primary colors (R, G, B) of light, and YMCK data is color image data corresponding to four colors of yellow, magenta, cyan, and black. is there.
[0080]
The image processing units 13, 14, 15, and 16 provided corresponding to yellow, magenta, cyan, and black color signals perform processing such as region separation processing, color correction processing, zoom processing, and halftone processing. Here, the area separation process is a process for determining and separating for each area whether the input data corresponds to a character portion, a halftone dot photograph, or a photographic paper photograph. The color correction process is to adjust each color of the color image data based on the color conversion table. The zoom process is a magnification conversion of input image data based on a set magnification. The halftone process is a process for expressing gradation such as multilevel error diffusion and multilevel dither. In the present embodiment, the image processing circuit 10 including four color image data of yellow, magenta, cyan, and black is described. However, the present invention is not limited to this, and for example, yellow, magenta, You may use the image processing circuit comprised from the color image data of three colors of cyan.
[0081]
The yellow image data output from the image processing unit 13 is input to the density conversion unit 17. The yellow image data input to the density conversion unit 17 is density-converted based on a method described later. Some yellow image data are output directly from the image processing unit 13 without going through the density conversion unit 17, and some are output through the density conversion unit 17. Both of the two output data are input to the selector 18. In the selection unit 18, based on data (tracking information data) for forming a tracking pattern image stored in the memory 19, for each pixel corresponding to each input image data, which one of the two output data is selected. Select either one. Then, the selection unit 18 outputs only the selected output data. That is, the selection unit 18 selects and outputs the output data from the density conversion unit 17 as the image data corresponding to the pixels to form the tracking pattern image, and the image data corresponding to the other pixels includes the image data. Output data from the processing unit 13 is selected and output.
[0082]
In the present embodiment, the density conversion unit 17 performs density conversion on all image data, and the selection unit 18 selects image data whose density has been converted only for pixels that should form the tracking pattern image. . However, the present invention is not limited to this, and the density conversion unit 17 may perform density conversion only on image data corresponding to pixels that should form the tracking pattern image.
[0083]
As shown in FIG. 4, the yellow image data output from the selection unit 18 is obtained by converting the density of only the pixels constituting the tracking pattern image. In FIG. 4, the height of the portion not hatched indicates the density of the image data before density conversion. In FIG. 4, the hatched portion on one side indicates the density amount obtained by density conversion of the pixels constituting the tracking pattern image in the low density area and the middle density area. The shaded portions on both sides indicate the density after density conversion by subtraction is performed on the pixels constituting the tracking pattern image in the high density area. Each density A ′, A, B ′, 255 of the yellow image data in FIG. 4 and the density amount C2 to be subtracted are as described with reference to FIG.
[0084]
Further, the image data output from the selection unit 18 is input to the laser beam scanner unit 227d. For image data other than yellow, that is, magenta, cyan, and black, the image data output from the image processing units 14, 15, and 16 is input to the laser beam scanner units 227c, 227b, and 227a. Is done.
[0085]
In the present embodiment, the image reading unit 110 provided in the digital color copying machine 1 is used as the image data input unit 11. However, the image data input means in the present invention is not limited to this, and other document reading devices, scanners, personal computers, and other devices connected to the color copying machine can also be used. The digital color copying machine 1 may be provided with a cable or an interface with communication means using light or radio waves. Thereby, a tracking pattern image can be added also to image data input from the outside.
[0086]
Next, a tracking pattern image addition process performed on yellow image data will be described. FIG. 1 is a flowchart showing a flow of the tracking pattern image adding process in the image data processing circuit (image processing apparatus) 10 shown in FIG. Note that the flowchart of FIG. 1 shows only processing related to yellow image data.
[0087]
When image data is input (S1), first, the color conversion process described above is performed in the color conversion unit 12 (S2). Subsequently, the image processing unit 13 performs image processing such as the region separation processing described above (S3). Then, the density conversion unit 17 adds the tracking pattern image by the following method.
[0088]
First, the density conversion unit 17 determines whether the density indicated by the yellow image data sent from the image processing unit 13 corresponds to a low density range, a middle density range, or a high density range (S4 and S5). That is, as a first step, the density conversion unit 17 determines whether or not the density of the yellow image data is α or less (S4). Here, the density α is a density at the boundary between the low density area and the middle density area. When the density is equal to or less than α (YES in S4), the yellow image data is determined to be image data belonging to the low density area. The If the density is higher than α (NO in S4), as a second step, the density conversion unit 17 determines whether the density of the yellow image data is equal to or lower than β ′. Here, the density β ′ is a density at the boundary between the medium density area and the high density area. When the density is equal to or less than β ′ (YES in S5), the yellow image data is determined to be image data belonging to the medium density area. The When the density is higher than β ′ (NO in S5), the yellow image data is determined as image data belonging to the high density region.
[0089]
Subsequently, the yellow color image data divided into the density areas is subjected to a tracking pattern image addition process by the density conversion unit 17 in a different manner for each area. That is, the image data belonging to the low density area is subjected to the tracking pattern image addition process (that is, density conversion process) in the low density area (S6). The image data belonging to the middle density area is subjected to a tracking pattern image addition process (density conversion process) in the middle density area (S7). The image data belonging to the high density area is subjected to a tracking pattern image addition process (density conversion process) in the high density area (S8).
[0090]
The yellow image data that has been subjected to different tracking pattern addition processing for each density region is sent to the selection unit 18. Then, for the pixels constituting the tracking pattern image based on the tracking information data stored in the memory 19, the density-converted data is adopted (S9), and the processing is ended (END). Although not shown, image data from the image processing unit 13 is selected by the selection unit 18 as described above for pixels that do not constitute the tracking pattern image.
[0091]
Next, an example of density conversion processing performed in each of the density areas will be described with reference to FIG. FIG. 5 shows yellow image data (input data) immediately before density conversion processing (hereinafter simply referred to as “density conversion processing”) in the density conversion unit 17 and a yellow image immediately after density conversion is performed. It is a graph which shows the relationship with data (output data). In FIG. 5, the density of the output data with respect to the density of the input data when the density conversion process is not performed is indicated by a one-dot chain line. In this case, the input data density is equal to the output data density.
[0092]
In FIG. 5, the density range of the input data is a low density area from 0 to α, a middle density area from α to β or β ′, and a high density area from β or β ′ to the highest density. In the present embodiment, the boundary α between the low concentration region and the intermediate concentration region is included in the low concentration region, and the boundary β or β ′ between the intermediate concentration region and the high concentration region is included in the intermediate concentration region. However, the boundary between the low concentration region and the intermediate concentration region may be included in the low concentration region or the intermediate concentration region, and the boundary between the intermediate concentration region and the high concentration region may be included in the intermediate concentration region or the high concentration region. In the present embodiment, for example, when the maximum density is 255, α is set to any value in the range of 40 to 60. Β or β ′ is set to any value in the range of 150 to 170. Β and β ′ will be described later.
[0093]
First, the density conversion process in the low density range will be described below. In the low density region, it is preferable that the tracking pattern image is added by a method of adding density to the input data. Further, the density of the output data after density conversion may be constant at the value A indicated by the broken line in FIG. 5 in the low density region. Further, as indicated by a solid line in FIG. 5, the density addition amount (density conversion amount) is gradually reduced so that the density of the output data becomes a density from A ′ to A as the density of the input data increases. May be. Alternatively, the density of the output data may be converted within the hatched range in FIG.
[0094]
Here, A is about 100 in this embodiment, and A ′ is 70. Note that A ′ is preferably set to be equal to or higher than the lowest density that can be read by the tracking pattern image reading device (reading device) so that the tracking pattern image can be surely recognized in the entire density region. This minimum density varies depending on the characteristics of the image forming unit 210 (see FIG. 2).
[0095]
If the density of the tracking pattern image is too low, the tracking pattern image cannot be stably formed. If the density becomes high to some extent, a stable tracking pattern image can be formed. Therefore, in order to be able to be read by the reading device, it is also necessary that the tracking pattern image can be stably formed.
[0096]
Further, it is more preferable to add the tracking pattern image by decreasing the density addition amount (density conversion amount) as the density of the input data increases so that the density of the output data does not exceed the predetermined density (A). This makes it possible to achieve both the formation of a tracking pattern image that can be reliably recognized by the reading device and the formation of a tracking pattern image that is visually inconspicuous. In this case, A is preferably set within a density range that is not visually noticeable when the tracking pattern image is added.
[0097]
Next, density conversion processing in the middle density range will be described below. In the middle density region, it is preferable to add the tracking pattern image by a method of adding density to the input data. Therefore, the density addition amount for obtaining the tracking pattern image is a constant value as shown by a two-dot chain line in FIG. 5 or increases according to the density of the input data as shown by a solid line in FIG. However, the latter is more preferable because it is less noticeable. Further, the density of the output data may be converted within a range between the solid line and the two-dot chain line. The specific value may be set according to the characteristics of the image forming unit 210 or the like so that it is difficult to visually recognize and when the tracking pattern image is read reliably. When α is 40 and A is 100, the constant value is 60.
[0098]
In the present embodiment, the intermediate concentration range is a range from α to β or β ′. Here, β is the value of the input data when the density of the output data becomes the maximum density 255. For example, when adding a density of a constant value 100 over the entire middle density range, the output data becomes 255 when β is 155. That is, the density B of the output data when the density conversion process is not performed on the input data is 155, and the output data after the density conversion process of adding 100 to this is 255. This β value may be used as the boundary between the medium concentration range and the high concentration range.
[0099]
However, in the image forming apparatus according to the present invention, γ correction may be performed in the image forming unit 210 according to the display density characteristics of each image forming unit 210 after the density conversion process. Considering that the density of the image data corrected by the γ correction is likely to change to the high density side, β ′ smaller than β is preferably set as the boundary. That is, γ correction is determined based on the characteristics of the image forming unit 210, and generally γ ≠ 1. When the output data from the density conversion unit 17 is set to the maximum density, it becomes necessary to convert the output data to a value exceeding the maximum density by γ correction of γ ≠ 1, but actually such conversion is performed. The inconvenience that it is not possible occurs. Considering this, it is preferable to set the boundary to β ′.
[0100]
Subsequently, the density conversion process in the high density area will be described below. In the high density region, it is preferable that the tracking pattern image is added by a method of subtracting the density from the input data. When the constant density C2 is subtracted from the density of the input data, the density of the output data as shown by the solid line in FIG. 5 is obtained. Further, when the density A ′ is constant regardless of the density of the input data, the density of the output data as shown by the broken line in FIG. 5 is obtained. In the high density range, any of the above methods may be used, and density conversion may be performed within a hatched range between the solid line and the broken line. In the high density region, it is necessary to ensure that the tracking pattern image can be read in the same manner as in the low density region. However, the density after density conversion is preferably A ′ or more in order to make it less noticeable. In addition, if the difference between the density of the input data and the density after density conversion becomes larger than necessary, the tracking pattern image becomes more noticeable than necessary, and the density conversion processing is preferably performed within a range close to the solid line. It is preferable that the density subtraction amount (density conversion amount) be constant so that the density after density conversion becomes a solid line value.
[0101]
In this embodiment, for example, β ′ is 150, and the density addition amount C1 in the density conversion process at the density β ′ of the input data is 85. In this case, since A ′ is 70 and B ′ is 150, the density difference C2 between A ′ and B ′ is 80, and C1 and C2 are substantially equal.
[0102]
The specific values described above are not limited to this, and may be arbitrarily set depending on characteristics of the image forming unit 210 that outputs image data to which a tracking pattern image is added.
[0103]
In this embodiment, the density conversion is performed by adding to the density of the original image data or by subtracting from the density of the original image data. However, the present invention is not limited to this, and the density conversion is performed by converting the density of the original image data to a higher density side than that density, or by converting the density of the original image data to a lower density side than that density. May be performed. Therefore, in addition to the method of adding and subtracting by calculation, for example, density conversion may be performed using a table in which the density before conversion is associated with the density after conversion.
[0104]
In the present embodiment, the density area to which the image data of each pixel belongs is divided into three different density areas, a low density area, a medium density area, and a high density area. However, in the present invention, each density area is further divided. May be divided into two or more density regions, and a tracking pattern image may be added by a different method for each of the divided density regions.
[0105]
For example, as shown in FIG. 6, the above-described middle density region may be further divided into two different density regions in the density value β ″. In this case, there are four different density regions. Among the two density ranges, the density value ranges from 0 to α, the low density range, the density value ranges from α to β ", the middle density range (1), and the density value ranges from β" to β or β '. The density range {circle over (2)} and the density value from β or β ′ to 255 are set as the high density range, where the middle density range {circle over (1)} and the middle density range {circle around (2)} belong to the middle density range. In addition, it is sufficient that the density indicated by the image data belongs to at least one of the low density area, the medium density area, and the high density area.
[0106]
As shown by a two-dot chain line in FIG. 6, in the middle density region (1), the density addition amount for making a tracking pattern image is preferably a constant value, and in the middle density region (2), It is preferable to increase the density addition amount according to the density of the input data. In the low density region and the high density region, the tracking pattern image may be added in the same manner as in the above embodiment.
[0107]
According to this method, it is possible to add a more desirable tracking pattern image according to the density of each image data.
[0108]
【The invention's effect】
As described above, in the image processing method of the present invention, the step of determining whether the density indicated by the image data to which the tracking pattern image is to be added belongs to at least a low density area, a middle density area, or a high density area. If the density indicated by the image data belongs to a low density area or a medium density area, the density of the image data is converted to a density higher than the density by a method different for each density area, and the image data And the step of converting the density of the image data to a lower density side than that density.
[0109]
According to the above method, by dividing the image data of the document into the above three types of areas according to the density, it is possible to add the tracking pattern image by a method suitable for each density area. Thereby, the tracking pattern image can be satisfactorily read in the entire density range, and the tracking pattern image can be made inconspicuous.
[0110]
Specifically, in the low density region and the middle density region, the density of the image data is increased by converting the density to a higher density side than the density of the image data. Here, density conversion is performed by a method different from that for the middle density area, taking into consideration difficulty in reading the tracking pattern image and conspicuousness especially in the low density area. As a result, the tracking pattern image can be satisfactorily read even in the low density region, and the tracking pattern image can be made inconspicuous.
[0111]
In the high density range, the density of the image data is lowered by converting the density to a lower density side than the density of the image data. As a result, the image data after density conversion, which may occur when the density of the image data is converted to the high density side in the high density area, exceeds the maximum density in the image data, and the pixel to which the tracking pattern image is added And the problem that it becomes impossible to distinguish from other pixels not added.
[0112]
Therefore, according to the method described above, tracking is possible for the reading apparatus to perform good reading with low visibility to the human eye, regardless of the range of the image data density of the document. An image processing method for adding a pattern image can be provided.
[0113]
Further, the image processing apparatus of the present invention determines whether the density indicated by the image data to which the tracking pattern image is to be added belongs to at least a low density area, a middle density area, or a high density area, and the image When the density indicated by the data belongs to the low density area or the middle density area, the density of the image data is converted to a density higher than the density by a method different for each density area, and the density indicated by the image data is In the case of belonging to a high density region, a density conversion unit for converting the density of the image data to a density lower than the density is provided.
[0114]
According to the above configuration, as with the image processing method described above, the human eye has low visibility regardless of the range of the density of the image data of the document, and good reading for the reading device. It is possible to provide an image processing apparatus that adds a tracking pattern image that can be performed.
[0115]
In the image processing method described above, it is preferable that the tracking pattern image is added to yellow color image data among yellow (Y), magenta (M), and cyan (C) color image data.
[0116]
According to the above method, yellow has the lowest visibility among the above three colors. Therefore, if yellow color image data is used for adding tracking information, the influence on the image quality of the copy is minimized. be able to.
[0117]
Also in the above-described image processing apparatus, it is preferable that the density conversion unit performs density conversion on yellow color image data. Thereby, the same effect as the image processing method described above can be obtained.
[0118]
In the image processing method described above, when the density indicated by the image data belongs to a low density range, the density conversion is performed so that the density after density conversion is equal to or higher than the lowest density that can be recognized by a reading device that reads the tracking pattern image. It is preferable.
[0119]
According to the above method, the added tracking pattern image can be read for all image data in the low density region. That is, in the low density area, if the density of the original image data is low, there may occur a case where the reading apparatus cannot recognize the tracking pattern image by adding the density. However, if the tracking pattern image is added by the above method, all the tracking pattern images can be reliably read.
[0120]
In the image processing apparatus, the density conversion unit may be configured such that when the density indicated by the image data belongs to a low density range, the density after density conversion is the lowest density that can be recognized by a reading device that reads the tracking pattern image. It is preferable to perform density conversion so as to achieve the above. Thereby, the same effect as the image processing method described above can be obtained.
[0121]
In the image processing method described above, when the density indicated by the image data belongs to a low density range, it is more preferable to perform density conversion so that the density conversion amount decreases as the density of the image data before density conversion increases.
[0122]
The tracking pattern image can be easily read by increasing the density conversion amount with respect to the density of the original image data. However, if the tracking pattern image is added with a density conversion amount that is too large relative to the density of the original image data, the tracking pattern image becomes visually conspicuous, and the image quality of a copy or the like deteriorates. Invite. Therefore, according to the above method, the density conversion amount becomes smaller as the density of the image data becomes higher in the low density region, so that the tracking pattern image can be prevented from becoming visually noticeable. Therefore, it is possible to achieve both the formation of a reliable tracking pattern image that can be easily recognized by the reading device and the formation of a tracking pattern image that is visually inconspicuous.
[0123]
In the image processing apparatus, when the density indicated by the image data belongs to a low density region, the density conversion unit decreases the density conversion amount as the density of the image data before density conversion increases. It is more preferable to convert the density. Thereby, the same effect as the image processing method described above can be obtained.
[0124]
In the above image processing method, when the density indicated by the image data belongs to a high density range, it is preferable that the density after density conversion is converted to a density higher than the lowest density that can be recognized by a reading device that reads the tracking pattern image. .
[0125]
According to the above method, the image data in the high density region can be subtracted to the density within the range recognizable by the reading device. Thereby, a tracking pattern image can be recognized reliably.
[0126]
In the image processing apparatus, the density conversion unit may be configured such that when the density indicated by the image data belongs to a high density range, the density after density conversion is the lowest density that can be recognized by a reading device that reads the tracking pattern image. It is preferable to convert the density as described above. Thereby, the same effect as the image processing method described above can be obtained.
[0127]
In the above image processing method, when the density indicated by the image data belongs to a high density range, it is more preferable to perform density conversion so that the density conversion amount is constant.
[0128]
If the difference between the density of the original image data and the density after the density conversion process becomes larger than necessary, there arises a problem that the tracking pattern image becomes visually noticeable. According to the above method, it is possible to prevent a difference in density before and after density conversion from increasing, and to prevent the tracking pattern image from becoming visually noticeable in a high density region. Therefore, it is possible to achieve both the formation of a reliable tracking pattern image that can be easily recognized by the reading device and the formation of a tracking pattern image that is visually inconspicuous.
[0129]
In the image processing apparatus, it is more preferable that the density conversion unit performs density conversion so that the density conversion amount is constant when the density indicated by the image data belongs to a high density range. Thereby, the same effect as the image processing method described above can be obtained.
[0130]
In the image processing method described above, when the density indicated by the image data belongs to the middle density range, it is preferable to perform density conversion so that the density after density conversion is less than the highest density in the image data.
[0131]
According to the above method, after the tracking pattern image is added, all image data belonging to the middle density region is converted to a density less than the highest density in the image data. Therefore, it is possible to reliably add the density amount to be added, and the tracking pattern image can be easily recognized.
[0132]
Further, in the image processing apparatus, the density conversion unit is configured so that when the density indicated by the image data belongs to a middle density range, the density after density conversion is less than the maximum density in the image data. It is more preferable to convert. Thereby, the same effect as the image processing method described above can be obtained.
[0133]
An image forming apparatus according to the present invention includes the above-described image processing apparatus and an image forming unit that forms an image based on image data whose density has been converted by the image processing apparatus.
[0134]
According to the above configuration, since the image forming apparatus includes the above-described image processing apparatus, the human eye has low visibility regardless of the density of the image data of the document. An image to which a tracking pattern image that can be read satisfactorily can be added to the reading device. Therefore, it is possible to easily and reliably recognize tracking information for all copies and the like, which is useful for preventing counterfeiting of banknotes and securities. In addition, other copies can be copied without adversely affecting image quality.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a flow of a tracking pattern image addition process performed by an image data processing circuit in an embodiment of the present invention.
FIG. 2 is a front cross-sectional view showing the configuration of a digital color copying machine as an embodiment of the image forming apparatus according to the present invention.
FIG. 3 is a block diagram showing an image data processing circuit in an embodiment of the present invention.
4 is a graph showing an output example of yellow image data from the selection unit shown in FIG. 3; FIG.
FIG. 5 is a graph showing an example of tracking pattern image addition performed in the density conversion unit shown in FIG. 3 and showing the relationship between input data before density conversion and output data after conversion.
6 is a graph showing another example of tracking pattern image addition performed in the density conversion unit shown in FIG. 3 and showing the relationship between input data before density conversion and output data after conversion. .
[Explanation of symbols]
1 Digital color copier (image forming device)
12 color converter
13 Image processing unit (image processing device)
17 Density converter
18 Selector
19 Memory
210 Image forming unit
Pd laser beam scanner unit

Claims (13)

In an image processing method for performing density conversion on image data representing an image of a document in order to add a tracking pattern image to the image of the document,
Determining whether the density indicated by the image data of the pixels constituting the tracking pattern image belongs to at least one of a low density area, a medium density area, and a high density area;
When the density indicated by the image data belongs to the low density area or the middle density area, the density of the image data is converted to a density higher than the density by a method different for each density area, and the image data indicates concentration if it belongs to the high density range is seen including a step of concentration converting the density of the image data to the low-density side than its concentration,
When the density indicated by the image data belongs to an intermediate density range, the density conversion is performed so that the density after density conversion is less than the highest density in the image data. Image data indicating an image of a document is configured to include yellow, magenta, and cyan color image data.
2. The image processing method according to claim 1, wherein the addition of the tracking pattern image is performed on yellow color image data.   The density conversion is performed such that when the density indicated by the image data belongs to a low density range, the density after density conversion is equal to or higher than a minimum density that can be recognized by a reading device that reads a tracking pattern image. 3. The image processing method according to 1 or 2.   4. The image according to claim 3, wherein when the density indicated by the image data belongs to a low density range, density conversion is performed such that the density conversion amount decreases as the density of the image data before density conversion increases. Processing method.   5. If the density indicated by the image data belongs to a high density range, the density after density conversion is converted to a density higher than a minimum density that can be recognized by a reading device that reads a tracking pattern image. The image processing method according to any one of the above.   6. The image processing method according to claim 5, wherein when the density indicated by the image data belongs to a high density range, density conversion is performed so that the density conversion amount is constant. In an image processing apparatus that performs density conversion on image data indicating an image of a document in order to add a tracking pattern image to the image of the document,
While determining whether the density indicated by the image data of the pixels constituting the tracking pattern image belongs to at least a low density area, a medium density area, or a high density area,
When the density indicated by the image data belongs to the low density area or the middle density area, the density of the image data is converted to a density higher than the density by a method different for each density area, and the image data indicates In the case where the density belongs to a high density region, a density conversion unit that converts the density of the image data to a density lower than the density is provided .
The density conversion unit converts the density so that the density after density conversion is less than the highest density in the image data when the density indicated by the image data belongs to a middle density range. apparatus. Image data indicating an image of a document is configured to include yellow, magenta, and cyan color image data.
The image processing apparatus according to claim 7 , wherein the density conversion unit performs density conversion on yellow color image data. When the density indicated by the image data belongs to a low density range, the density conversion unit converts the density so that the density after density conversion is equal to or higher than a minimum density that can be recognized by a reading device that reads a tracking pattern image. the image processing apparatus according to claim 7 or 8, wherein. When the density indicated by the image data belongs to a low density range, the density conversion unit performs density conversion so that the density conversion amount decreases as the density of the image data before density conversion increases. The image processing apparatus according to claim 9 . The density conversion unit converts the density after density conversion to a density higher than a minimum density that can be recognized by a reading device that reads a tracking pattern image when the density indicated by the image data belongs to a high density range. The image processing apparatus according to any one of claims 7 to 10 . The image processing apparatus according to claim 11 , wherein when the density indicated by the image data belongs to a high density region, the density conversion unit performs density conversion so that a density conversion amount is constant. The image processing apparatus according to any one of claims 7 to 12 ,
An image forming apparatus comprising: an image forming unit that forms an image based on image data whose density has been converted by the image processing apparatus.

Images