JP2006039478A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of added information appearing as noise in an image and deteriorating the quality of an output image because density cannot be adjusted so that it is not conspicuous when the information is added. <P>SOLUTION: In the image forming apparatus, a common region exists for a coloring region producing only by magnetic toner and a coloring region producing only by non-magnetic toner. A switching mechanism is provided for one part of the regions in a color conversion table based on coordinate information and added information. A combination of a minute area forming an image by drawing with only the non-magnetic toner and a minute area forming an image by drawing with the magnetic substance toner is used in the color range for the common range of the color ranges as an imbedding means for added information. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus having a function of adding an information pattern that is difficult to visually discern to a printed output image in an electrophotographic image processing system including a printing mechanism such as a printer or a copying machine. .

  Conventionally, full-color printers, full-color copying machines, full-color facsimile machines, and the like have been put to practical use as output devices for performing color printing.

  As printing output devices such as color copiers and color printers become cheaper and the quality of the output image improves, originals that are prohibited from being copied using them, such as securities and banknotes (hereinafter referred to as “specific originals”) ) Is causing fears of an increase in easy counterfeiting.

  In addition to printed materials with direct value, such as specific manuscripts, copyright protection is also required to protect the rights of image information producers.

  In order to prevent such illegal copying, several measures have been taken in color printing apparatuses.

One of them is a measure for preventing illegal copying by registering an image pattern of a specific document in a color copying machine or a color printer and identifying the specific document by image recognition. (Patent Document 1)
In addition to security purposes such as prevention of unauthorized copying, there are also attempts to embed various additional information in order to improve convenience and provide services using the embedded information.

  For this reason, as a method for specifying a device used for print output, identifying a person who has performed such illegal print output, or adding various information, right information, etc. for convenience However, there has been a search for a method of performing processing for adding various kinds of information to a print output in a visually inconspicuous form.

  For example, among the output color components of color printing (for example, YMCK), the image signal of the color (for example, Y) component that is most difficult for human eyes to identify is subjected to modulation to add a constant value, and This is a technique for adding a pattern representing a production number.

  However, in the above conventional example, since the extra color signal is simply superimposed on the output image, there is a problem that the added signal acts as noise on the original image and the image quality of the output image is lowered. .

  Even if information is added in a color that is most difficult to be identified by the human eye, such a problem particularly occurs in an apparatus in which image formation is performed by binary processing, that is, pseudo halftone processing such as dithering or error diffusion. In this case, there is a drawback that image deterioration is easily noticeable.

  In particular, color printing has a problem in that the overall color is slightly different.

  Further, in the conventional apparatus, when adding extra information, the density cannot be adjusted so that it is not conspicuous. Therefore, the additional information appears as noise in the image, which causes the quality of the output image to be impaired. It has become.

  This is not preferable because the additional information can be seen with the naked eye on the printout.

  In addition to this, there is a method of embedding information in the frequency region of the image. However, in a printed image, it becomes fixed noise and is easily visible in a uniform density region where there is no change in gradation, which is not preferable in terms of print quality.

  In general, in a color printer, in order to make the color development more vivid and improve the image quality, an additional color exceeding the minimum required printing color is prepared and printed out.

  To express black, instead of expressing with a mixed color of cyan, magenta, and yellow, replace with black toner, or prepare light color toner to reduce graininess at light density, and print quality We are trying to improve.

  In a printer having these additional colors, it is possible to embed information by changing the combination of toners when expressing the same color.

For example, when expressing the same cyan color, use a lot of light cyan toner, use a little dark cyan toner, or how much black is replaced by cyan, magenta, yellow, etc. The amount changes.
Japanese Patent Laid-Open No. 04-294682

  However, in actual print output of a specific color expression, there is no easy method for determining whether the color of a minute area is a composite color of cyan, magenta and yellow or a single black color.

  The fact that it can be optically determined by reading with a scanner means that it is easy to visually recognize even in human vision, which is not desirable.

  This is because the color expression is often different in practice, which is undesirable because it results in human recognition of information embedding.

  Further, when additional magnetic toner is prepared and additional information is embedded in the image, an extra mechanism for the magnetic toner is required as a mechanism, or performance is deteriorated.

  When an optical mechanism and a developing mechanism for magnetic toner are added to the mechanism that prints out four colors in succession, the size of the printing mechanism becomes larger, the path of the shared paper transport mechanism becomes longer, and the main part of the cost of the mechanism The optical mechanism and the developing mechanism that occupy a large area will be increased.

  In the mechanism of the method of layering colors one by one, the cost of the mechanism itself does not increase, but this time the performance will surely decrease by 20%.

  Also, an extra page memory is required for the image processing mechanism.

  In addition, it is difficult to find a colorless material that meets the requirements of cost and coercive force as a magnetic material. Magnetic toner often becomes colored toner, and it is necessary to consider interference with the original image.

  The present invention has been made in view of the drawbacks of the above-described conventional examples, and the object of the present invention is that it is difficult to visually recognize without adding a special mechanism or reducing performance, It is to provide an additional information embedding method that is easy to detect.

  In order to solve the above problems, the present invention employs a configuration in which magnetic toner and non-magnetic toner are used in combination as the configuration of the printing mechanism.

  In electrophotographic printing mechanisms such as laser printers and LED printers, the magnetic force, attractive force between charges, repulsive force, etc. are used to supply the toner, develop the latent image, and transfer the toner image. Creating toner.

  There are several types of developing mechanism configurations. For example, a two-component developing mechanism that uses a mixture of two components called toner and carrier, and a single-component toner that does not have a carrier component. The pigments of the one-component developing mechanism are compared.

  In the toner containing the pigment for printing and the two-component toner obtained by separating the magnetic carrier, the toner on the printed paper has almost no magnetic material and can be regarded as almost non-magnetic toner.

  On the other hand, in the one-component toner in which the toner and the carrier are integrated, which is itself a magnetic material and also a pigment, the toner on the printed paper is a magnetic material and can be regarded as a magnetic toner.

  The development mechanism for single-component toner and two-component toner has many factors that can be shared, and there is almost no increase in the cost of the mechanism.

  As a toner color distribution, a combination capable of reproducing the same color gamut in the magnetic toner group and the non-magnetic toner group is adopted.

  As the simplest example, magnetic toner is assigned to black, and nonmagnetic toner is assigned to three colors of cyan, magenta, and yellow.

  By allocating such information, embedding of additional information can be performed by switching the selection of printing expression in black alone and mixed color expression of cyan, magenta, and black by controlling coordinates and embedding information for the same color in the gray region. It becomes possible to do.

  By using the magnetic toner and the non-magnetic toner together, it is not necessary to prepare an extra optical mechanism, a developing mechanism, and a toner replenishing mechanism for one color, and it is possible to embed magnetic information without causing a decrease in performance.

  The specific additional information embedding means includes a plurality of color conversion tables for all or a part of the color conversion table, and at least a part including a color gamut that can reproduce the same color by a set of magnetic toner and a set of non-magnetic toner. Then, the table is selected based on the coordinate information and the modulation information of the additional information, and the information is embedded.

  By switching the color conversion table, the input color is converted into a different combination of toner groups, and the magnetic characteristics of the print target region are recorded while fluctuating.

  By scanning the print output image with the magnetic sensor, it is possible to detect and output additional information.

  As described above, by using the color conversion table in which the color gamut colors that can be expressed only by the magnetic toner set and only the non-magnetic toner set can be switched by the modulation information of the additional information, the print output image can be added Without additional optical drawing system, latent image development system, and pigment replenishment system, it is possible to embed additional information magnetically without causing performance degradation, and more easily read out additional information It becomes possible to provide a system.

(First embodiment)
FIG. 1 shows a main part of an image processing block and a main block diagram of a printing mechanism as the structure of the main mechanism of the first embodiment of the present invention.

  201 is a means for inputting image information and drawing information from an external device.

  Reference numeral 202 denotes a scanner.

  A control unit 203 controls the image processing mechanism.

  Reference numeral 204 denotes a storage unit that stores a table and a driving procedure of the control unit.

  A work area memory 205 is used for temporary storage of data, storage of variables, development of font images, and the like.

  A conversion table 220 replaces input color information with CMYK colors that are print colors.

  A drawing processor 206 expands an image bitmap on the page memory.

  Reference numerals 207 to 210 denote page memories for developing respective color images of cyan, magenta, yellow, and black.

  Reference numerals 211 to 214 denote drive circuits for controlling the optical circuit of the printing mechanism.

  The printing mechanism is a four-color printing mechanism, and black (abbreviated as K) toner uses magnetic toner, and cyan, magenta, and yellow (abbreviated as C, M, and Y respectively) use non-magnetic toner. .

  Reference numerals 101 to 104 denote optical driving and scanning circuits which perform light drawing on the photosensitive member to form a potential latent image.

  Reference numerals 105 to 108 denote toner replenishment systems, and reference numeral 105 denotes a magnetic toner. 106 to 108 supply non-magnetic toner.

  Reference numerals 109 to 112 denote photosensitive members, which develop a latent image generated by an optical drawing system with toner, and transfer the toner image to a transfer member.

  Reference numeral 120 denotes a transfer body. The toner image on the transfer member is transferred to a sheet, fixed to the sheet by a fixing mechanism (not shown), and output.

  Reference numeral 130 denotes a paper conveyance path.

  A conceptual diagram of the mechanism 220 is shown in FIG.

  X0˜ and Y0˜ are pixel coordinate inputs in the main scanning direction and the sub-scanning direction.

  The additional information on the printed image requires a certain size that can be read by the magnetic sensor.

  The minimum print pixel of an electrophotographic printer is smaller than the area size suitable for reading with a magnetic sensor, and the toner image itself is not as sharp as it is drawn with the minimum print pixel, and is considerably blurred and widened. .

  Therefore, in order to secure a suitable rectangular area that can be read by the magnetic sensor by collecting some minimum print pixels, and to write information in units of rectangular areas, the coordinate information is encoded and used as determination information for the rectangular area. .

  FIG. 3 shows a layout example of the rectangular area.

  A halftone dot is a rectangular area, and a small square in the background corresponds to the minimum print pixel.

  In this schematic diagram, the horizontal width of the rectangular area is 2 pixels and the vertical length is 12 pixels, and the arrangement period of the rectangular areas is 8 pixels in the horizontal direction and 16 pixels in the vertical direction.

  The actual size and arrangement density of the rectangular area are determined in consideration of the performance of the magnetic sensor for reading and the reading method.

  In the case of a scanning type magnetic sensor, considering that the printing paper is moved in the direction of the arrow, as shown schematically in FIG. It is common to take into account fluctuations.

  Reference numeral 221 denotes a coordinate information encoding means. The input coordinate information is encoded to determine whether it is a rectangular area for writing additional information. If it is within the rectangular area, the output signal is activated.

  In the case of encoding as shown in FIG. 2, the horizontal width of the rectangular area is 8 pixels and the vertical length is 16 pixels, and the arrangement period of the rectangular areas is 64 pixels in the horizontal direction and 32 pixels in the vertical direction.

  222 is an AND gate. The bank information of the lookup table is switched by taking an AND of the judgment information 221 on whether the area is a rectangular area and the write code information of the additional information.

  A selector 223 selects 0/1 of information to be written in the rectangular area by switching the lookup table.

  D0 to are input color information. If the input color information is composed of 6 bits for each RGB, it has 18 inputs, and if it is 8 bits, it has 24 inputs.

  Reference numerals 225 and 226 are lookup tables.

  As shown in this embodiment, when the print color is expressed by four colors of CMYK, when RGB is first replaced with a complementary color and all of CMY are above a certain density value, a certain density value is subtracted from all of CMY, and instead K However, the look-up table performs this at once, and generates CMYK multi-value information from the RGB multi-value information at once by referring to the table.

  However, although not shown in FIG. 2, the table size increases as the gradation steps of the multi-value information increase, so that the lookup table itself stores discrete representative densities, and the intermediate value of the representative density is linear. It may be created by operations such as interpolation.

  FIG. 5 is a graph showing the CMY common density residual value and the K value amount after the CMY common density is replaced with K.

  When the density replacement to K is strongly performed, the characteristics as shown in (A) are obtained, the CMY residual value is small, and the K density amount is large.

  When CMY is left without much density replacement to K, the characteristics as shown in (B) are obtained, the CMY residual value remains considerably, and the density amount of K is small except in a very high density region. .

  That is, drawing a rectangular area with the characteristic (A) has strong magnetism, and drawing a rectangular area with the characteristic (B) does not show much magnetism.

  It is possible to read the embedded additional information by scanning the printed paper with a magnetic sensor and reading whether the rectangular area has the same magnetic characteristics as the neighboring area or different magnetic characteristics as 0/1 information. Become.

  By switching between two look-up tables for performing undercolor removal processing with different K replacement amounts in this way, it is possible to embed bits after encryption redundancy of additional information in a rectangular area.

  Reference numeral 228 denotes additional information supply means.

  Reference numeral 224 denotes redundancy and encryption means.

  The additional information to be embedded is not desirable because it is easily deciphered when it is embedded as it is, and it can be easily decoded.

  For this reason, it is necessary to perform redundancy processing for enhancing the decryptability of the magnetic information itself and encryption that makes it difficult to decrypt the information after reading, because it is difficult to lose information. These processes are performed at 224.

  Reference numeral 227 denotes a code supply control means.

  Since one rectangular area indicates 1-bit information, the same information is surely read out from the rectangular area at the scanning timing of each pixel having a different scanning line or scanning start position, and information converted by 224 is converted. It is necessary to supply to 222.

  In addition, the image information itself to be drawn cannot embed additional information in all places, but when printing text or the like is considered, there are fewer areas to be embedded.

  Therefore, it is necessary to embed the same information over and over again.

  The control means for repeating these embedded information and supplying the same information bits to the rectangular area is 227. From the coordinate information, the corresponding code information on 228 is called and the bit after redundant encryption processing. Control to supply information.

  Image information from an external device or multi-value image information read by a scanner is already rendered in a form in which this rectangular area information is embedded when it is generated as each color image formed in 207 to 210.

  FIG. 4 shows a developed state of the input multi-value gradation image and an image in which additional information is embedded on 207 to 210.

  Although not actually generated, when the outputs of 224 are arranged in accordance with the corresponding pixels, an arrangement like the lookup table switching pattern of FIG. 4 is obtained.

  In accordance with the processing of 224, the rectangular area portion becomes a switching target, or the table is not switched and the same lookup table as the background remains selected.

  In the lookup table switching pattern, the black part is a characteristic table as shown in FIG. 5A, and the white background is a characteristic table as shown in FIG. 5B. The generated K image and CMY image are respectively It becomes like the K enlarged view and CMY enlarged view of FIG.

  Actually, even in the look-up table of FIG. 5B, the replacement amount to K increases in the dark density region, so that K toner is not applied only to the rectangular region as in the enlarged K diagram of FIG. Also K is mixed.

  The enlarged view of K in FIG. 4 is mainly a schematic diagram of the conversion of the light color region, so that the portion where CMY is replaced with K is easy to visually recognize, but the portion where K is replaced with CMY is easy to visually recognize in the dark color region.

  Such CMYK images generated on 207 to 210 are driven by 101 to 104 in accordance with the operation timing of the printing mechanism, developed by an electrophotographic process, and embedded with a magnetic pattern that cannot be grasped visually. Printed out.

The block diagram of the main mechanisms of the 1st Example of this invention is shown. A conceptual diagram of 220 mechanism is shown. A layout example of a rectangular area is shown. An example of developing the input image is shown. An example of CMY background removal characteristics is shown in the graph.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101-104 Optical drive and scanning circuit 105-108 Toner replenishment system 109-112 Photoconductor 120 Transfer body 130 Paper conveyance path 201 Image information and drawing information input means from an external device 202 Scanner 203 Control means for controlling an image processing mechanism 204 Storage means for storing driving procedures of tables and control means 205 Work area memory 220 Conversion table 206 Drawing processor 207 to 210 Page memory 211 to 214 Drive circuit for controlling optical circuit of printing mechanism 221 Coordinate information encoding means 222 AND gate 223 selector 224 redundancy and encryption means 225 and 226 lookup table 227 code supply control means 228 additional information supply means D0 ~ color information input X0 ~ and Y0 ~ pixel coordinate input

Claims (1)

An electrophotographic color print output device using two types of toners, a non-magnetic toner and a magnetic toner,
There is a common area in the color development area generated only with the magnetic toner and the color development area generated only with the non-magnetic toner, and has a mechanism for switching a part of the color conversion table based on the coordinate information and the additional information,
As a means of embedding additional information,
Image processing characterized by using a combination of a minute area in which a drawn image is formed only with the non-magnetic toner and a minute area in which a drawn image is formed only with the magnetic toner in the color gamut of the common region of the color gamut. apparatus.

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