JP2001211322A - Image forming apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that it is difficult to add additional information to an image without causing any degradation in picture quality. SOLUTION: On the basis of a 1st random number sequence held in an initial random number storage part 30 and a machine body information sequence held in a machine body information storage part 302, a random number generation part 303 generates a 2nd random number sequence. A dither processing part 304 holds dither matrixes which are different in dither growing direction, selects one of the dither matrixes according to the 2nd random number sequence, and performs dither processing for input image data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus and an image forming method, and more particularly to an image forming apparatus and an image forming method for embedding additional information in a formed image.

[0002]

2. Description of the Related Art In recent years, the performance of image forming apparatuses such as color printers and color copying machines has been remarkably improved, and higher quality images can be formed.

Under such circumstances, it has become possible to form an image similar to securities such as banknotes by using an image forming apparatus, that is, forgery, and a technique for suppressing such an act is known. ing.

For example, there has been known an addition method for adding a dot pattern indicating a machine number of an image forming apparatus to a color image to be printed out so as to be difficult for human eyes to identify.

[0005] Usually, this dot pattern has a predetermined size, and a plurality of dots are arranged within this predetermined size. The additional information is expressed by the arrangement of the plurality of dots. This dot pattern is periodically added to the entire screen. When a dot pattern is added to a color image composed of a plurality of planes of yellow (Y), magenta (M), cyan (C), and black (K) to make it difficult for human eyes to recognize Is added to only the Y color plane.

When an image for which image formation is prohibited or a copy image for which copying is to be prohibited is found by adding a dot pattern as described above, additional information (machine ), And the device that formed the image can be identified.

[0007]

However, in the above-mentioned conventional dot pattern adding method, even if the Y
Even if a dot pattern is added to a color plane, image quality degradation due to the dot pattern getting in the eyes cannot be avoided.

Further, it is difficult to decipher a dot pattern embedded in a so-called natural image such as a banknote because it is difficult to distinguish the dot pattern from a background image.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and has been made in consideration of the above-described conventional technology. It is an object to provide an apparatus and a method thereof.

[0010]

As one means for achieving the above object, the image forming apparatus of the present invention has the following arrangement.

That is, holding a plurality of dither matrices,
An image forming apparatus comprising dither processing means for performing dither processing based on any of the input image data, a holding means for holding a first random number sequence and a specific information sequence; Random number sequence generating means for generating a second random number sequence based on the specific information sequence, wherein the dither processing means sequentially selects any one of the plurality of dither matrices according to the second random number sequence. It is characterized by the following.

For example, the plurality of dither matrices are:
The dither growth starting points are the same, but the dither growth methods are different from each other.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below in detail with reference to the drawings.

<First Embodiment> An example in which the present embodiment is applied to an image forming apparatus that forms an image using a color electrophotographic technique will be described below. However, the present invention is not limited to this example, and can be applied to an image forming apparatus using an inkjet method, a thermal transfer method, or the like.
The image data input in this embodiment is RG
It is assumed that 8-bit multivalued image data for each color of B is input in parallel.

FIG. 1 is a side sectional view showing the structure of a color laser printer according to the present embodiment. An image processing unit 1000 performs predetermined image processing on an image signal input from a host computer (not shown), and outputs a drive signal of the semiconductor laser 110 corresponding to the image signal as described later. .

Hereinafter, the image forming sequence will be described. First, the photoconductor drum 100 is uniformly charged to a predetermined polarity by the charger 101, and the first latent image of magenta (M) is formed on the photoconductor drum 100 by exposure with the laser beam L emitted from the semiconductor laser 110. An image is formed. Next, in this case, a predetermined developing bias voltage is applied only to the magenta developing device Dm to develop a magenta latent image, and a first magenta toner image is formed on the photosensitive drum 100.

On the other hand, immediately before the transfer paper P is fed at a predetermined timing and the leading end thereof reaches the transfer start position, a transfer bias voltage (+1.8 KV) of the opposite polarity (for example, positive polarity) to the toner is applied to the transfer drum. The first toner image on the photosensitive drum 100 is transferred to the transfer paper P, and the transfer paper P is electrostatically attracted to the surface of the transfer drum 102. Thereafter, the magenta toner remaining on the photosensitive drum 100 is removed by the cleaner 103,
In preparation for a latent image forming and developing step of the next color.

Next, a second latent image of cyan (C) is formed on the photosensitive drum 100 by the laser beam L, and then the photosensitive drum 1 is developed by the cyan developing device Dc.
The second latent image on image No. 00 is developed to form a second toner image of cyan. Then, the cyan second toner image is transferred to the transfer sheet P in accordance with the position of the magenta first toner image previously transferred to the transfer sheet P. This 2
In the transfer of the color toner image, a bias voltage of +2.1 KV is applied to the transfer drum 102 immediately before the transfer paper reaches the transfer portion.

Similarly, the third and fourth latent images of yellow (Y) and black (Bk) are sequentially formed on the photosensitive drum 100, and are sequentially developed by the developing units Dy and Db, respectively. The third and fourth toner images of yellow and black are sequentially transferred in alignment with the toner image previously transferred onto the paper P, and thus the four color toner images are superimposed on the transfer paper P. It is formed.

The transfer paper P on which the four color toner images are superimposed is
After being separated from the transfer drum 102 and fixed by being heated and pressurized by a fixing device 104, the toner is discharged outside the apparatus.

Reference numeral 107 denotes an operation unit which includes operation buttons, a display panel, predetermined LEDs, and the like, and notifies the status of the apparatus and inputs an instruction by a user.

FIG. 2 is a block diagram showing the flow of image data in the image processing section 1000. The 8-bit RGB data 201 is first input to the color conversion processing unit 202 and subjected to LOG conversion, masking, UCR, and other processing, thereby being converted into 8-bit CMYK data. The CMYK data is input to the gamma correction unit 203, and is converted by a gamma correction table so that the output gamma is optimized for each color. The gamma-corrected data is then input to the halftone processing unit 204, binarized by dither processing described later, and stored in the buffer 205. Thereafter, data for one screen is sequentially transmitted in the order of C, M, Y, and K, converted into an analog signal by the D / A converter 206, and input to the laser driver 207.

FIG. 3 shows a detailed block configuration of the halftone processing unit 204. The halftone processing unit 204 includes an initial random number storage unit 301, a machine information storage unit 302, a random number generation unit 303, a dither processing unit 304, a horizontal line counter 305, and a vertical line counter 306.

The initial random number storage unit 301 stores a fixed initial random number sequence in advance. Here, an example of the initial random number sequence is shown in FIG. As shown in the figure, the initial random number sequence is composed of nine random numbers, and each random number takes any value of 0 to 3.

In the machine information storage unit 302, information strings relating to the printing environment such as machine number, manufacturer name, print date and time are encrypted and stored as a combination of 0 to 3 values. FIG. 4B shows an example of the stored machine information sequence.
As shown in the figure, the machine information sequence is composed of nine values, like the initial random number sequence. Therefore, the machine information sequence that can be represented in the present embodiment has 49 information amounts.

[Information Adding Process] Hereinafter, a process of embedding additional information in an input image in the present embodiment will be described.

At power-on or printing, the random number generation unit 303 adds the initial random number sequence and the machine information sequence, and
By calculating d4 (residue of division by 4), a new random number sequence is generated. An example of this new random number sequence is shown in FIG.
It is shown in (c).

Further, by inserting 4 into the first, second and fourth random number sequences thus generated, a total of 12
A random number sequence is created and stored in the random number generation unit 303 as a 3 × 4 random number matrix. An example of this random number matrix is shown in FIG.
Shown in Therefore, only the upper left three elements of the random number matrix are
Would have a value of 4.

As described above, the random number matrix in the present embodiment is represented by the general format shown in FIG.

At the time of printing, the number of horizontal lines of the image is counted by the horizontal line counter 305, and the count value HCNT is subjected to the calculation of mod18. And if the operation result is 0 to 5, the first column of the random number matrix,
If it is 6 to 11, the second column of the random number matrix is selected, and if it is 12 to 17, the third column of the random number matrix is selected.

On the other hand, the vertical line counter 306 counts the number of vertical lines of the image,
The operation of mod 24 is performed on NT. If the calculation result is 0 to 5, the first row of the random number matrix is 6 to 11; the second row of the random number matrix is 12 to 17; For example, the fourth row of the random number matrix is selected.

Therefore, the horizontal and vertical line counters 30
By 5,306, r ₀₀ ~r from the random matrix shown in FIG. 5
₃₂ is selected, and the value of the selected element (each element value shown in FIG. 4D) is dithered as a 3-bit random number signal (indicating any value of 0 to 4). Processing unit 3
04 is input.

The dither processing unit 304 has the configuration shown in FIGS.
The five dither matrices shown in (e) (hereinafter referred to as dither matrices A to E) are stored.
Numbers in matrix are dither growth order (threshold)
And 0 is the lowest threshold. Each of these dither matrices has 100 lines / inch and a screen angle of 0 degree.

These dither matrices A to E are designed so that the method of starting the growth of halftone dots is different from each other.
For example, in a concentration region having an area ratio of 25%, FIG.
Halftone dots as shown in (a) to (e) are formed. As can be seen from FIG. 7, the dither matrix A forms a halftone dot of spiral growth. Similarly, the dither matrix B grows vertically,
C forms halftone dots of lateral growth, D forms oblique left growth, and E forms oblique right growth.

The dither processing unit 304 selects a matrix according to the 3-bit random number signal input from the random number generation unit 303 as described above. Specifically, matrices B, C, D, E, and A are respectively selected according to which of the random number signals is 0, 1, 2, 3, and 4, and the input image is based on the matrices. Dithering is performed. Thereby, the machine information is added to the input image.

The image after the dither processing based on the random number matrix shown in FIG.
A set of halftone dots having a size of 4 (hereinafter referred to as a halftone matrix) repeatedly appears. In the upper left three halftone dots in the halftone dot matrix shown in FIG. 8, the spiral growth dither by the matrix A is always selected. Therefore, these three points function as marks indicating the beginning of the dot matrix. Hereinafter, a set of three halftone dots indicating the beginning of such a halftone matrix will be referred to as a reference halftone dot,
The positions of these three halftone dots are called reference positions.

Information Decoding Process In this embodiment, the machine information is added to the input image as described above, and an image based on the image data to which the information has been added is formed on the recording medium. Therefore, at the time of decoding the additional information, first, the image data is read by reading the recording medium with a scanner or the like, and the image data is masked at the reference position as shown by a rectangle in FIG. Can be recognized, and the beginning of the dot matrix can be specified.

Next, by looking at the shape of each dot in the dot matrix, if longitudinal growth 0, if the lateral growth 1, and so on left oblique growth if 2, if the right diagonal growth 3, r ₀₀ ~ it is possible to determine the value of r _42. If each halftone dot corresponds to any one of r ₀₀ to r ₄₂ , machine information can be calculated by performing an inverse calculation based on these values and a known initial random number sequence. That is, the specific information added at the time of printing can be obtained.

As described above, according to the present embodiment,
When embedding the additional information in the input image, the dither growth method is varied in a random manner to embed the additional information in the random number, so that a decodable signal can be reliably embedded without deteriorating the image quality. It becomes possible.

In this embodiment, an example in which the dither matrix having the same number of lines and the same screen angle is used for each color has been described. However, a dither matrix having a different number of lines and a different screen angle for each color may be used.

In this embodiment, the number of initial random numbers and the number of values indicating machine information have been described as the same number. However, for example, the number of initial random numbers is set to an integral multiple of the number of values indicating machine information.
The two numbers do not necessarily have to match.

Further, the processing of this embodiment may be performed only for a specific color, and a dither matrix may be selected for other colors in accordance with an initial random number sequence.

Further, in this embodiment, by vibrating the halftone dot shape in a random manner, it is effective to prevent moire for each color. Furthermore, in order to improve image quality, the number of random numbers may be increased to increase the halftone dot matrix, and random numbers having characteristics of so-called white noise or blue noise may be applied.

<Second Embodiment> Hereinafter, a second embodiment according to the present invention will be described.
An embodiment will be described.

The configuration of the device according to the second embodiment is the same as that of the first embodiment described above.

The initial random number sequence in the second embodiment is shown in FIG.
As shown in (a), it consists of six random numbers, each random number being 0,
It takes one of four values of 1, 2, and 3. Similarly, the machine information to be added to the input image also includes six values as shown in FIG. 9B, and each value takes one of four values of 0, 1, 2, and 3.

Hereinafter, a process of embedding additional information in an input image in the second embodiment will be described.

At power-on or printing, the random number generation unit 303 adds the initial random number sequence and the machine information sequence, and
By calculating d4 (residue of division by 4), a new random number sequence is generated. FIG. 9 shows an example of this new random number sequence.
It is shown in (c).

The random number matrix in the second embodiment is shown in FIG.
And the values of the 0th and 1st rows of the random number matrix are r ₀₀ = r ₀₁ = r ₁₀ = 1,
_{r 02 = r 03 = r 11} = r 12 = r 13 = 0, take a fixed value and so on. Further, in the second and subsequent rows of the random number matrix, only one of the four elements in each row becomes 1, and the remaining three take 0, and which element becomes 1 is shown in FIG. 9C. Follow a sequence of random numbers. In the random number sequence shown in FIG. 9C, the position of the element that becomes 1 in the second row of the random number matrix, the random number matrix 3
The position of the element to be 1 in the row is sequentially represented. That is, FIG.
According to the random number sequence of (c), the second element from the left is 1 for the second row of the random number matrix, the second element from the left is 1 for the third row, and so the random number matrix is 1
As shown in FIG.

The dither processing unit 304 includes two dither matrices (hereinafter, referred to as dither matrices A and B) of a spiral growth dither shown in FIG. 12A and a vertical growth dither shown in FIG. 12B. Is stored. The numbers in each of these dither matrices represent the dither growth order (threshold) as in FIG.

At the time of printing, the number of horizontal lines of the image is counted by the horizontal line counter 305, and the count value HCNT is subjected to the calculation of mod24. And if the operation result is 0 to 5, the first column of the random number matrix,
6 to 11, the second column of the random number matrix; 12 to 17, the third column of the random number matrix;
The row is selected.

On the other hand, the vertical line counter 306 counts the number of vertical lines of the image, and the counted value VC
The operation of mod 48 is performed on NT. If the calculation result is 0 to 5, the first row of the random number matrix is 6 to 11; the second row of the random number matrix is 12 to 17; The fourth row of the random number matrix, 24
If it is ~ 29, it is the fifth row of the random number matrix; if it is 30-35, it is the sixth row of the random number matrix; if it is 36-41, it is the seventh row of the random number matrix; Is selected.

Therefore, the horizontal and vertical line counters 30
By 5,306, r ₀₀ ~ from the random matrix shown in FIG. 10
r ₇₃ is selected, and the value of the selected element (each element value shown in FIG. 11) is converted to a dither processing unit 3 as a 1-bit random number signal (indicating either 0 or 1).
04 is input.

In the dither processing section 304, the random number generation section 30
A matrix is selected in accordance with a 1-bit random number signal input from 3. Specifically, if the random number signal is 0, the matrix A is selected, and if the random number signal is 1, the matrix B is selected, and the input image is subjected to dither processing based on the matrix. Thereby, the machine information is added to the input image.

The image after the dither processing based on the random number matrix shown in FIG. 11 has 32 pixels as shown by a rectangle in FIG.
A 4 × 8 halftone matrix including the halftone dots repeatedly appears.
In the upper left three halftone dots in the halftone dot matrix shown in FIG. 13, the spiral growth dither by the matrix A is always selected. Therefore, these three points function as a mark indicating the beginning of the dot matrix, that is, a reference dot.

In the second embodiment, the machine information is added to the input image as described above, and an image based on the image data to which the information is added is formed on the recording medium. Therefore, when decoding the additional information, first, the image data is read by reading the recording medium with a scanner or the like, and a set of vertically growing halftone dots constituting a reference halftone dot is detected for the image data. , A dot matrix can be specified. Next, by examining the position of the vertically growing halftone dot in the halftone dot matrix, the value of the original random number sequence (FIG. 9C) can be specified. Thereafter, the specific information added at the time of printing can be obtained by the same method as in the first embodiment described above.

As described above, according to the second embodiment, even when a smaller initial random number sequence and a smaller number of types of dither matrices are used than in the above-described first embodiment, the same effect as in the first embodiment is obtained. The technique makes it possible to embed a decodable signal without deteriorating the image quality.

Incidentally, it is of course possible to execute the first embodiment and the second embodiment in combination.

The present invention is not limited to the case where specific information for forgery tracking is added to image data.
For example, the case where the name of the creator who created the original image or the name of the work of the image is used as the additional information is also included in the present invention.

<Other Embodiments> The present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), and the present invention can be applied to an apparatus (one device). For example, the present invention may be applied to a copying machine, a facsimile machine, and the like.

Further, an object of the present invention is to supply a storage medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and a computer (a computer) of the system or the apparatus. It is needless to say that the present invention can also be achieved by a CPU or an MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. Also,
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also the operating system (OS) running on the computer based on the instructions of the program code.
It goes without saying that a case where the functions of the above-described embodiments are implemented by performing some or all of the actual processing, and the processing performs the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written in the memory provided in the function expansion card inserted into the computer or the function expansion unit connected to the computer, the program code is read based on the instruction of the program code. Needless to say, the CPU included in the function expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0063]

As described above, according to the present invention, when additional information is added to an image, the decoding of the additional information can be performed more reliably without deteriorating the image quality.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a color laser printer according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a flow of data in an image processing unit.

FIG. 3 is a block diagram illustrating a detailed configuration of a halftone processing unit.

FIG. 4 is a diagram illustrating an example of a random number sequence according to the embodiment.

FIG. 5 is a diagram illustrating a random number matrix according to the present embodiment in a general format.

FIG. 6 is a diagram illustrating an example of a dither matrix according to the present embodiment.

FIG. 7 is a diagram illustrating a growth method for each dither matrix in the embodiment.

FIG. 8 is a diagram illustrating an example of a halftone matrix generated in the present embodiment.

FIG. 9 is a diagram illustrating an example of a random number sequence according to the second embodiment of the present invention.

FIG. 10 is a diagram showing a random number matrix in a general form according to the second embodiment.

FIG. 11 is a diagram illustrating an example of a random number matrix according to the second embodiment.

FIG. 12 is a diagram illustrating an example of a dither matrix according to the second embodiment.

FIG. 13 is a diagram illustrating an example of a halftone matrix generated in the second embodiment.

[Explanation of symbols]

 301 Initial random number storage unit 302 Aircraft information storage unit 303 Random number generation unit 304 Dither processing unit 305 Horizontal line counter 306 Vertical line counter

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Claims (15)

[Claims] 1. An image forming apparatus comprising: a plurality of dither matrices; and dither processing means for performing dither processing on input image data based on any one of the plurality of dither matrices. Holding means for holding, and random number sequence generating means for generating a second random number sequence based on the first random number sequence and the specific information sequence, wherein the dither processing means comprises: An image forming apparatus for sequentially selecting any one of the plurality of dither matrices according to the following. 2. The image forming apparatus according to claim 1, wherein the plurality of dither matrices have the same dither growth start point but different dither growth methods. 3. The image forming apparatus according to claim 1, wherein the dither processing unit selects a dither matrix according to the second random number sequence based on a pixel position of the input image data. 4. The image forming apparatus according to claim 1, wherein the first random number sequence is set in the image forming apparatus in advance. 5. The image forming apparatus according to claim 1, wherein the specific information sequence indicates identification information for specifying the image forming apparatus. 6. The image forming apparatus according to claim 1, wherein said random number sequence generating means generates said second random number sequence based on addition of said first random number sequence and said specific information sequence. apparatus. 7. The image forming apparatus according to claim 1, wherein the dither processing means performs dither processing on all color components of the input image data. 8. The dither processing means selects a dither matrix for a predetermined color component of the input image data based on the second random number sequence, and selects the first dither matrix for a color component other than the predetermined color component. 2. The image forming apparatus according to claim 1, wherein a dither matrix is selected based on a random number sequence of the following. 9. The image forming apparatus according to claim 1, wherein the dither processing unit selects a different dither matrix for each color component of the input image data. 10. The image forming apparatus according to claim 1, wherein the dither processing unit selects a dither matrix common to all color components of the input image data. 11. The first random number sequence is composed of a finite number of random numbers, and the random number sequence generation means generates the second random number sequence by repeatedly reading the first random number sequence. The image forming apparatus according to claim 1. 12. The image forming apparatus according to claim 11, wherein the first random number sequence is configured by a random number that is an integral multiple of the number of elements constituting the specific information sequence. 13. The image forming apparatus according to claim 1, further comprising forming means for forming an image based on the image data after the dither processing by the dither processing means. 14. An image forming method in an image forming apparatus holding a plurality of dither matrices, wherein a second random number sequence is generated based on a first random number sequence and a specific information sequence. And sequentially selecting any of the plurality of dither matrices according to the following formula, and performing dither processing on the input image data based on the selected dither matrix. 15. A recording medium recording a program of an image forming process in an image forming apparatus holding a plurality of dither matrices, the program comprising at least a second random number sequence and a second information sequence based on a specific information sequence. A code for generating a random number sequence, a code for sequentially selecting any of the plurality of dither matrices according to the second random number sequence, and a dither based on the selected dither matrix for input image data. And a code for performing processing.