JP3472210B2 - Image processing method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and apparatus for adding a code pattern indicating additional information to multivalued input image information.

[0002]

2. Description of the Related Art In recent years, image quality of color printers, color copiers and the like has been improved, and it has become possible to easily reproduce an original image as a printed matter and faithfully reproduce it. Therefore, securities such as banknotes can be easily forged, and various measures have been taken.

[0003] Conventional methods for preventing forgery are roughly classified into a method of recognizing that an original is securities and not performing faithful printing, and a machine number of a printing device in a printed matter. By adding it, it can be classified into a method for identifying the aircraft used when the securities were forged.

Particularly, the latter technique, which is the technique of multiplexing the machine identification information on the image information, not only prevents the forgery of securities, but also protects copyright, protects confidential information, and protects characters,
It is also applied to a transmission method of voice and the like, and various methods have been proposed.

For example, regarding the shape of a code representing information, as described in Japanese Patent Laid-Open No. 10-304179, a method of adding a dot pattern composed of a plurality of regions having different longitudinal directions as a code has been proposed. .

[0006]

However, the above-mentioned conventional multiplexing method has the following problems.

The reference numerals described in Japanese Patent Application Laid-Open No. 10-304179 have a shape having a specific longitudinal direction. Therefore, for example, when pseudo gradation processing is performed on the image information by the error diffusion method, adding this code will cause continuous dot arrangement in a specific direction to appear in the highly dispersive dot arrangement peculiar to the error diffusion method. To do. Therefore, the code is easily visually recognized, and the image quality is deteriorated.

When the identification information is added to prevent forgery, it is necessary to arrange an information block composed of a plurality of codes in the entire image. As a result, the arrangement of the codes tends to be regular, which makes it easier to visually recognize the codes and deteriorates the image quality.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to realize a multi-valued image without deterioration of image quality .
A code pattern indicating additional information is added to the input image information .
It is an object of the present invention to provide an image processing method and device that can be added .

[0010]

As one method for achieving the above object, the image processing method of the present invention comprises the following steps.

That is, it is an image processing method for adding a code pattern indicating additional information to multi-valued input image information, wherein the darkness of the peripheral region of the pixel of interest in the input image information .
Based on the time, the code path to be added from a plurality of code patterns
A setting step of setting a turn, based on the set code pattern <br/>, code patterns for the input image information
A determination step of determining a quantization threshold value of the target pixel to be added, and having a quantization step of quantizing the pixel of interest based on the determined quantization threshold.

For example, the quantization step is characterized in that quantization is performed by pseudo gradation processing.

For example, the quantization step is characterized by performing quantization by an error diffusion method.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to the drawings.

<First Embodiment> FIG. 1 is a block diagram showing the arrangement of an image processing apparatus according to the present embodiment. For example, the image processing apparatus is applied to a printing apparatus such as an inkjet printer which forms an image using pseudo gradation expression. it can.

In the figure, reference numeral 100 is an input terminal for inputting image information, and 101 is an input terminal for inputting additional information such as identification information. Reference numeral 102 denotes a quantization condition determination unit that determines a quantization condition when quantizing image information. The quantization condition determining unit 102 holds a plurality of quantization conditions as a table in an internal ROM (not shown) or the like,
An appropriate quantization condition is selected from there. Reference numeral 103 is a code pattern memory that holds a plurality of types of dot patterns that represent one code that constitutes additional information, and the held code patterns are referenced when the quantization condition determination unit 102 determines the quantization condition. It A quantization unit 104 quantizes the image information, and quantizes the image information by a method such as an error diffusion method based on the quantization condition determined by the quantization condition determination unit 102. Also, 105 is an output terminal for outputting the quantized image information.

The error diffusion method is a method in which multi-valued image information is expressed in pseudo gradation by a binary value or a quantization value smaller than the input image information, and when the pixel value of interest is quantized. Is a quantization method for preserving image density by distributing the error generated in 1 to the pixels around the pixel of interest.

FIG. 2 shows an example of the error distribution matrix of the error diffusion method. In FIG. 2, * represents the position of the pixel of interest, and a to
l represents the distribution ratio of the quantization error generated in the target pixel, and distributes the error according to the distribution ratio to the pixels around the target pixel. In the example shown in FIG. 2, the error is distributed in the range of 2 pixels both vertically and horizontally from the pixel of interest, but the error distribution range is not limited to this. In this embodiment, it is assumed that the vertical code addition interval is constant and the horizontal code addition interval is changed.

FIG. 3 is a flow chart showing the control procedure of code addition in this embodiment.

First, in step S300, a variable i for counting vertical addresses and a variable j for counting horizontal addresses are initialized. Step S
At 301, it is determined whether or not a code is added to the row indicated by the row address i. If it is the row to which the code is added, it is determined in step S302 whether the code is added to the column indicated by the column address j.

When it is determined in steps S301 and S302 that the pixel of interest indicated by the addresses i and j is the code addition position, the process proceeds to step S303.
In the present embodiment, since the additional code is represented by the code pattern having a predetermined arrangement of a plurality of dots, in step S303, the coordinate value of the pixel of interest in the code pattern is calculated based on the coordinate value (i, j) of the pixel of interest. Is calculated, and the image density d around the target pixel (i, j) is detected in step S304.

The code pattern in this embodiment is
It is set according to the code addition target image from the plurality of dot patterns held in the code pattern memory 103. This code pattern is set before the code addition process is started, and the setting method will be described later.

In step S305, the quantization condition determining unit 102 sets a plurality of quantization conditions in advance for adding the code based on the image density d around the pixel of interest, the code value in the code pattern, and the additional information. Obtained from the table in which the quantization conditions are registered. Then, in step S306, pseudo gradation processing (quantization processing in the quantization unit 104) is performed on the image information. By this pseudo gradation process, substantial sign addition in the present embodiment is performed.

On the other hand, if it is determined in step S301 or S302 that the pixel position is not the pixel position to which the code is added, the process proceeds to step S307 to acquire the normal quantization condition in which the code is not added, and then to step S306. The pseudo gradation process is performed on the image information.

Then, in step S308, the count value of the column address j is incremented by 1, and in step S309, it is determined whether or not the processing in the column direction is completed. If not completed, the process returns to step S302, but if completed, the process proceeds to step S310.

After the column address j is initialized in step S310, the count value of the row address i is incremented by 1 in step S311, and it is determined in step S312 whether the processing has been completed for all rows. If the process is not completed in step S312, S30
Returning to 1, if all the processing is completed, the code addition processing is completed.

FIG. 4 shows an example of an information block showing 4-bit information added to the image information in this embodiment. In the figure, “●” indicates one code, that is, a code pattern including a plurality of dots.

In FIG. 4, the information bit is represented for each code addition line in the image information according to the interval of the additional code. According to the figure, the code interval in the same row is constant, and the information bit is "1" when the code interval corresponds to an odd number of the code and the information bit "0" when it corresponds to an even number. Indicates. That is, the information block is “1010”.
4 bit information is shown.

In the anti-counterfeiting technique or the like which requires reliable detection of the additional information from the image, that is, the information block shown in FIG. 4 is embedded in every place of the entire image information. Note that the information blocks shown in FIG. 4 merely show one embodiment of the present invention, and the present invention is not limited to this embodiment and is applied.

In general, when a code indicating specific information is added to an image expressed in pseudo gradation, the image quality is deteriorated because the code is visually recognized. However, especially when adding a code as a security counterfeit prevention measure,
In order to reliably detect the added specific information, it is necessary to add the code repeatedly over a wide range in the image. Therefore, it is necessary that the code itself is not easily visible.

As one of the methods of making the code less visible, there is a method of using a code having a small size.
However, this method is not practical because not only a high-resolution reading function is required in the image reading device used at the time of code detection, but also the optimum reading resolution differs for each printing device.

Therefore, it is conceivable that the code has a pattern shape that is hard to be visually recognized. However, the dot arrangement of the image expressed in the pseudo gradation greatly depends on the pseudo gradation processing method. For example, when performing pseudo gradation processing by the error diffusion method, if the error distribution ratio in the error distribution matrix shown in FIG. 2 is changed, the dot arrangement of the output image is changed. Also,
As the dot arrangement of the output image in the window of a certain fixed size, many specific patterns appear, especially in the case of an image flat portion composed of characters and the like.
There is a feature that another specific pattern does not appear. Furthermore, the appearance rate of the pattern also depends on the density of the image,
A pattern that does not appear at a certain density may appear at another density.

Here, the code pattern and its addition process used in the present embodiment will be specifically described in view of the above characteristics in the pseudo gradation process by the error diffusion method.

First, the code pattern in this embodiment will be described with reference to FIGS.

FIGS. 5 (a) and 5 (b) show flat images having densities of about 2% (5/256) and about 6% (15/256), respectively, which are binarized by the error diffusion method. It is a figure which shows a part. Further, FIG. 6 shows a 5 × 5 size dot pattern window, which is 500 in FIG.
The arrangement pattern of dots appearing in the portion indicated by is shown. It can be seen that the pattern shown in FIG. 6 does not appear in FIG.

Therefore, in the present embodiment, FIG.
For the image density (about 2%) corresponding to, the pattern shown in FIG. 6 is set as a code (hereinafter, code pattern) distinguishable from the image information. That is, the code pattern memory 10
Among the plurality of code patterns held in the No. 3, the flattened image with a density of 2%, the pattern shown in FIG. 6 is selected by the quantization determination unit 102. The code pattern stored in the code pattern memory 103 is a pattern that can appear in the quantization result of the flat portion having a certain density. Therefore, in this embodiment, a natural dot pattern can always be set as the code pattern.

Here, FIG. 7 shows an example of the configuration of the threshold value for creating the code pattern shown in FIG. 6 when performing the pseudo gradation expression using the error diffusion method. Since the accumulated error in the error diffusion method falls within a predetermined range, it is possible to always turn on the dot corresponding to the threshold value by setting the threshold value for binarization to a certain value or less. Therefore, in the pixel block shown in FIG. 7, threshold values are set so that dots corresponding to pixels at the four corners are always turned on, and threshold values during normal processing are set for Y corresponding to other pixels. To set. Figure 7 created in this way
With the threshold block of, the code pattern shown in FIG. 6 can be reliably created.

Next, with reference to FIG. 8, an example in which the code pattern according to the present embodiment is actually added to an image will be specifically described.

In FIG. 8A, the code pattern shown in FIG. 6 is applied to the images having the same density as in FIG.
It is a figure which shows the example of the output image which added as 1,802,803 and binarized.

In FIG. 8B, a pattern different from the code pattern shown in FIG. 6 is added to the image having the same density as that in FIG. It is a figure which shows the example of the output image which performed the process. These patterns 804 to 807 have the same number of dots as the code pattern shown in FIG. 6 (reference numerals 800 to 803 shown in FIG. 8A), but their shapes are different, and are flat during normal binarization processing. It is a pattern that does not appear in the section.

According to FIGS. 8A and 8B, the code patterns (codes 800 to 80) set in this embodiment are used.
It can be seen that 3) is less visible. That is, by setting a pattern that is difficult to be visually recognized in the flat portion of the density as the code pattern, it is possible to suppress the image quality deterioration when the code is added.

In the present embodiment, an example has been described in which the dot pattern shown in FIG. 6 does not appear in the density of FIG. 5A, and this is used as the code pattern. However, in an actual image, a perfect flat portion does not always exist, and fluctuations in pixel values may exist in each region. Therefore, when actually setting the code pattern, it is necessary to confirm that the pattern does not appear not only in the target density range but also in the surrounding density range.

In the present embodiment, the density in the window forming the code pattern shown in FIG. 6 is as shown in FIG.
It is higher than the average density of the image shown in. In general,
In a pattern that does not appear at a certain density and appears at another density, the density within that window is often significantly different from the target image density. Therefore, as the code pattern in the present embodiment, it can be considered that the density within the window is higher or lower than the target image density, but if the target image density is low, the code pattern within the window When the density of the target image is higher than the density of the target image, conversely, when the density of the target image is high, the density in the window of the code pattern is set lower than the density of the target image. Specifically, the number of dots that are on or off in the code pattern, whichever is smaller, may be larger than the number of dots that appear as a result of quantization of the target image. As a result, it is possible to prevent the code pattern from being buried in the dot arrangement forming the image and becoming difficult to detect.

In this embodiment, the case where the code pattern has a window size of 5 × 5 as shown in FIG. 6 has been described. However, the window size is not limited to this, and the window aspect ratio is the same. You don't have to. That is, it goes without saying that the code pattern shown in FIG. 6 is merely one embodiment, and the present invention is not limited to this.

Further, since the dot pattern that appears by binarization changes according to the image density, it is possible to set a code shape that is less visible by making the code pattern variable according to the image density. Become. Of course, it is also effective to change the window size of the code pattern according to the image density.

As described above, according to this embodiment,
In particular, when heterogeneous information is multiplexed in image information in which image information having many flat portions is expressed in pseudo gradation, it is possible to suppress image quality deterioration by making the code shape expressing the information less visible.

<Second Embodiment> The second embodiment of the present invention will be described below.
An embodiment will be described.

The second embodiment is characterized in that the code shape is changed for each color component when the code is added to the color image.

Generally, in a printing apparatus such as an ink jet printer or a color laser printer, a color image is printed by using C (cyan), M (magenta), Y (yellow), K (black) ink or toner. I do. When such color printing is performed, even if the same shape is formed, the visual impression differs depending on the color components. For example, considering the case of printing dots on white paper, when K ink is used, it is visually noticeable, but when Y ink is used, it is less noticeable.

Here, in order to prevent the forgery of securities, when adding information such as the machine number of the printed product, the additional information must be detected reliably. One of the methods of adding a large amount of information to as few areas as possible is a method of dividing and adding information to a plurality of color components. In order to perform reliable information detection regardless of the image, it is effective to add information to a plurality of color components and increase the information readable condition as described above.

However, due to the visibility of the ink colors as described above, the code may be conspicuous depending on the color even if the code of the same shape is added to each color.

In view of this, the second embodiment is characterized in that when a code is added to a color image, the shape of the code pattern is controlled according to the visibility of dots for each color component. That is, the more easily the color component is visually recognized, the more difficult it is to be visually recognized than the efficiency of code addition, and the code pattern shape is determined.

It is also effective to change the size of the code pattern for each color component.

The code pattern shape in the second embodiment may be set by the same method as in the above-described first embodiment.

As described above, according to the second embodiment, by controlling the code pattern shape in consideration of the visibility of the color component to which the code is added, it is possible to reduce the image quality deterioration in the color image. .

<Third Embodiment> The third embodiment of the present invention will be described below.
An embodiment will be described.

In the above-described first embodiment, an example in which the code patterns are multiplexed especially in the flat portion of the image has been described. However, the actual image information may include an edge portion. In particular, when a code is added for the purpose of preventing the forgery of securities, the image to be added includes characters, pictures, patterns, etc., that is, there are many edge portions. Therefore, in order to reliably read the additional information, it is desired that the code pattern can be detected even at the edge portion.

Therefore, in the third embodiment, the shape control of the code pattern at the edge portion will be described.

The code pattern used on the low density side of the edge portion has only the density of dots that is scattered in the low density area. Therefore, for example, when the code pattern is buried in the edge portion and only about half of it can be detected in the edge portion, it is possible to determine whether or not the detected dot indicates the code pattern, that is, the code. It will be difficult. Similarly, on the high density side of the edge portion, if the code pattern is composed of dispersed dots, similarly, it will be difficult to detect the code.

Therefore, the third embodiment is characterized in that the code pattern is set so that the edge portion of the image can be surely detected.

FIG. 9 shows an example in which a code is added to the edge portion of the image. In the figure, 900, 901, 9
Reference numeral 02 denotes a code added respectively, and reference numeral 900 denotes a code which is difficult to be visually recognized in the low density region under the quantization condition, like the code 800 and the like in the first embodiment described above. On the other hand, reference numerals 901 and 902 denote the codes relating to the edge portion, which is a feature of the third embodiment.

FIG. 10 shows an example of code patterns corresponding to codes 901 and 902. According to the figure, that is, it can be seen that a pattern having a low dot dispersibility, that is, a dense dot pattern is set as a code particularly related to the edge portion.

Further, it is also very effective to increase the size of the code pattern in order to reliably discriminate the code even when only a part of the code pattern is detected. It is also effective to set the code pattern in consideration of the edge shape.

As described above, according to the third embodiment,
Especially when adding a code to the edge part of an image, by setting a code pattern in which dots are densely set, the code can be reliably identified even if only a part of the code pattern is detected. It becomes possible to do.

[0065]

Other Embodiments Even when the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus including one device (for example, a copying machine). Machine, facsimile machine, etc.).

Further, an object of the present invention is to supply a storage medium (or a recording medium) recording a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and a computer of the system or the apparatus ( Needless to say, this can also be achieved by the CPU or MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Also,
By executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instructions of the program code.
Needless to say, this also includes the case where the above-mentioned processes perform part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

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

When the present invention is applied to the above storage medium, the storage medium stores the program code corresponding to the flowchart shown in FIG. 3 described above.

[0069]

As described above, according to the present invention, it is possible to add a code pattern indicating additional information to multi-valued input image information without causing image quality deterioration. Become.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an image processing apparatus according to an embodiment of the invention.

FIG. 2 is a diagram showing an error distribution matrix in the present embodiment,

FIG. 3 is a flowchart showing a code addition control procedure in the present embodiment,

FIG. 4 is a diagram showing an example of an information block added in the present embodiment,

FIG. 5 is a diagram showing an example of binarization of a flat image in the present embodiment,

FIG. 6 is a diagram showing an example of a code pattern in the present embodiment,

FIG. 7 is a diagram showing an example of a threshold value for code generation in the present embodiment,

FIG. 8 is a diagram showing an example of code addition in the present embodiment;

FIG. 9 is a diagram showing an example of adding a code to an edge portion in the third embodiment;

FIG. 10 is a diagram showing an example of a code pattern of an edge portion in the third embodiment.

[Explanation of symbols]

100 Image information input terminal 101 Additional information input terminal 102 Quantization condition determination unit 103 code pattern memory 104 quantizer 105 Image information output terminal

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-23333 (JP, A) JP-A-11-32202 (JP, A) JP-A-11-27530 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H04N 1/38-1/393

Claims (17)

(57) [Claims] 1. An image processing method for adding a code pattern indicating additional information to multi-valued input image information, wherein a plurality of code patterns are provided based on a density of a peripheral region of a pixel of interest in the input image information . Code pattern added from
A setting step of setting a down, based on the set code pattern, a determination step of determining a quantization threshold value of the pixel of interest such that the code pattern is added for the input image data was determined quantized And a quantization step of quantizing the pixel of interest based on a quantization threshold value . 2. The image processing method according to claim 1, wherein in the quantization step, quantization is performed by pseudo gradation processing. 3. The image processing method according to claim 2, wherein in the quantization step, quantization is performed by an error diffusion method. 4. The image processing method according to claim 1, wherein the density is a density in a flat portion. 5. The code pattern is composed of a plurality of dots .
The image processing method according to claim 1, wherein the indicating the that pattern. 6. The code pattern in the setting step.
6. The image processing method according to claim 5, wherein the screen is selected from a plurality of dot patterns prepared in advance. 7. The dot pattern prepared in advance can appear as a quantization result in the quantization step in a flat portion of the input image information. Image processing method. 8. The image processing method according to claim 6 , wherein in the setting step, a dot pattern that does not appear as a result of the quantization is selected in a uniform flat image based on an average pixel value around the target pixel. . 9. In the setting step, a dot pattern having a smaller number of dots, on or off, than the dot pattern appearing as the result of the quantization in the uniform flat image is selected. The image processing method according to claim 8. 10. The method further comprises a color component detection step of detecting a color component to be coded in the input image information, wherein the setting step selects the dot pattern based on the color component of the input image information. The image processing method according to claim 6, further comprising: 11. The image processing method according to claim 10, wherein in the setting step, the size of the dot pattern is set based on the color component. 12. The method further comprises an edge detection step of detecting an edge portion of the input image information, and in the setting step, the dot pattern is selected depending on whether or not the periphery of the pixel of interest includes the edge portion. The image processing method according to claim 6, wherein. 13. In the setting step, the first dot pattern is selected when the periphery of the pixel of interest does not include the edge portion, and when the edge portion includes the edge portion, the dot arrangement is made to be higher than that of the first dot pattern. 13. The image processing method according to claim 12, wherein a second dot pattern having a high density is selected. 14. An image processing apparatus for adding a code pattern indicating additional information to multi-valued input image information, comprising: holding means for holding a plurality of code patterns, and a periphery of a pixel of interest in the input image information . based on the code pattern selected from said holding means based on the concentration in the region, the code pattern is added for the input image information
The image processing apparatus according to claim determination means for determining the quantization threshold value of the target pixel as a quantization means for quantizing the pixel of interest based on the determined quantization threshold, to have a. 15. The image processing apparatus according to claim 14, wherein the quantization unit performs quantization by pseudo gradation processing. 16. The image processing apparatus according to claim 15, wherein the quantization means performs quantization by an error diffusion method. 17. A code pattern for indicating additional information to multivalued input image information in a computer.
An image processing method for adding a code pattern , wherein the code pattern is added from a plurality of code patterns based on a density of a peripheral region of a pixel of interest in the input image information .
A setting procedure for setting down, based on the set code pattern, a determination procedure for determining the quantization threshold value of the pixel of interest such that the code pattern is added for the input image data was determined quantized A computer-readable recording medium recording a program for executing a quantization procedure of quantizing the pixel of interest based on a quantization threshold .