JP2001103285A - Image processing method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing method and its device that can superimpose attached information with visually less sense of incongruity on image information while storing a gray level of the image information. SOLUTION: A color conversion section 202 converts a received RGB image signal into a CMYK signal, a various correction processing section 203 corrects the CMYK signal, a pseudo gradation processing section 204 quantizes a noticing pixel of the image signal, an attached information superimposing section 205 superimposes the attached information onto the image information by reading a dot pattern generated by an attached information generating section 207 and the attached position information while storing the gray level in an area to which the attached information is attached depending on the existence of the pixels adjacent to the attached position of the attached information and a printer engine 206 outputs an output image where various information is superimposed on the image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image processing method and apparatus for superposing and outputting additional information different from image information on image information.

[0002]

2. Description of the Related Art In recent years, color image recording apparatuses such as printers and copiers have made great progress in terms of both performance improvement and widespread use, and full-color image recording apparatuses are also of silver halide type, thermosensitive type, electrophotographic type. Devices using a large number of output methods such as an electrostatic recording method and an ink jet method have been developed, and high-quality images have been obtained and have begun to spread widely. However, this has created new problems.

The problem is that banknotes and securities can be easily forged using a full-color image recording apparatus.
Along with this, it has become necessary to install a function for preventing forgery in the recording apparatus, and various full-color image recording apparatuses in recent years are equipped with various forgery prevention functions. The most common method is to print a regular dot pattern representing the machine number of the recording device on the paper at the time of recording, and the dot pattern hit on the bill when a forged bill is found This is a so-called tracking pattern method in which a machine number is determined from the data and a recording device from which the data is output is specified. In addition, since this dot pattern is printed on all output images, it is general that the dot pattern is printed with yellow having the lowest visibility.

[0004]

However, the above-mentioned prior art has the following problems.

FIG. 1 is a diagram showing a configuration of an image processing apparatus for performing a general additional information embedding process. In the figure, first, an input image signal represented by RGB components is
In step 1, the color components are converted into four color components of C (cyan), M (magenta), Y (yellow), and K (black), and each color component is subjected to a correction process in various correction processing units 102. Next, in the pseudo gradation processing unit 103,
Pseudo gradation processing is performed using a method such as an organized dither method or an error diffusion method.

For the image signal subjected to the above processing,
The additional information generated by the additional information generation unit 105 is superimposed (added) on the Y component, and each component is input to the printer engine 104 to print an image to which some information other than the image information is added. be able to.

However, when a predetermined dot pattern is added by simple addition as in the above-described additional information superimposition processing method, the number of pixels naturally changes around the dot pattern. That is, the fact that the number of pixels changes on the image subjected to the pseudo gradation process means a change in the density, and when such a state occurs, no matter how yellow is a component that is hard to detect visually, Naturally, unnatural dots can be visually confirmed.

In order to avoid such a state, when adding a dot pattern to an image signal on which pseudo gradation processing has been performed, the density (the number of pixels) is preserved in accordance with the situation of the peripheral portion. It is necessary to perform some processing for this.

An invention proposed in view of such a problem is disclosed, for example, in Japanese Patent Laid-Open No. Hei 5-244389, which is a process performed on image information before pseudo gradation processing is performed. There is no description about a method of adding a dot pattern while preserving the density of the image information after the pseudo gradation processing.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an image processing method and apparatus capable of superimposing additional information with little visual discomfort while preserving the density of image information. I do.

[0011]

In order to achieve the above object, the present invention provides an image processing apparatus for superimposing additional information different from image information on image information and outputting the image information. Means, pseudo-gradation processing means for quantizing a target pixel of the image information, generating means for generating additional information having a specific dot pattern, and the presence of peripheral pixels to which the additional information is added, An additional information superimposing means for superimposing the additional information while preserving the density of the peripheral portion to which the additional information is added.

According to another aspect of the present invention, there is provided an image processing method for superimposing additional information different from the image information on the image information and outputting the image information. A pseudo gradation processing step of quantizing a pixel of interest of information, a generation step of generating additional information having a specific dot pattern, and adding the additional information according to the presence of peripheral pixels to which the additional information is added And an additional information superimposing step of superimposing the additional information while preserving the density of the peripheral portion.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

The image processing apparatus according to the present embodiment
It is efficient to mainly incorporate it as printer driver software in a computer that creates image information to be output to a printer engine. For example, it is necessary to incorporate it as hardware and software in a copying machine, facsimile machine, printer body, etc. Is also possible.

Further, image information can be expressed by pseudo gradation processing used in an ink jet printer, a heat melting type transfer printer, a laser printer and the like.

[First Embodiment] FIG. 2 is a block diagram showing an additional information superimposing method of an image processing apparatus according to a first embodiment. First, an outline of the operation will be described with reference to FIG.
Next, details of each unit will be described.

In FIG. 2, reference numeral 201 denotes an input terminal;
A multi-tone RGB image signal is input. The input signal is converted into a CMYK signal by a color conversion unit 202, subjected to various corrections by various correction processing units 203, and then input to a pseudo gradation processing unit 204. This pseudo gradation processing unit 204
In the above, the input image signal is converted into a quantization level smaller than the number of input gradations by performing pseudo gradation processing,
The gradation is expressed in area by the quantization values of a plurality of pixels. In the first embodiment, as a method for performing the pseudo gradation processing, any of the existing systematic dither method, the error diffusion method, and the like may be used.
It is assumed that the quantization value is a binary value of “0” or “1”. Here, it is assumed that dots (ink, toner, and the like) are printed on a recording medium such as paper for a pixel (hereinafter, an on-dot) having a quantization value of “1”.
Note that the CMYK components after pseudo halftone process described above is performed, each _{I c (x, y),} I m (x, y), I
_y (x, y) and I _k (x, y).

Next, the additional information generated by the additional information generation unit 207 shown in FIG. 2 is converted into the additional information superimposition unit 205 by using a predetermined dot pattern.
The Y component I _y (x,
superimposed on y). This makes use of the characteristic that the Y component is more difficult to identify with the human eye than the other components. The information to be added in the additional information superimposing unit 205 may be various information such as a maker name, a model name, a machine number, or an output state when an image is output on paper of the output device. These signals may be necessary. If encrypted, they are superimposed.

After performing the above processing, each of the CMYK components is sent to the printer engine 206, and as a result,
An output image on which various information is superimposed can be obtained.

The above is the outline of the operation of the image processing apparatus according to the first embodiment. Hereinafter, the details of each unit described above will be described. First, the additional information generation unit 207 will be described.

As a general method of superimposing additional information on an image, grid points existing at N pixel intervals in a printable area are defined as shown in FIG. 3, and predetermined grid points are defined on the grid points. The additional information is expressed depending on whether or not there is a dot pattern stored in a storage device in a computer or a printer that performs the processing.

FIG. 4 is a diagram showing an example of a dot pattern according to the first embodiment. In the figure, the places where dots (ink, toner, etc.) are printed on the paper are indicated by black dots. Further, since the origin of the coordinate axis is set at the center of the dot pattern in FIG. 4, for example, the number M of pixels forming the dot pattern as shown in the table in FIG.
And the pixel position _{^{(P x m, P y m}} ) such data would be stored in the storage devices present in the computer or printer to perform the pre-processing.

The additional information generation unit 207 obtains the position to which the above-mentioned dot pattern is added by using means for converting information to be superimposed (such as the printer body number) based on a certain rule. There are various rules for converting to position information. For example, the machine number and model name of the printer body are expressed in a binary series,
Although it is conceivable that each of 1, 0 is represented by the presence or absence of a dot pattern, any method may be used in the first embodiment. Here, the obtained information on the addition position is represented by the grid point interval N and the coordinates (L _x ^z , L _y ^z ) of the Z grid points to be added, as shown in the table of FIG. 5, for example. Are input to the additional information superimposing unit 205. The above is the description of the additional information generation unit 207.

Next, the additional information superimposing process of the additional information superimposing section 205 will be described. FIG. 6 is a flowchart illustrating the additional information superimposing process according to the first embodiment. First, in step S601, the above-described dot pattern data is read, and in subsequent step S602, the additional position information generated by the additional information generation unit 207 is read.

Next, in and after step S603, a dot pattern is added to I _Y (x, y) using these pieces of information. At this time, first, in step S603, it is determined whether or not the pixel originally exists at the position of the pixel to be added.
The determination is made for each of the three points constituting the dot pattern. If the result of the determination is that there is a pixel, it is determined that the number of pixels has not changed in the surrounding area, and the flow advances to step S606 to perform no processing. Then, in step S606, it is determined whether a dot pattern of M pixels has been added.
3, the above-described processing is repeated, and when the processing has been added to all the Z positions, the processing ends in step S608.

If no pixel exists at the position to be added, the flow advances to step S604 to determine whether a pixel exists at a position adjacent to the position to be newly added. Here, if a pixel exists, step S
Proceeding to step 605, in order to save the number of pixels, a process of not printing one of the pixels existing in the peripheral portion (hereinafter referred to as
Off dot).

On the other hand, in step S604, when there is no pixel adjacent to the position to be added, and when the off-dot processing is completed in step S605, the process proceeds to step S607 to newly add a pixel constituting the dot pattern.

FIG. 7 is a diagram showing an example of an image before and after adding a dot pattern according to the first embodiment. (A) shown in the figure is an image before adding a dot pattern, and a gray area is an area to which a dot pattern is added. 6B shows an image to which a dot pattern has been added, and asterisks indicate pixels which originally existed but have been turned off-dot by the processing in step S605 shown in FIG.

According to the first embodiment described above, in a process of superimposing additional information by embedding a dot pattern on an image on which pseudo gradation processing has been performed so as to be invisible, the operation is relatively simple. By this means, it is possible to maintain the number of pixels (density) at the same level before and after the information addition processing, and it is possible to superimpose additional information without a sense of discomfort visually.

[Second Embodiment] Next, a second embodiment according to the present invention will be described in detail with reference to the drawings.

In the first embodiment described above, the case where the quantization value is binary (0 or 1) is assumed as the output result of the pseudo gradation processing unit 204 shown in FIG. In the embodiment, a case of three values (0, 1, 2) is assumed.

FIG. 8 is a diagram showing an image after the pseudo gradation process according to the second embodiment is performed. In the figure, pixels indicated by density level 2 and density level 1 indicate pixels (on dots) on which dots are printed on paper using ink, toner, or the like, and are indicated by density level 0. Pixels indicated are pixels on which nothing is printed (off-dotted). Further, it means that a pixel represented by density level 2 is printed at twice the density of a pixel represented by density level 1. Second
In the embodiment of the present invention, when performing a process of adding a predetermined dot pattern to a pseudo gradation image quantized to a multi-valued level (two or more values), in the added peripheral portion, Processing is performed so that the sum of the quantized values does not change.

FIG. 9 is a flowchart showing the additional information superimposing process according to the second embodiment. First, step S
In step 901, a dot pattern that is predetermined and stored in a storage unit of a computer or a printer that performs processing in the second embodiment is read in the same manner as in the first embodiment.

FIG. 10 is a diagram showing a dot pattern used in the second embodiment. In the second embodiment, it is assumed that this dot pattern is described by, for example, data as shown in a table in FIG. 10 and is stored in a storage device. In the drawing, the difference from the first embodiment is that a density level when a dot pattern is added is described.

Next, in step S902 shown in FIG. 9, the position information added a dot pattern _{^{(L x z, L y z}} )
Read. This processing is the same as that described in the first embodiment.

Next, in step S903, an increase ΔD in density due to the addition of the above-mentioned dot pattern to the Z-th grid point position (L _x ^z , L _y ^z ) is calculated using the following equation. . Here, k = 1,..., M.

The _{ΔD = M · V-ΣI y} (N · L x z + P x k, N · L y z + P y k) (2.1) The above equation, the sum of the concentration levels of the pixels constituting the dot pattern This means that an increase in density is calculated by taking the difference from the sum of pixels originally existing at the position of the pixel to be added.

Next, pixels of an amount corresponding to the density increase ΔD obtained by the above equation (2.1) are converted into the image I _y (x,
Off-dotting is performed from y). Here, the off-dot processing is performed. First, in step S904,
As shown in FIG. 11, to set the density storage area locations ^{_{(N · L x z, N}} · L y z) S pixel square blocks around the to add a dot pattern described above, from its central position, the Distance T to pixel I _y (x ′, y ′) existing in the area
(x ′, y ′) is calculated using the following equation.

T (x ′, y ′) = {(x′−N _× L _x ^z ) ² + (y′−N _× L _y ^z ) ² } (2.2) Using this result, in step S 905, , Distance T (x ',
Off-dot processing is performed in order from the pixel with the smallest y '). At this time, the off-dotted pixel value is subtracted from the density increase ΔD by the following equation.

The _{ΔD = ΔD-I y (N} · L x z + R x k, N · L y z + R y k) (2.3) Next, in step S906, the dot-off process until the [Delta] D <0 repeat. When the off-dot processing is completed, the process advances to step S907 to add pixels forming the dot pattern to the image I _y (x, y). Then, in step S908, the processing from step S903 is repeated until the embedding in all positions is completed.

FIG. 12 is a diagram showing an example of an image before and after off-dot conversion processing in the second embodiment. An asterisk in FIG. 7A indicates a pixel that is to be turned off dot as a result of performing the off dot processing according to the second embodiment. When attention is paid to the areas A and B in (a) shown in the figure, since the pixel value does not originally exist at the position where the pixel forming the dot pattern is added, the equation (2.
1) is as follows.

ΔD = 3 · 2−0 = 6 (2.4) From this result, the pixels corresponding to the density level 6 in both regions are turned off in the order in which the pixels are located closer to the center where the dot pattern is added. It will become dots. That is, for the area A, three pixels of density level 2
In region B, six pixels of density level 1 are turned off-dot, and the obtained image is as shown in FIG. 12B.

According to the second embodiment described above, it is possible to store the sum of the density levels in the peripheral portion to which the dot pattern has been added, and it is possible to superimpose additional information with little visual discomfort. .

Third Embodiment Next, a third embodiment according to the present invention will be described in detail with reference to the drawings.

In the third embodiment, as in the second embodiment, it is assumed that the quantized output value of the pseudo gradation processing unit 204 is ternary (0, 1, 2).

FIG. 13 is a diagram showing an image after the pseudo gradation processing in the third embodiment has been performed. In the drawing, pixels indicated by density level 2 and density level 1 are pixels on which dots are printed at high density and medium density, respectively, using ink or toner on paper (on-dot).
And the pixel indicated by the density level 0 indicates a pixel on which nothing is printed (off-dotted).

Also in the third embodiment, the pseudo gradation image quantized to the multi-valued level (two or more values) is
When performing a process of adding a predetermined dot pattern, a process is performed so that the sum of the quantization values does not change in the added peripheral portion.

FIG. 14 is a flowchart showing the additional information superimposing process according to the third embodiment. First, in step S1401, a dot pattern that is predetermined and stored in a storage device of a computer or a printer that performs the processing of the third embodiment is read in the same manner as in the above-described embodiment.

FIG. 15 is a diagram showing a dot pattern used in the third embodiment. In the third embodiment, this dot pattern is described by data as shown in FIG. 16, for example, and is stored in the storage device. It should be noted that, in the figure, similarly to the second embodiment, the density levels of the pixels constituting the dot pattern are described.

Next, in step S1402 shown in FIG. 14, position information (L _x ^z , L _x
y ^z ). This processing is the same as that described in the above embodiment. Also, the calculation process of the density increase ΔD in step S1403 uses the equation (2.1) as described in the second embodiment.

Next, in step S1405, pixels of an amount corresponding to the density increase ΔD obtained by the equation (2.1) are off-dotted from the image I _y (x, y). In this off-dot conversion process, as shown in FIG. 17, the order in which pixels are turned off-dot is determined in advance, and the off-dot conversion order data is described, for example, as shown in FIG. It is stored in a computer to be executed or a storage device built in the printer main body. Then, when the pixels are turned off-dot in the order shown in FIG. 17, the off-dotted pixel values are subtracted from the density increase ΔD by the following equation.

[0052] _{ΔD = ΔD-I y (N} · L x z + R x k, N · L y z + R y k) (3.2) Next, in step S1406, until [Delta] D <0, the dot-off process repeat. When the off-dot processing is completed, the process proceeds to step S1407,
Pixels constituting the dot pattern are represented by an image I _y (x, y)
Add on top. Then, in step S1408,
Step S1 described above until the embedding in all positions is completed.
The processing after 403 is repeated.

FIG. 19 is a diagram showing an example of an image before and after off-dot conversion processing in the third embodiment.

According to the third embodiment described above, it is possible to store the sum of the density levels in the peripheral portion to which the dot pattern is added, and it is possible to superimpose additional information with little visual discomfort. .

Even if 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, a facsimile). Device).

An object of the present invention is to supply a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and to provide a computer (CPU or MP) of the system or apparatus.
It goes without saying that U) can also be achieved by 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.

As a storage medium for supplying the program code, for example, a floppy (registered trademark) disk,
Hard disk, optical disk, magneto-optical disk, CD-
A ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, and the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) running on the computer based on the instruction of the program code. ) May perform some or all of the actual processing, and the processing may realize the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instruction of the program code, It goes without saying that the CPU included in the function expansion board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

[0061]

As described above, according to the present invention, when additional information having a specific dot pattern is added to an image subjected to pseudo gradation processing, pixels existing in the added peripheral portion are turned off. Dot formation makes it possible to preserve the density state, and it is possible to superimpose additional information with little visual discomfort.

Further, by adjusting the density of the image information in the peripheral portion to which the additional information is added in accordance with the density of the additional information to be added, it is possible to add information with less visual discomfort.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an image processing apparatus that performs a general additional information embedding process.

FIG. 2 is a block diagram illustrating an additional information superimposing method of the image processing apparatus according to the first embodiment.

FIG. 3 is a diagram illustrating an example of an image to which a dot pattern has been added.

FIG. 4 is a diagram illustrating an example of a dot pattern according to the first embodiment.

FIG. 5 is a diagram illustrating an example of generated additional position information.

FIG. 6 is a flowchart illustrating additional information superimposition processing according to the first embodiment.

FIG. 7 is a diagram illustrating an example of an image before and after adding a dot pattern according to the first embodiment.

FIG. 8 is a diagram illustrating an image after pseudo tone processing according to a second embodiment.

FIG. 9 is a flowchart illustrating additional information superimposition processing according to the second embodiment.

FIG. 10 is a diagram showing a dot pattern used in the second embodiment.

FIG. 11 is a diagram illustrating an example of a density storage area according to the second embodiment.

FIG. 12 is a diagram illustrating an example of an image before and after off-dot conversion processing according to a second embodiment.

FIG. 13 is a diagram illustrating an image after pseudo gradation processing according to the third embodiment is performed.

FIG. 14 is a flowchart illustrating additional information superimposition processing according to the third embodiment.

FIG. 15 is a diagram showing a dot pattern used in the third embodiment.

FIG. 16 is a diagram illustrating an example of creating a database of dot patterns according to the third embodiment.

FIG. 17 is a diagram illustrating an example of an off-dot conversion order according to the third embodiment.

FIG. 18 is a diagram showing the creation of a database of off-dot order in the third embodiment.

FIG. 19 is a diagram illustrating an example of an image before and after off-dot conversion processing according to a third embodiment.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Nobutaka Miyake 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term within Canon Inc. (reference) 2C061 AQ04 AQ05 AQ06 AR01 HH00 HN15 2H034 FA01 5B057 AA20 CA01 CA08 CA12 CA16 CB01 CB07 CB12 CB16 CE08 CE13 CE18 DA20 DB02 DB06 DB09 5C076 AA14 AA27 BA06

Claims (16)

[Claims] An image processing apparatus for superimposing additional information different from the image information on the image information and outputting the image information, an input means for inputting the image information, and a pseudo gradation for quantizing a pixel of interest of the image information Processing means; generating means for generating additional information having a specific dot pattern; and, in accordance with the presence of a peripheral pixel to which the additional information is added, storing the density of the peripheral part to which the additional information is added while storing the additional information. And an additional information superimposing means for superimposing the information. 2. The image processing apparatus according to claim 1, wherein the generation unit calculates position information for adding the specific dot pattern. 3. The additional information superimposing means includes: first reading means for reading the specific dot pattern; second reading means for reading additional position information generated by the generating means; When adding to the image information, a determination unit that determines whether it is necessary to add a pixel that did not exist on the image information newly, and when the determination unit determines that a new pixel has been added, 2. The image processing apparatus according to claim 1, further comprising: off-dot conversion means for off-dotting a peripheral pixel of the pixel. 4. The additional information superimposing means includes: first reading means for reading the fixed dot pattern; second reading means for reading additional position information generated by the generating means; When adding a pattern to image information,
Increasing density calculating means for calculating the density increased by the addition; and off-dot converting means for off-dotting a pixel corresponding to the value obtained by the increasing density calculating means from among the pixels present in the area. 2. The method according to claim 1, wherein
An image processing apparatus according to claim 1. 5. The off-dotting means, comprising: a distance measuring means for measuring a distance to each pixel present in the area; and a distance obtained by the distance measuring means, in ascending order of distance.
The image processing apparatus according to claim 4, further comprising an off-dot conversion unit configured to perform off-dot conversion on pixels having a density corresponding to the value obtained by the increase density calculation unit. 6. The off-dot conversion means, wherein the order in which pixels are deleted is determined in advance, and the off-dot conversion order is determined according to the off-dot conversion order determined by the off-dot conversion order determination means. 5. The image processing apparatus according to claim 4, further comprising an off-dot conversion unit configured to perform off-dot conversion on pixels having a density corresponding to the value obtained by the increase density calculation unit. 7. An image processing method for superimposing additional information different from the image information on the image information and outputting the image information, comprising: an inputting step of inputting the image information; and a pseudo gradation for quantizing a pixel of interest of the image information. A processing step; a generating step of generating additional information having a specific dot pattern; and, in accordance with the presence of a peripheral pixel to which the additional information is added, storing the density of a peripheral portion to which the additional information is added while storing the additional information. And an additional information superimposing step of superimposing the information. 8. The image processing method according to claim 7, wherein the generating step calculates position information to add the specific dot pattern. 9. The additional information superimposing step includes a first reading step of reading the specific dot pattern, and a second reading step of reading the additional position information generated in the generating step.
A reading step of determining whether or not it is necessary to newly add a pixel that did not exist on the image information when adding the specific dot pattern to the image information; and 8. An image processing method according to claim 7, further comprising the step of: when it is determined that a pixel has been added to the pixel, off-dot-converting a pixel around the pixel. 10. The additional information superimposing step includes: a first reading step of reading the fixed dot pattern; a second reading step of reading the additional information generated in the generating step; When adding to the image information, an increased density calculating step of calculating an increased density due to the addition, a pixel corresponding to the value obtained in the increased density calculating step is selected from the pixels existing in the area. The image processing method according to claim 7, further comprising an off-dotting step of off-dotting. 11. The off-dot forming step includes: a distance measuring step of measuring a distance to each pixel existing in the area; and a distance obtained in the distance measuring step, in order from a shorter distance.
The image processing method according to claim 10, further comprising: off-dotting a pixel having a density corresponding to the value obtained in the increase density calculating step. 12. The off-dot conversion step, wherein the order in which pixels are deleted is determined in advance, and the off-dot conversion order is determined according to the off-dot conversion order determined in the off-dot conversion order determination step. 11. The image processing method according to claim 10, further comprising an off-dot conversion step of off-dot converting a pixel having a density corresponding to the value obtained in the increase density calculation step. 13. A computer-readable storage medium storing a program code of an image processing method for superimposing additional information different from the image information on the image information and outputting the superimposed information, wherein a code of an input step of inputting the image information is provided. A code of a pseudo-gradation processing step for quantizing a target pixel of the image information, a code of a generation step of generating additional information having a specific dot pattern, and the presence of peripheral pixels to which the additional information is added. A code for an additional information superimposing step of superimposing the additional information while preserving the density of a peripheral portion to which the additional information is added. 14. An input unit for inputting image information, a holding unit for holding predetermined additional information, an addition unit for adding the predetermined additional information to the image information on a pixel-by-pixel basis, An image processing apparatus comprising: an adjusting unit that adjusts the density of image information in a peripheral portion to be added according to the density of the additional information. 15. An inputting step of inputting image information; a holding step of holding predetermined additional information; an adding step of adding the predetermined additional information to the image information in a pixel unit; Adjusting the density of the image information in the peripheral portion to be added in accordance with the density of the additional information. 16. A computer readable storage medium storing a program code of an image processing method, wherein: a code of an input step of inputting image information; a code of a holding step of holding predetermined additional information; A code of an addition step of adding the predetermined additional information in pixel units, and a code of an adjustment step of adjusting the density of image information in a peripheral portion to which the additional information is added, according to the density of the additional information. A storage medium characterized by having: