JPH1127530A - Image processing apparatus and method, and storage medium - Google Patents

Abstract

(57) [Problem] To identify a specific pattern added to image data after dither processing when a density pattern of a matrix of image data subjected to dither processing is similar to a specific pattern added to the image data. Can not do. SOLUTION: Non-linear output characteristics of input image data are corrected in a first γ table 1 and a comparison processing unit 2
Then, the output result of the first γ table 1 is compared with the threshold value stored in the threshold value memory 3, and the pixel modulation intensity is obtained by the second γ table 4. The adder 5 adds the result of the second γ table and the specific pattern stored in the specific pattern generation unit 6 and prints the result on a medium such as recording paper via the pixel modulation unit 7 and the printing unit 8. Do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and method, and a storage medium, for example, for adding, as a specific pattern, a device number or the like of an apparatus that has output an image to dithered image data. The present invention relates to an image processing apparatus and method, and a storage medium storing the method.

[0002]

2. Description of the Related Art Pseudo halftone processing known as dither processing is one of halftone processing techniques for dealing with natural images such as photographs. First, the principle operation will be described with reference to FIG.

For example, in order to express a halftone with pixels that can express either white or black, some pixels are combined into one block, and density processing is performed for each block. That is, the number of black pixels is changed for each block so that halftone shading is obtained.

For example, when the gradation density is expressed by 4 × 4 pixels as shown in FIG. 1, the threshold values corresponding to each pixel in the block are set to different values as shown in FIG. As shown in FIG. 1A, the input image data is compared with the value corresponding to each pixel. Next, a pixel whose density level is higher than the threshold value is a black pixel, and a pixel whose density level is lower than the threshold value is a white pixel. Dither processing is a process in which halftones of an output image are simulated by arranging the threshold values differently in this way.

On the other hand, with the improvement of image quality and color of image processing apparatuses such as printers and copiers, there is a social problem that specific documents such as banknotes and securities that should not be copied are copied and used. There is fear.

In order to prevent this problem, Japanese Patent Laid-Open No.
As shown in U.S. Pat. No. 94682, a technique has been proposed in which a specific pattern representing a device number or the like is added to an output image of an image processing device to specify the image processing device that has output the image.

FIG. 2 shows a configuration example of an apparatus for adding a specific pattern.

The R, G, and B input signals are input to an image data processing unit 201, where they are converted into image data representing signal levels of Y, M, C, and K components. The adder 5 adds the image data output from the image data processing unit 201 and a predetermined specific pattern stored in the specific pattern generator 6 in advance, and outputs an image via the image modulation unit 7 and the printing unit 8. .

[0009]

However, the above technique has the following problems. When the density pattern of the matrix of the image data subjected to the dither processing is similar to the specific pattern added to the image data, it is difficult to identify the specific pattern added to the image data after the dither processing.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem. By setting a specific pattern having a matrix size corresponding to the density pattern of image data after dither processing, the specific pattern added to the image data after dither processing is specified. It is an object of the present invention to provide an image processing apparatus and method and a storage medium that facilitate pattern identification.

[0011]

The present invention has the following configuration as one means for achieving the above object.

[0012] An image processing apparatus according to the present invention comprises a reading means for reading a specific pattern of a matrix size set according to a density pattern of input image data from a storage means, and a read specific pattern for the input image data. And an adding means for adding.

Further, processing means for performing dither processing on the input image data based on the threshold value read from the first storage means, and a specific pattern having a matrix size set according to the density pattern of the dither-processed image data, It is characterized by comprising reading means for reading from the second storage means, and means for adding the read specific pattern to the dither-processed image data.

According to the image processing method of the present invention, a specific pattern of a matrix size set according to a density pattern of input image data is read from a storage means, and the read specific pattern is added to the input image data. It is characterized by.

The input image data is subjected to dither processing based on the threshold value read from the first storage means, and a specific pattern having a matrix size set in accordance with the density pattern of the dither-processed image data is stored in a second pattern. It is characterized in that the specific pattern read from the storage means is added to the dither-processed image data.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a description will be given of a moiré manuscript and a method of removing it. In the case of a method in which toners are overlapped by a color image processing device or the like, depending on how the respective colors of Y, M, C, and K overlap, subtractive color mixing occurs when image dots completely overlap, and additive color mixing occurs when image dots are shifted. Become. Further, in the image processing process, a different screen angle is provided for each color in order to remove the moiré manuscript of the color. When the same screen angle is given to each color, a slight angle variation causes a moiré draft (beat). By setting a different screen angle for each color in advance, the moiré frequency becomes higher, Easily remove low frequency moiré manuscripts.

FIG. 3 is a conceptual diagram showing a basic halftone dot.

A halftone dot having a screen angle is formed by arranging the basic halftone dots composed of a × a pixels with appropriate displacement. The portion of the gap C generated at this time may be appropriately attached to a cell corresponding to some halftone dot.

Here, displacement vector (deviation of basic halftone dot)
Is u = (a, b), the screen angle θ is θ = a
It is determined from rctan (a / b). Using the values (a, b) of the components of the displacement vector u, the square threshold matrix size corresponding to one cycle of the basic halftone dot is N = LCM
(A, b) × (b / a + a / b). However, LC
M (a, b) represents the least common multiple of a and b.

FIG. 4 shows basic dot sizes 2 × 2 to 5 ×.
Square threshold matrix size N up to 5, screen angle θ, displacement vector u, number of pixels included in basic halftone dot No
= A × a + b × b.

FIG. 5 is a conceptual diagram showing a square threshold matrix.

When a = 3 and b = 1, the square threshold matrix size (N) corresponding to one cycle of a halftone dot is N = 10, as shown in FIG. 4, and the number of pixels contained in the cell is No.
= 10. That is, a threshold (pixel numbers are added in FIG. 4) may be generated for 10 pixels in the X direction.

As described above, the moiré manuscript can be eliminated by giving the screen dots to the basic halftone dots of each color.

Hereinafter, an image processing apparatus and an image processing method according to an embodiment of the present invention will be described in detail with reference to the drawings.

[Basic Configuration] FIG. 6 shows an example of the configuration of an image processing apparatus having a laser beam printer as a printer engine as an embodiment according to the present invention.

The first γ table 1 is a γ table used for correcting non-linear output characteristics of the image output device. The first γ table 1 is configured by a ROM, and stores a default γ table. The comparison processing unit 2 compares the output result of the first γ table 1 with a threshold and outputs the result. The threshold memory 3 stores a predetermined threshold used for comparison with each pixel value of the input image data in a matrix format.

The second γ table 4 is a γ table for obtaining an actual pixel modulation intensity from the comparison result obtained by the comparison processing section 2. The adder 5 adds the processing result of the second γ table and the specific pattern stored in the specific pattern generator 6. The specific pattern generator 6 is a memory that stores a specific pattern. The pixel modulation unit 7
The printing unit 8 performs printing on a medium such as a recording sheet, for performing modulation of pixels. The counter control unit 9 includes the threshold memory 3
Is a control circuit of counters (H counter 101a and V counter 102a, respectively) that count the number of pixels in the horizontal direction and the number of pixels in the vertical direction to control the number of pixels.

The operation of the counter control unit 9 will be described as follows. First, in the initial state, the H counter 101a
And the counter value (H, V) of the V counter 102a is initialized to (H, V) = (0, 0). Assuming that the size of the threshold matrix is M × N (where M is the number of pixels in the horizontal direction and N is the number of lines in the vertical direction), and if the number of gradation representations of one pixel is P, the threshold memory 3 P types of thresholds corresponding to the address (0, 0) are loaded into the comparison processing unit 2. In the comparison processing unit 2, P comparators are placed in parallel.
Thresholds are input.

Next, the input image data is stored in the first γ table 1
Are sent to the comparison processing unit 2 after the γ conversion. In the comparison processing unit 2, the comparison between the γ-converted value and the threshold value provided from the threshold value memory 3 is performed in parallel by P comparators.
Here, when the value obtained by the γ conversion is larger than the threshold, “Tru
Assuming that the comparator is set to output “e”, the comparison processing unit 2 counts the number of “True” output and converts the number from 0 to (P−1). The numerical value output from the comparison processing unit 2 is input to the second γ table 4, converted into an n-bit pixel modulation intensity signal for one pixel, and sent to the adder 5.

The counter control unit 9 operates as an H counter 101a.
The timing for controlling the V counter 102a will be described with reference to FIG.

The horizontal synchronizing signal (Lsync) is a line synchronizing signal which is generated at every one scanning break in image formation. The vertical synchronization signal (TOP) is a signal generated each time image formation for each of the Y, M, C, and K components is completed. The H counter 101a outputs a horizontal synchronization signal (Ls
Upon receipt of (ync), the internal H counter 101a is reset to 0. Thereafter, the H counter 101a counts the image clock signal (CLK). However, the H counter 101a is a cyclic counter having a cycle M that becomes 0 again after counting M pixels.

When receiving the vertical synchronizing signal (TOP), the V counter 102a resets the internal V counter 102a to 0.
Reset to. However, the V counter 102a is a cyclic counter having a cycle N that becomes 0 again after counting N lines. Therefore, the output (H, V) of the counter represents the local coordinates of the pixel of interest in the threshold matrix. When the image processing for one page is completed, image data is output from the printing unit 8.

In the counter control unit 10, the address of the specific pattern stored in the specific pattern generation unit 6 in advance is controlled by the H counter 101b and the V counter 102b in the counter control unit 10, and M × N (where M is The number of pixels in the horizontal direction, and N is the number of lines in the vertical direction.)

The details are as follows. H counter 101
b shows an image clock signal (C) which is a reference signal in the main scanning direction.
LK) is input. When receiving the horizontal synchronization signal (Lsync), the H counter 101b resets the internal H counter 101b to zero.

Video encoder signal (VideoEN)
Is a signal that becomes Lo only during a section where image data is input, and enables the H counter 101b to operate during that section.
H counter 10 in synchronization with the image clock signal (CLK)
1b counts up. Next, the density HV converter 11
, A predetermined count value (M count in this case) is detected in accordance with the information from the H.sub.1, and a cyclic counter for resetting the H counter 101b to 0 is formed.

The V counter 102b is reset by a TOP signal, which is a reference signal in the sub-scanning direction, and forms a cyclic counter using the horizontal synchronizing signal (LSync) as a reference clock (CLK) similarly to the H counter 101b. Value (in this case, N count) is detected and the V counter 1
02b is reset to 0.

The specific pattern formed by the above operation is repeatedly added to the entire image at regular intervals. The addition of the specific pattern and the input image data by the adder 5 averages the density by area gradation so that the original color of the input image data does not change.

FIG. 8 is a diagram for explaining an operation for setting a matrix size to which a specific pattern is added based on the matrix density after dither processing.

FIG. 8A shows an example of the matrix density after dither processing. FIG. 8B shows an example in which a matrix size to which a specific pattern is added is set based on the matrix density after dither processing. For example, when the matrix density after dither processing corresponds to 00H, the size of the matrix to which the specific pattern is added is 4 × 4, and when the matrix density corresponds to 01H, the matrix size is 5 × 5 and the density is 02H. , The size of the matrix is set to 6 × 6.

As described above, the matrix size to which a specific pattern is added is set based on the matrix density after dither processing. The size may be smaller than the matrix size after dither processing, and may be larger. It is possible and even equal.

FIGS. 9 and 10 illustrate a process of adding a matrix to which a specific pattern having a different size is added to the matrix after the dither processing.

Assume that the relationship between the matrix density after dither processing and the matrix size to which a specific pattern is added is as shown in FIG.

For example, when the matrix density (the number of black pixels) after the dither processing is 0, the matrix size to which the specific pattern is added is 2 × 2, and similarly, the matrix density (the number of black pixels) after the dither processing is 2 In the case of, the matrix size to which the specific pattern is added is 4 × 4, and when the matrix density (the number of black pixels) after dither processing is 10, the matrix size to which the specific pattern is added is 12 × 12. The matrix after the addition is as shown in FIG.

The specific pattern is stored in advance in the specific pattern generating section 6 of FIG. 6 and utilizes the fact that the human eye has a low discriminating ability with respect to the density component of Y (yellow). It is added when an image is formed.

FIG. 11 is a diagram for explaining the averaging of the matrix density of a specific pattern.

FIG. 11A shows a pixel area (M pixels) × (N lines) of a matrix of a specific pattern. FIG.
In 1 (B), the pixel area M1 is modulated so that the pixel density becomes positive, and the pixel area M2 is modulated so that the pixel density becomes negative. Then, the matrix density of the specific pattern is averaged. FIG.
(C) shows that the specific pattern subjected to the image processing is repeated at a predetermined cycle (L) and added to the image data. The image data including the specific pattern is output via the pixel modulation unit 7 and the printing unit 8.

In the embodiment described above, an image processing apparatus provided with a laser beam printer is taken as an example. However, the present invention is not limited to this, and other pseudo intermediate processing such as a copying apparatus and a facsimile is applied. It goes without saying that the present invention can be applied to an image processing apparatus.

Further, it is needless to say that the present invention can be applied to a case where the matrix after dithering the input image data is represented by multi-values.

[0049]

[Other Embodiments] 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 (for example, a copying machine) Machine, facsimile machine, etc.).

Another object of the present invention is to provide a system or an apparatus with a storage medium storing software program codes for realizing the functions of the above-described embodiments,
And MPU) read and execute 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 disk, a hard disk, an optical disk, a magneto-optical disk,
A D-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or 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 card 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 a CPU or the like provided 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.

[0053]

As described above, according to the present invention, by setting a specific pattern having a matrix size corresponding to the density pattern of the image data after dither processing, the specific pattern added to the image data after dither processing can be obtained. An image processing apparatus and method and a storage medium that facilitate the identification of a document can be provided.

[0054]

[Brief description of the drawings]

FIG. 1 is a diagram for explaining general pseudo halftone processing (dither method);

FIG. 2 is a diagram showing a configuration example of a device for adding a general specific pattern,

FIG. 3 is a diagram for explaining a displacement vector of a basic halftone dot according to one embodiment of the present invention;

FIG. 4 is a diagram showing parameter values when a basic cell size is changed according to an embodiment of the present invention;

FIG. 5 is a diagram for explaining a method of determining the size of a square threshold matrix size and the number of pixels included therein according to an embodiment of the present invention;

FIG. 6 is a diagram illustrating a configuration example of an image processing apparatus according to an embodiment of the present invention;

FIG. 7 is a timing chart of each signal for controlling an address of an image data matrix according to an embodiment of the present invention;

FIG. 8 is a diagram for explaining a dither pattern and a matrix size after image density conversion according to one embodiment of the present invention;

FIG. 9 is a view for explaining an example of the relationship between the matrix density after dither processing and the matrix size to which a specific pattern is added according to an embodiment of the present invention;

FIG. 10 is a diagram for explaining an addition result of a matrix after dither processing and a matrix size to which a specific pattern is added according to an embodiment of the present invention;

FIG. 11 is a diagram illustrating a process of adding a specific pattern to image data according to an embodiment of the present invention.

Claims (13)

[Claims] 1. A reading unit for reading a specific pattern of a matrix size set according to a density pattern of input image data from a storage unit, and an adding unit for adding the read specific pattern to the input image data. An image processing apparatus characterized by the above-mentioned. 2. The image processing apparatus according to claim 1, further comprising setting means for setting the matrix size according to a density pattern of a dither matrix of the input image data. 3. A processing means for performing dither processing on input image data based on a threshold value read from the first storage means, and a specific pattern having a matrix size set according to a density pattern of the dithered image data. An image processing apparatus comprising: reading means for reading from a second storage means; and means for adding a read specific pattern to the dither-processed image data. 4. The image processing apparatus according to claim 3, further comprising setting means for setting the matrix size according to a density pattern of a dither matrix used for the dither processing. 5. The apparatus according to claim 1, wherein a matrix size set by said setting means is substantially proportional to an image density represented by said density pattern.
An image processing apparatus described in any one of the above. 6. The apparatus according to claim 1, wherein the adding unit repeatedly adds the specific pattern at a predetermined cycle.
The image processing apparatus according to claim 1. 7. The image processing apparatus according to claim 1, wherein the adding unit adds the specific pattern as density data of a yellow component. 8. The image processing apparatus according to claim 1, wherein the specific pattern is a pattern unique to the apparatus. 9. The image forming apparatus according to claim 1, further comprising a forming unit configured to form a visible image on a recording medium based on the image data output from the adding unit. The described image processing device. 10. An image processing method, wherein a specific pattern of a matrix size set according to a density pattern of input image data is read from a storage means, and the read specific pattern is added to the input image data. . 11. A dither process is performed on input image data based on a threshold value read from the first storage means, and a specific pattern of a matrix size set according to a density pattern of the dither-processed image data is converted to a second pattern. An image processing method comprising: reading out from a storage unit; and adding the read-out specific pattern to the dither-processed image data. 12. A storage medium storing a program code for image processing, the program code including a step of reading a specific pattern of a matrix size set according to a density pattern of input image data from a storage unit. And a program code for adding the specified pattern to the input image data. 13. A storage medium storing a program code for image processing, the program code being for dithering input image data based on a threshold value read out from a first storage means; A program code for reading out a specific pattern of a matrix size set according to the density pattern of the image data from the second storage means.