JP2001197297A - Image processor and computer readable storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor which can produce a document like printed on a copy forgery preventing paper by using ordinary paper, can form an inconspicuous watermark image pattern and also can easily change the watermark image pattern and a background image. SOLUTION: A background image stored in a background image memory 3 is converted into the output resolution at a resolution converter 4, screen processes at a gradation corrector 5 so as to secure substantial coincidence between the gradation set before and after the screen processing and screen processes at a screen processor 6 into the number of lines larger than the number of the output lines. A mask image stored in a mask image memory 7 is converted into the output resolution at resolution converter 8 and when inputted to a selector 9. The selector 9 selects the screen processed background image or the background image not screen processed and generates a watermark image embedded background image in accordance with the mask image. Then the watermark image background embedded image is composited with the main image stored in a page buffer 2 at a compositing part 11 and outputted to an output device 13 after the screen processing at an ASG 12 by the number of output lines.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image for outputting a latent image-embedded background image in which a mask image is embedded as a latent image in a background image, or for combining and outputting a main image with the latent image-embedded background image. The present invention relates to a processing device.

[0002]

2. Description of the Related Art Conventionally, special paper called copy forgery prevention paper has been used in order to suppress unauthorized copying of confidential documents. The copy forgery prevention sheet is a sheet on which a special pattern which is hard to be seen by human eyes, but in which warning characters and the like which are hidden when copied by a copying machine emerges is printed in advance. When a document printed on this copy forgery prevention paper is copied by a copier, warning characters such as "copy prohibited" appear prominently on the copy, so that psychological protection against the act of illegally copying is made. This is a deterrent and also makes it possible to distinguish between the original and the copy.

FIG. 22 is an explanatory diagram of an example of a print pattern of copy forgery prevention paper. FIG. 22A shows the whole copy forgery prevention paper. The “COPY” area shown in black in FIG. 22A is a latent image portion that appears when copying is performed by the copying machine, and the hatched area surrounding the “COPY” area is a background portion that disappears when copying is performed by the copying machine. is there. The latent image portion and the background portion are printed using the same single color ink so that the apparent color and density are the same. Although not shown, a fine line drawing pattern generally called a camouflage pattern is generally included. The camouflage pattern has a lower density than the other areas, and disappears when copied by a copying machine. In some cases, a symbol mark of a company, a local government, or the like is printed on a part of the copy forgery prevention paper. Such a mark is indicated by a star-shaped figure in FIG.

FIG. 22B is an enlarged view of a boundary portion between a latent image portion and a background portion (a broken circle portion in FIG. 22A). The latent image portion is configured by relatively sparsely arranging relatively large dots (dots having a low line number). Further, the background portion is configured by arranging relatively small dots (halftone dots having a high number of lines) relatively densely. Generally, the latent image portion has an area ratio of 2
The background portion is made up of halftone dots having an area ratio of about 20% and a line number of about 150 lines.

When a document original printed on the copy forgery prevention paper is copied by a copying machine, the halftone dots constituting the latent image portion have a size and density resolvable by the copying machine. Is done. However, the halftone dots constituting the background portion are not copied because the size cannot be resolved by the copying machine. Therefore, only the latent image pattern is raised and copied together with the document image printed on the copy forgery prevention paper. By utilizing this and embedding a warning character such as "copy prohibited" as a latent image in a copy forgery prevention sheet, a warning character such as "copy prohibited" appears prominently in a copy. As a result, unauthorized copying can be suppressed, and the original and the copy can be distinguished.

When preparing a plurality of copies of a document such as a confidential document for which copying is prohibited by using the above-described copy forgery prevention paper, use a copy forgery prevention paper having a serial number as a latent image and copy the copy. 2. Description of the Related Art Copying or printing confidential documents on anti-counterfeit paper has been performed. In this case, serial numbers are managed for each distribution destination using copy forgery prevention paper containing warning characters that differ depending on the distribution destination. In this way, even if a confidential document is copied illegally, by checking the serial number included in the copy, it is possible to determine from which distribution destination the copy was copied,
The source of the illegal copy can be tracked.

By the way, since such copy forgery prevention paper requires special printing in advance, there is a problem that the cost of the paper itself is higher than the paper used in ordinary copying machines and printers. . Further, when the design of the background pattern, logo, symbol mark, etc. is changed, it is necessary to start over from printing on the paper, and there is a problem that it takes time and costs.

In the case of using a serial number for each distribution destination as described above, it is necessary to prepare in advance a copy forgery prevention sheet containing a different serial number for the number of copies to be created. Then, every time a part of the confidential document is printed, it is necessary to replace the copy forgery prevention paper containing a different serial number in the tray of the printer and print one copy at a time. . In addition, it is necessary to manage copy forgery prevention sheets having different contents, and this management cost is also burdened on the user.

As a conventional technique for solving these problems,
For example, there is an image forming apparatus described in JP-A-4-369170. When a plurality of copies of a confidential document are created, this apparatus generates numeric characters corresponding to the number of copies, and copies the confidential document over the background of the document image. However, when a numeric character is combined with an original image to form an image, there is a problem that the combined numeric character is conspicuous in an output image.

As another conventional technique, there is a digital recording apparatus described in, for example, JP-A-7-231384. This digital recording device, when copying and recording image data read by a CCD, superimposes an image subjected to dither processing in which a warning character portion and a background portion have different specific densities, thereby forming a normal sheet. It is intended to obtain the same effect as in the case of using copy forgery prevention paper. In this technique, the image to be superimposed has a specific common density, and is an image in which dithers having different numbers of lines are applied in a warning character portion and a background portion. .
However, there is a problem that warning characters are easily seen depending on the document images to be superimposed. In particular, when the number of characters is small (that is, the background area is large), the warning character tends to be easily visible. Further, since the tone characteristics when printed on paper differ for each dither, there is also a problem that a difference appears in the density between the warning character portion and the background portion on the paper, and the warning character becomes easy to see. Further, since the background is a pattern having a specific common density and uniform density on the entire surface, there is a problem that the degree of freedom in designing the background pattern is low.

Still another conventional technique is disclosed in
There is a system described in US Pat. This system generates a secure background image pattern that is difficult to be copied even by a color copying machine by electronically generating and overlapping a first color pattern and a second color pattern that are difficult to copy when printing a confidential document. Is what you do. According to this system, it is possible to print a confidential document so that a delicate pattern or color tone is not easily reproduced when copied by a color copying machine. Further, an example is described in which a latent image such as a warning character is inserted so that colors reproduced when copied are slightly different. However, in order to realize this technology, it is necessary to use a special single-passage electronic printer with high registration accuracy using multiple color toners, and a printer using an ordinary xerography engine or an inkjet printer, especially a black and white printer There is also a problem that can not be used.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has the same prohibition of copying a confidential document or the like as when using forgery prevention paper using ordinary paper. A latent image pattern is not noticeable, a pattern serving as a latent image and a background image can be easily changed, and furthermore, an image processing apparatus that can be realized independently of each printer is provided. It is intended to do so.

[0013]

SUMMARY OF THE INVENTION The present invention relates to an image processing apparatus for synthesizing a main image with a latent image-embedded background image in which a mask image is embedded as a latent image in a background image and outputting the synthesized image. Dot processing with a rougher number of lines than the number of lines,
By selecting one of the background image and the background image subjected to the halftone processing in accordance with the mask image, a latent image-embedded background image in which the mask image is embedded as a latent image in the background image is generated. Since the halftone dot processing is performed on the portion of the mask image embedded as a latent image with the number of lines coarser than the number of output lines, the halftone portion is faithfully reproduced when read by a copying machine or the like as described in FIG. The mask image is conspicuous in the copy. Therefore, by recording the latent image-embedded background image on a normal white sheet, it is possible to obtain the same effect as in the case of using the copy forgery prevention sheet. In addition, since the used paper is blank, strict management such as the copy forgery prevention paper is not required, and the management burden on the user can be reduced.

At this time, the apparent density changes due to the halftone processing between the latent image portion where the background image has been subjected to the halftone process and the background portion where the halftone process has not been performed. Is easy to see. Therefore, tone correction is performed so that the tone of the latent image portion subjected to the halftone process and the tone of the background portion not subjected to the halftone process substantially match at the time of output.
Thereby, the pattern of the latent image can be made more difficult to see.

Such gradation correction processing can be performed on a background image on which halftone processing is performed, a background image on which halftone processing is not performed, or both. Further, the background image on the side not subjected to the halftone processing can be binarized by the number of output lines. Further, the first and second background images after gradation correction for the same background image can be created and stored. At this time, the second background image may be subjected to halftone processing. Also the first
The background image may be binarized by the number of output lines. The halftone processing can use, for example, a dither method and the binarization processing can use an error diffusion method.

Of course, the main image may be combined with the latent image-embedded background image created in this way to output a combined image. At the time of synthesis, for example, when the main image is a monochrome image and the background image is a color image composed of three components of YMC, the main image is output as a K component image, and the latent image embedded background image is output as a YMC component image. May be output as the corresponding color component image. Further, when the main image is a black-and-white image or a color image, and the latent image-embedded background image is a monochrome image, if the main image is a black-and-white image, the main image is combined with the latent image-embedded background image, When the main image is a color image, the latent image-embedded background image may be combined with only one of the color components other than the K component among the plurality of color components of the main image.

Further, screen processing may be performed on the latent image-embedded background image or the synthesized image by the number of output lines. The screen processing means is usually provided when outputting an image to a printer or the like, and in the image processing apparatus of the present invention, the processing is such that the halftone dot processing means performs halftone processing to generate a latent image embedded background image. Since only a load is applied, processing can be performed at high speed. Further, it is possible to cope with output devices having various numbers of lines simply by making the screen processing based on the number of output lines in the screen processing means correspond to an output device such as a printer, and to cope with future high image quality. .

Alternatively, the generated latent image-embedded background image may be stored in the storage means, and the latent image-embedded background image designated by the instruction means and the main image may be combined to form a combined image. The screen processing can be configured by analog screen processing or error diffusion processing.

Further, if a first resolution conversion means for converting the resolution of the background image into an output resolution and a second resolution conversion means for converting the resolution of the mask image into the output resolution are provided, the background image and the mask can be obtained. The image data amount can be reduced. Therefore, the storage capacity can be reduced even in a configuration in which storage means for storing each image is provided.

It is not necessary to prepare background images (including the first and second background images) and mask images for one page, but prepare images smaller than one page.
It may be configured to be used repeatedly to fill one page.

[0021]

FIG. 1 is a block diagram showing a first embodiment of an image processing apparatus according to the present invention. In the figure, 1 is an image input unit, 2 is a page buffer, 3 is a background image memory, 4 and 8 are resolution conversion units, 5 is a gradation correction unit, 6 is a halftone processing unit, 7 is a mask image memory, and 9 is a mask image memory. A selection unit, 10 is a color identification unit, 11 is a synthesis unit, 12 is an analog screen generator (abbreviated as ASG), 13 is an output device, 14 is a control panel, and 15 is a control unit.

The image input unit 1 receives an input of a main image to be recorded on the background, a background image, a mask image to be embedded as a latent image in the background image, and the like. The page buffer 2 temporarily stores the input document image data as the main image. The background image memory 3 stores a background image. The mask image memory 7 stores a mask image. Note that the background image and the mask image may be images having a lower resolution than the resolution of the image to be output.

The resolution converter 4 converts the resolution of the background image read from the background image memory 3 into an output resolution. The gradation correction unit 5 reproduces the background image whose resolution has been converted by the resolution conversion unit 4 on a sheet of the background image subjected to the halftone processing by the next halftone processing unit 6 and the original background image. The tone correction process is performed so that the densities become substantially equal. The gradation correction unit 5 can be configured by, for example, an LUT (look-up table), or can perform a conversion process using a predetermined function or the like. The halftone processing unit 6 performs halftone processing on the background image subjected to gradation correction by the gradation correction unit 5 with the number of lines coarser than the number of output lines.

The resolution converter 8 converts a mask image stored in the mask image memory 7 into an output resolution.

The selecting unit 9 determines whether the background image has been subjected to halftone processing by the halftone processing unit 6 and the background image not subjected to halftone processing in accordance with each pixel value of the mask image whose resolution has been converted by the resolution converting unit 8. One of the pixels is selected and output. by this,
The mask image can be embedded as a latent image in the background image. The output image is referred to as a latent image embedded background image.

The color identification section 10 identifies whether the input document image data is a color image or a monochrome image. Synthesizing unit 11
Combines the document image data read from the page buffer 2 and the latent image embedded background image output from the selection unit 9 according to the identification result of the color identification unit 10.

In this example, the ASG 12 is provided as an example of the screen processing means. ASG12 is a synthesizing unit 1
Analog screen processing is performed on the composite image output from 1 using the number of output lines. The processing output of the ASG 12 is output to the output device 13. The output device 13 is equipped with, for example, a xerography engine in the following description,
It is assumed that the printer is a printer that records a composite image subjected to analog screen processing on paper. Of course, the output device 13 may have any configuration.

The control panel 14 receives various instructions for the device. Here, the user can instruct the image input unit 1 to input a background image or a mask image by performing a special operation. The control unit 15 controls each unit to perform an image processing operation. In particular, the image input unit 1 is controlled in accordance with an instruction received on the control panel 14 to control input of document image data, a background image, a mask image, and the like, which are main images. The input of the background image and the mask image should not be made unnecessarily changeable from the viewpoint of forgery prevention, and security management or the like may be performed.

Next, an example of the operation of the image processing apparatus according to the first embodiment of the present invention will be described. Before receiving the document image data, the background image is stored in the background image memory 3 and the mask image is stored in the mask image memory 7 in advance.

FIG. 2 is an explanatory diagram of an example of a background image.
FIG. 2A shows the entire background image. Here, it is assumed that the background image is an arbitrary 8-bit grayscale image (gradation levels 0 to 255). The hatched portion in the drawing is a multi-valued solid background image, and as shown by the arrow in the drawing, is a gradation pattern in which the gradation level changes in the vertical direction. The change in the gradation level is, for example, 16
From about 48 to about 48. Furthermore, a camouflage pattern is drawn on the entire surface with fine lines. FIG. 2B shows a partially enlarged background image shown in FIG. The wavy line missing in white is a camouflage pattern. In the background image shown in FIG. 2A, such a camouflage pattern is arranged on the entire surface. In addition, a symbol mark (illustrated by a star) is drawn below the background image shown in FIG. Such a background image may have a lower resolution than the resolution of the output device 13 such as a printer.

FIG. 3 is an explanatory diagram of an example of a mask image. The mask image is an arbitrary binary image. In the example shown in FIG. 3, a character pattern “COPY” is drawn on the mask image. This character pattern becomes a latent image pattern embedded in the background image data. The mask image may have a lower resolution than the resolution of the output device 13 such as a printer.

Such a background image and a mask image are
By inputting a special command from the control panel 14, the control unit 15 can control the image input unit 1 to enable external input of a background image and a mask image. The background image and the mask image input via the image input unit 1 are stored in the background image memory 3 and the mask image memory 7, respectively. By making it possible to input the background image and the mask image from the outside in this manner, the design can be easily changed.

When document image data as a main image is input to the image input unit 1, the input document image data is stored in the page buffer 2. At the same time, the document image data is also input to the color identification unit 10. The color identification unit 10 identifies whether the input document image data is a black-and-white image or a color image.
1 is output.

When the document image data is stored in the page buffer 2, the generation and synthesis processing of the background pattern is started. In this process, if the output device 13 is a printer, for example, the document image data is stored in the page buffer 2 to start the printer, and the background pattern is generated in synchronization with a synchronization signal input from the printer. And a combining process is performed. The operation of the background pattern generation and synthesis processing differs depending on the identification result by the color identification unit 10.

First, the operation when the identification result by the color identification section 10 is a black and white image is as follows. The background image is read from the background image memory 3. The resolution of the read background image is converted to an output resolution by the resolution converter 4. The resolution-converted background image is output to the gradation correction unit 5 and the selection unit 9.

The tone correcting section 5 performs a tone correcting process on the input background image. The gradation correction process is performed for the purpose of correcting a change in gradation characteristics in the halftone processing unit 6 at the subsequent stage. FIG. 4 is a diagram illustrating an example of the tone correction process. FIG. 4A shows the gradation level of the background image when an image obtained by printing a background image entirely on halftone processing without performing gradation correction, and an image obtained by printing an image subjected to screen processing such as error diffusion processing, for example. It shows the characteristics of the reproduction density on paper. In the figure, a indicates the characteristic of the halftone image, and b indicates the characteristic of the screen image. As can be seen from the figure, even in the background images having the same gradation level, the reproduction densities in the case where the halftone processing is performed and the case where the screen processing is performed are usually different. Therefore, if the latent image embedded background image is generated without performing the gradation correction process,
Since the latent image portion (halftone dot) and the background portion (error diffusion) have different reproduction densities on the paper, the latent image is conspicuous as a result,
Not preferred. Therefore, tone correction is performed before the halftone generation processing using a tone curve whose reproduction density characteristic shown in FIG. 4B matches the error diffusion processing. As a result, as shown in FIG. 4C, the reproduction density characteristics of the halftone image and the screen image can be matched. In this way, as a result, the latent image in the output background image can be made less noticeable.

The background image that has been subjected to the tone correction processing is subjected to halftone processing by the halftone processing unit 6 using a line number that is rougher than the output line number. For example, it can be converted into a halftone image having a gradation level of 0 or 255 and a halftone frequency of 50 lines by systematic dither. The halftone-converted background image is output to the selection unit 9. Note that, instead of fixing the step value of each threshold value of the dither matrix used in the halftone dot generation processing, a matrix of threshold values having different step values according to the gradation characteristics is used. Tone correction may be performed at the same time.

In parallel with the processing for the background image described above,
Processing is performed on the mask image. The mask image is read from the mask image memory 7, and the read mask image is converted into an output resolution by the resolution converter 8. The resolution-converted mask image is input to the selection unit 9 as a selection signal.

When the pixel value of the mask image as the selection signal is, for example, 1 (black pixel), the selection unit 9 selects and outputs the pixel value of the background image subjected to halftone processing, and outputs 0 (white pixel). If so, the pixel value of the background image that has not been subjected to halftone processing is selected. For example, in the examples shown in FIGS. 2 and 3, since a character pattern such as “COPY” is drawn in the mask image, the image output from the selection unit 9 is “CO” of the background image data.
A halftone-processed background image is selected for an area corresponding to a character pattern such as “PY”, and the other portion remains a multi-valued background image that has not been halftone-processed. FIG. 5 is an enlarged view of an example of the latent image-embedded background image output from the selection unit 9. FIG. 5 is an enlarged view of a boundary portion at which the selection between the background image subjected to the halftone processing and the background image not subjected to the halftone processing is switched in the selection unit 9. The shaded portion in the figure is the region of the multi-level background image. The portion indicated by the black dots is the area of the background image subjected to the halftone processing, and the dots by the halftone processing appear as they are. That is, the character pattern in the mask image is embedded in the background image as halftone-processed dots. At this time, since the gradation correction processing is performed by the gradation correction unit 5 on the background image that has been subjected to the halftone processing so as to have the same density as the background image that has not been subjected to the halftone processing, the embedded mask is used. The pattern of the image is embedded as a latent image that cannot be seen on paper. By selecting either the background image on which the halftone processing has been performed or the background image on which the halftone processing has not been performed in accordance with the mask image in this way, the latent image in which the mask image is embedded as a latent image is selected. An image embedded background image is generated.

The synthesizing unit 11 receives the latent image-embedded background image generated as described above and the document image data read from the page buffer 2. Synthesizing unit 11
Compares the pixel values of the input document image data and the latent image embedded background image, and selects the larger one as the output pixel,
Output as a composite image.

The combined image is subjected to screen processing by the ASG 12 at the number of output lines. For example, if the output device 13 is 20
If there is a resolution of 0 line, the synthesized image is 200
Pulse width modulation compared to the analog triangular wave
A line screen of lines is formed and output to the output device 13. If the output device 13 is a printer, the output screen image is printed on paper.

FIG. 6 is an explanatory diagram of an example of the analog screen processing. The waveform shown in FIG.
2 shows a composite image input to the へ. The waveform shown in FIG. 6B is a 200-line analog triangular wave which is a reference wave of ASG12. Further, the waveform shown in FIG.
It is an output waveform of ASG12. If the output device 13 is a printer equipped with a xerography engine, FIG.
The laser diode and the polygon mirror are driven by the output waveform shown in (1), and the image is reproduced on the paper.

FIG. 7 is an enlarged view of an example of an image printed on a sheet. FIG. 7 shows a state where the portion shown in FIG. 5 is printed on a sheet. The vertical lines in the figure are 200-line screen patterns reproduced on paper. The background portion, which is a gradation pattern composed of multi-valued pixels in FIG. 5, becomes a waveform having a width corresponding to the density by the 200-line screen processing as shown in the right half of FIG. Therefore, as shown in FIG. 6, printing is performed as a 200-line pattern on paper. On the other hand, FIG.
The portion embedded as a latent image pattern is a halftone dot of 50 lines, and the density is 0 and 25 as described above.
5 Therefore, as shown in the left half of FIG.
When the zero-line analog screen is applied, halftone dots are screen-processed as solid small areas, and reproduced as dots having a width of two to three pixels in width and length. In this way, an image as shown in FIG. 7 is printed on the paper.

In the printed image, as for the latent image portion subjected to the halftone processing, the gradation correction processing is performed by the gradation correction section 5 so that a gradation change from the surroundings does not occur. This is an image in which the latent image is embedded so as not to be noticeable in the background image.

Next, the operation when the identification result by the color identification section 10 is a color image is as follows. Here, the input color document image data is YMCK
It is assumed that the data is input as data of four colors and is output to the output device 13 in the order of KYMC. Therefore, the image processing apparatus outputs an image for each color component in the KYMC color order.

The synthesizing unit 11 transmits the KYM of the document image data from the page buffer 2 for the image formation of the three colors KYM.
The M component is read out, passed through the synthesizing unit 11 and output to the ASG 12 as it is. At the time of forming the C color image, the C component of the document image data read from the page buffer 2 and the latent image embedded background image are combined and output. The process of generating the latent image-embedded background image is the same as that when the document image data is a monochrome image.

That is, in this example, when outputting a monochrome document image, a light gray latent image embedding background image is synthesized, and when outputting a color document image, a light C latent image embedding is performed. The background image is synthesized and output to the output device 13. Of course, in the case of a black and white document image,
A latent image-embedded background image may be combined with a color such as a color, or in the case of a color document image, a latent image-embedded background image of a color other than C, such as M, may be combined.

The image output as described above is printed on paper by an output device 13 such as a printer.
When a printed document image is copied by a copying machine, the 200-line portion constituting the background portion cannot be resolved by the copying machine and the density level is low, so that the copy is not reproduced. On the other hand, with respect to the latent image pattern portion, the 50-dot halftone dot can be sufficiently reproduced by a copying machine, so that it is copied and reproduced. Therefore, when a document image printed by the output device 13 is copied by a copying machine, a latent image pattern such as "COPY" appears on a copy.

In the configuration shown in FIG. 1, the low-resolution background image and the mask image are stored in the background image memory 3 and the mask image memory 7 in advance. However, in order to further reduce the memory capacity, the image is compressed and stored. It is also possible to configure so that In that case, the mask image is M
It is possible to use lossless compression such as MR or JBIG,
The background image can use irreversible compression such as JPEG. Of course, the compression method is arbitrary.

The background image and the mask image are attached to the document image data and input from the outside, and a latent image-embedded background image is generated from the attached background image and mask image and synthesized and output. It is also possible.

Further, it is also possible to adopt a configuration in which a different mask image is input and a different latent image pattern is embedded for each print of one copy, corresponding to a case where a plurality of copies are printed out. It is. Alternatively, a plurality of mask images are stored in the mask image memory 7 in advance, and the mask image to be selected is changed each time one copy is printed. It may be generated each time. With this configuration, it is possible to enter a different serial number for each copy as a latent image pattern.

FIG. 8 is a block diagram showing a second embodiment of the image processing apparatus according to the present invention. In the figure, the same parts as those in FIG. 21 is an accumulation unit, 22 is an image output order control unit, and 23 is an error diffusion processing unit.

In this example, the latent image-embedded background image generated by the selection unit 9 is output to the storage unit 21. The accumulation unit 21
A plurality of latent image embedded background images output from the selecting unit 9 can be stored.

The image output order control unit 22 corresponds to the synthesizing unit 11 in FIG. 1, and includes the document image data read from the page buffer 2 and the latent image embedded background image selected and read from the storage unit 21. And outputs a composite image.

This example shows an example in which an error diffusion processing section 23 is provided as a screen processing means. The error diffusion processing unit 23 performs an error diffusion process on the composite image output from the image output order control unit 22.

The control panel 14 inputs a background image and a mask image by a special operation.
, And the latent image embedding background image to be used can be indicated. The control unit 15 controls the image input unit 1 and controls the storage unit 21 to select and control a latent image-embedded background image to be used in accordance with an instruction from the user on the control panel 14. The control unit 15
Also controls the color to be output to the image output order control unit 22.

Next, an example of the operation of the image processing apparatus according to the second embodiment of the present invention will be described. In this embodiment, a plurality of latent image embedded background images are stored in the storage unit 21 in advance. The latent image embedding background image is
The data is stored in the storage unit 21 as follows.

First, by inputting a special command from the control panel 14, the control unit 15 controls the image input unit 1, and the background image and the mask image input from the outside to the image input unit 1 are respectively converted to the background image. It is stored in the memory 3 and the mask image memory 7. Here, it is assumed that the background image is an arbitrary YMC three component color image. The background image may have a lower resolution than the output resolution in order to reduce the memory capacity. The mask image is an arbitrary binary image. A character pattern such as "COPY" is drawn in the mask image data. This character pattern becomes the latent image pattern embedded in the latent image embedded background image. The mask image may have a lower resolution than the output resolution in order to reduce the memory capacity.

When the background image and the mask image are stored in the background image memory 3 and the mask image memory 7, respectively, a process of generating a latent image embedded background image is started. The background images are read from the background image memory 3 one by one in the order of YMC. The resolution conversion unit 4 converts the resolution of the background image into an output resolution. The resolution-converted background image is output to the gradation correction unit 5 and the selection unit 9.

The tone correcting section 5 performs a tone correcting process on the input background image. This gradation correction processing is performed for the purpose of correcting a change in gradation characteristics in the halftone processing unit 6 in the subsequent stage. Here, the correction characteristics in the gradation correction unit 5 are switched for each color component, and an optimum gradation correction process is performed for each color component. For example, when the gradation correction unit 5 is configured by an LUT, it can be realized by switching the parameters of the LUT for each color component to be processed.

The background image whose gradation has been corrected is supplied to the halftone processing unit 6.
In the above, the halftone processing is performed with the number of lines rougher than the number of output lines. For example, it can be converted into a halftone image having a gradation level of 0 or 255 and a halftone frequency of 50 lines by systematic dither. The halftone-converted background image is output to the selection unit 9.

In parallel with the above-described processing for the background image,
A mask image is read from the mask image memory 7, converted to an output resolution by a resolution conversion unit 8, and then input to a selection unit 9 as a selection signal. The same image data is used for the mask image regardless of the color component to be processed. That is, the mask image stored in the mask image memory 7 is YMC
Are read out for each of the colors, and are read out three times in total.

If the pixel value of the mask image as the selection signal is, for example, 1 (black pixel), the selection unit 9 selects and outputs the pixel value of the background image subjected to halftone processing, and outputs 0 (white pixel). If so, the pixel value of the background image that has not been subjected to halftone processing is selected and output as a latent image embedded background image. Since a character pattern such as “COPY” is drawn in the mask image, the latent image embedding background image output from the selection unit 9 includes a region corresponding to the character pattern such as “COPY” in the background image. The latent image pattern is formed by being dotted, and the other part is a multi-value gray scale image. The process of generating the latent image-embedded background image is basically the same as that of the first embodiment, and therefore, will be described only as described above. As a specific example, a latent image-embedded background image as enlarged and shown in FIG. 5 is obtained. Such a latent image embedded background image is output to the storage unit 21 and stored.

The above processing is performed for the three planes of Y, M, and C. As a result, one latent image-embedded background image is stored in the storage unit 21 separately for the three planes of Y, M, and C. Will be. The storage unit 21 can store a plurality of latent image embedded background images created in this way.

Next, the output operation of the document image data as the main image will be described. First, a latent image-embedded background image to be synthesized at the time of output is selected from the control panel 14, and the selection result is input to the storage unit 21 through the control unit 15.

Thereafter, the document image data to be output is input to the image input unit 1 and stored in the page buffer 2.
Here, it is assumed that the document image data is input as an 8-bit grayscale image.

When the document image data is stored in the page buffer 2, the output process starts. In this case, if the output device 13 is a printer, the printer is started by storing the document image data in the page buffer 2 and the output process is performed in synchronization with a synchronization signal input from the printer. It can be carried out. The output process is a printing operation of a color image, and image data of four colors of KYMC is printed by the printer.

The image output order control unit 22 receives from the control unit 15 a signal indicating a color component for which an image forming process is currently being performed. If the color component indicated by the signal is a K component, the image output order control unit 22
And outputs the document image data. Control unit 15
Is a YCM component, the image output order control unit 22 stores the latent image embedded background image of the color component corresponding to the color component indicated by the signal from the control unit 15 in the storage unit. 21 and read out. The storage unit 21 is provided with a selection signal of a latent image embedding background image from the control unit 15, and for the selected latent image embedding background image, the color components indicated by the signal from the control unit 15 are arranged in the image output order. It is output from the control unit 22.

The image output from the image output order control section 22 is subjected to error diffusion processing in an error diffusion processing section 23. FIG. 9 is a partially enlarged view showing an example of an image before and after error diffusion processing. FIG. 9A shows a latent image-embedded background image similar to that shown in FIG. 5, in which the boundary between the latent image pattern before the error diffusion processing and the background portion is enlarged. The area formed by dots in the drawing is a latent image pattern portion, and the hatched area is a background portion formed by multi-valued pixel values. White wavy lines are camouflage patterns composed of white pixels.

FIG. 9B shows the result of error diffusion processing of the latent image-embedded background image shown in FIG. 9A. FIG.
The dots constituting the latent image pattern in the latent image-embedded background image shown in (A) are composed of pixels having pixel values 0 and 255, for example. Therefore, even if this area is subjected to the error diffusion processing, the result does not change. The pixel having the pixel value 255 becomes a black (1) pixel even if the error diffusion processing is performed, and the pixel having the pixel value 0 is 0 (even if the error diffusion processing is performed). White) pixels. On the other hand, when the low-density background portion is subjected to error diffusion processing, the background portion shown in FIG.
As shown in FIG. 6, small dots (one pixel) are randomly arranged.

The output image subjected to the error diffusion processing in the error diffusion processing unit 23 is input to the output device 13 and is formed. By the above operation, for example, the output device 13
Is an electrophotographic printer, the image corresponding to the document image data is formed with K color (black) toner, and the latent image embedding background image having the same effect as the copy forgery prevention paper is formed with color toner. Will be formed. For example, if the output device 13 is an inkjet printer,
The image corresponding to the document image data is formed with black ink, and the latent image embedded background image is formed with color ink.

When the paper on which the image is formed is copied as a document by a copying machine, for example, the large dots of the latent image portion shown in FIG. 9B are reproduced by the copying machine, but the isolated dots of the background portion are reproduced. Is not reproduced because it cannot be resolved with a copier,
As a result, a latent image pattern appears on the copy.

Note that in the second embodiment,
For example, a color image may be allowed as the main image, and a single color image may be synthesized as the latent image embedded background image. In this case, for example, the latent image embedding background image stored in the storage unit 21 may be a grayscale black and white image, and the image output order control unit 22 may control which color image is to be combined with the image. Good. Needless to say, the color discriminating unit 10 may be provided as in the first embodiment, and the combining process in the image output order control unit 22 may be switched according to whether the main image is a monochrome image or a color image.

FIG. 10 is a block diagram showing an image processing apparatus according to a third embodiment of the present invention. In the figure, the same parts as those in FIG. 31 is a screen processing unit. In the above-described first and second embodiments, examples have been described in which the gradation correction is performed by the gradation correction unit 5 on the background image input to the halftone processing unit 6. However, the present invention is not limited to this, and the gradation correction unit 5 may perform gradation correction on the background image on which the halftone processing is not performed by the halftone processing unit 6. In the third embodiment, a configuration is shown in which gradation processing is performed on a background image on which halftone processing is not performed.

The tone correcting section 5 has a background image stored in the background image memory 3 and the background image subjected to the halftone processing by the halftone processing section 6 and the density reproduced on the paper are almost equal. The tone correction process is performed so that Then, the background image after the gradation correction is used as one input of the selection unit 9. The gradation correction unit 5 can be configured by, for example, an LUT (look-up table). Of course, in addition to the LUT, the present invention may be realized by another method that can obtain the same effect. For example, a method of performing a conversion process of an input pixel value by a predetermined function may be used.

Further, the screen processing unit 31 includes the synthesizing unit 1
The composite image output from 1 is subjected to screen processing and output. The screen processing unit 31 corresponds to the ASG 12 in the first embodiment shown in FIG. 1 and the error diffusion processing unit 23 in the second embodiment shown in FIG. Any type of digital screen such as a digital screen may be used.

Next, an example of the operation of the image processing apparatus according to the third embodiment of the present invention will be described. First, rasterized document image data to be printed out from the outside, a background image, and a mask image to be embedded in the background image are input to the image input unit 1, and stored in the page buffer 2, the background image memory 3, and the mask image memory 7, respectively. Is stored. Here, the document image data and the background image are multi-valued image data of 8 bits (256 levels) per pixel, and the mask image data is binary image data. The background image and the mask image may be input in advance.

When the input of each image data is completed, the background pattern generation and synthesis processing is started. The background image read from the background image memory 3 is input to the halftone processing unit 6 and the gradation correction unit 5. The halftone processing unit 6 performs a halftone generation process on the input background image with a lower screen ruling than the screen ruling of the output device 13, and outputs the halftone-converted background image to the selecting unit 9. Here, the halftone-converted background image output from the halftone generation unit 6 has a pixel value of a black pixel = 255 and a pixel value of a white pixel, for example, when the gradation level can take a value of 0 to 255. = 0.

The tone correcting section 5 performs a tone correcting process on the input background image and outputs the result to the selecting section 9. By this gradation correction processing, the density of the multi-valued background image subjected to the gradation correction processing input to the selection unit 9 and the background image subjected to the halftone processing are made substantially equal to each other on the paper. ing. For example, the gradation correction processing may be performed on the background image as described with reference to FIG. In this case, processing is performed such that the density of the image of the background portion that has not been subjected to the halftone processing approaches the density of the latent image portion that has been subjected to the halftone processing. This makes the latent image characters embedded in the background of the document less conspicuous on paper printed and output from the output device 13, for example.

In parallel with the above-described processing, a mask image is read from the mask image memory 7 and input to the selection unit 9. According to the value of each pixel of the input mask image, the selection unit 9 selects one of a background image subjected to gradation correction processing by the gradation correction unit 5 and a background image subjected to halftone processing by the halftone processing unit 6. One corresponding pixel is selected and output. For example, when the mask image is a white pixel, the corresponding pixel data of the background image subjected to the gradation correction processing is selected, and when the mask image is the black pixel, the corresponding pixel data of the halftone-processed background image is selected. Can be output. As a result, the image data output from the selection unit 9 becomes a background image (latent image embedded background image) in which only the area corresponding to the black area (latent image) of the mask image is embedded with a halftone dot pattern. This latent image embedded background image is output to the synthesizing unit 11.

The synthesizing unit 11 receives the document image data read from the page buffer 2 in parallel.
The synthesizing unit 11 performs a synthesizing process by comparing the pixel values of the document image data and the latent image embedded background image, and selects the larger one of the pixel values, and outputs the result to the screen processing unit 31. The screen processing unit 31 converts the multi-valued image data input by a screen process such as an error diffusion process into binary image data. Then, the image data subjected to the error diffusion processing according to the pixel values 0 and 1 is printed out on a sheet by the output device 13.

At this time, since the latent image portion (halftone-processed portion) in the latent image-embedded background image has a gradation value of 0 or 255, the screen processing unit 31 performs error diffusion processing or analog screen processing. Even if the process is performed, the halftone dot pattern is reproduced on a sheet by the output device 13 without being destroyed. Background part other than latent image part (multi-valued background image)
Are subjected to error diffusion processing and analog screen processing by the screen processing unit 31, and are reproduced as random isolated dot patterns on paper. Since the latent image portion and the background portion have been processed so that the reproduction densities on the paper are substantially the same by the gradation correction process, the latent image portion is almost inconspicuous.

Although FIG. 10 does not show the resolution converters 4 and 8, the color discriminator 10, the control panel 14, the controller 15 and the like shown in the first embodiment, they are appropriately shown. Can be provided. Also, this third
In the second embodiment, the same modification as in the above-described first and second embodiments can be performed. For example, as in the second embodiment, a plurality of Is stored in the storage unit 21.
It is also possible to configure so as to make a selection by an instruction. Of course, other various modifications are possible.

FIG. 11 is a block diagram showing a fourth embodiment of the image processing apparatus according to the present invention. In the figure, FIG. 1, FIG.
The same reference numerals are given to the same parts as 0, and the description is omitted.
5-1 is a first gradation correction unit, and 5-2 is a second gradation correction unit. In the above-described first and second embodiments, an example is shown in which the gradation correction processing by the gradation correction unit 5 is performed on the background image input to the halftone processing unit 6, and the third embodiment Has described an example in which the gradation correction processing is performed on the background image on which the halftone processing is not performed. In the fourth embodiment, an example is shown in which tone correction processing is performed on both of them.

The first gradation correcting section 5-1 performs a gradation correcting process on the background image stored in the background image memory 3, and outputs the background image after the gradation correction to one input of the selecting section 9. And The second gradation correction unit 5-2 similarly performs gradation processing on the background image stored in the background image memory 3 and sends the background image after gradation correction to the halftone processing unit 6. Output. The first tone correction unit 5-1 and the second tone correction unit 5-2 are not subjected to halftone processing by the halftone processing unit 6 and the background image subjected to halftone processing by the halftone processing unit 6. The gradation correction processing is performed so that the background image and the background image are reproduced with substantially the same density on the paper. Both the first gradation correction unit 5-1 and the second gradation correction unit 5-2 can be configured by, for example, an LUT (look-up table) or can perform conversion processing using a predetermined function or the like. In this embodiment, since two tone correction units perform the tone correction process,
Correction processing according to an arbitrary reproduction curve is possible.

Next, an example of the operation of the image processing apparatus according to the fourth embodiment of the present invention will be described. First, rasterized document image data to be printed out from the outside, a background image, and a mask image to be embedded in the background image are input to the image input unit 1, and stored in the page buffer 2, the background image memory 3, and the mask image memory 7, respectively. Is stored. Here, the document image data and the background image are multi-valued image data of 8 bits (256 levels) per pixel, and the mask image data is binary image data. The background image and the mask image may be input in advance.

When the input of each image data is completed, the process of generating and synthesizing the background pattern is started. The background image read from the background image memory 3 is input to the first gradation correction unit 5-1 and the second gradation correction unit 5-2.
The first gradation correction section 5-1 performs gradation correction processing on the input background image and outputs the result to the selection section 9.

Similarly, in the second gradation correction section 5-2,
It performs gradation correction processing of the input background image and outputs the result to the halftone processing unit 6. The halftone processing unit 6 performs a halftone generation process on the input background image with a lower screen ruling than the screen ruling of the output device 13, and outputs the halftone-converted background image to the selecting unit 9. Here, the halftone-converted background image output from the halftone generation unit 6 has a pixel value of a black pixel = 255 and a pixel value of a white pixel, for example, when the gradation level can take a value of 0 to 255. = 0.

The above-mentioned first and second tone correction processing sections 5-
The corrections 1 and 2 are performed so that the density of the multivalued background image subjected to the gradation correction processing input to the selection unit 9 and the halftone-processed background image are substantially equal on the paper. ing. This makes the latent image characters embedded in the background of the document less conspicuous on paper printed and output from the output device 13, for example.

In parallel with the above processing, a mask image is read from the mask image memory 7 and input to the selection unit 9. The selection unit 9 performs a gradation correction process by the gradation correction unit 5-1 and a background image processed by the dot processing unit 6 in accordance with the value of each pixel of the input mask image. And selects and outputs one of the corresponding pixels. For example,
If the mask image is a white pixel, the gradation correction unit 5-1 selects the corresponding pixel data of the background image subjected to the gradation correction processing, and if the mask image is a black pixel, the halftone processing unit 6 selects the halftone data. The corresponding pixel data of the background image subjected to the point processing can be output. As a result, the image data output from the selection unit 9 becomes a background image (latent image embedded background image) in which only the area corresponding to the black area (latent image) of the mask image is embedded with a halftone dot pattern. This latent image embedded background image is output to the synthesizing unit 11.

The image data read from the page buffer 2 is input to the synthesizing unit 11 in parallel.
The synthesizing unit 11 performs a synthesizing process by comparing the pixel values of the document image data and the latent image embedded background image, and selects the larger one of the pixel values, and outputs the result to the screen processing unit 31. The screen processing unit 31 converts the multi-valued image data input by a screen process such as an error diffusion process into binary image data. Then, the image data subjected to the error diffusion processing according to the pixel values 0 and 1 is printed out on a sheet by the output device 13.

At this time, the latent image portion (halftone-processed portion) in the latent image embedded background image has a gradation value of 0 or 255. Even if the process is performed, the halftone dot pattern is reproduced on a sheet by the output device 13 without being destroyed. The background part (multi-valued background image) other than the latent image part is subjected to screen processing such as error diffusion processing by the screen processing unit 31, and is reproduced on a sheet as a random isolated dot pattern. Since the latent image portion and the background portion have been processed so that the reproduction densities on the paper are substantially the same by the gradation correction process, the latent image portion is almost inconspicuous.

In FIG. 11, the resolution converters 4 and 8, the color discriminator 10, the control panel 14, the controller 15 and the like shown in the first embodiment are not shown. Can be provided. In addition, this fourth
In this embodiment, the same modification as in the above-described second embodiment can be made. Of course, other various modifications are possible.

FIG. 12 is a block diagram showing a fifth embodiment of the image processing apparatus of the present invention. In the figure, the same parts as those in FIGS. 1 and 10 are denoted by the same reference numerals, and description thereof will be omitted. 32 is an error diffusion processing unit. In the above-described first to fourth embodiments, the background portion that is not subjected to the halftone processing is input to the selection unit 9 as a multi-valued image, so that the hardware amount is reduced and the speed is increased. However, for example, even in a configuration in which both the background portion and the latent image portion are input to the selection portion 9 as binary images, the gradation correction process of the latent image portion and the background portion by the gradation correction process is effective. In each of the following embodiments, a configuration example in which a binarization process (an error diffusion process in the following example) is performed on a background image serving as a background portion will be described.

The gradation correcting section 5 performs a halftone processing on the background image stored in the background image memory 3 by the halftone processing section 6 (an image serving as a latent image), The tone correction process is performed so that the background image subjected to the error diffusion process by the processing unit 32 is reproduced with substantially the same density on the paper. Then, the background image after the gradation correction is processed by the error diffusion processing unit 3.
2 is output. For example, the gradation correction unit 5
(Lookup table) or the like. Of course, in addition to the LUT, the present invention may be realized by another method that can obtain the same effect. For example, a method of performing a conversion process of an input pixel value by a predetermined function may be used.

The error diffusion processing section 32 binarizes the background image received from the gradation correction section 5 with the output resolution. In this example, the binarization employs an error diffusion method. Of course, another binarization method may be adopted.

Next, an example of the operation of the image processing apparatus according to the fifth embodiment of the present invention will be described. First, rasterized document image data to be printed out from the outside, a background image, and a mask image to be embedded in the background image are input to the image input unit 1, and stored in the page buffer 2, the background image memory 3, and the mask image memory 7, respectively. Is stored. Here, the document image data and the background image are multi-valued image data of 8 bits (256 levels) per pixel, and the mask image data is binary image data. The background image and the mask image may be input in advance.

When the input of each image data is completed, the generation and synthesis processing of the background pattern is started. The background image read from the background image memory 3 is input to the halftone processing unit 6 and the gradation correction unit 5. The halftone processing unit 6 performs a halftone generation process on the input background image with a lower screen ruling than the screen ruling of the output device 13, and outputs the halftone-converted background image to the selecting unit 9. Here, the halftone-converted background image output from the halftone generation unit 6 has a pixel value of a black pixel = 255 and a pixel value of a white pixel, for example, when the gradation level can take a value of 0 to 255. = 0.

The tone correcting section 5 performs a tone correcting process on the input background image and outputs the result to the error diffusion processing section 32.
The error diffusion processing unit 32 binarizes the background image subjected to the gradation correction processing by the error diffusion processing. By the gradation correction processing in the gradation correction unit 5, the density of the background image subjected to the error diffusion processing and the background image subjected to the halftone processing input to the selection unit 9 is substantially equal to the density reproduced on the paper. I have to. For example, the gradation correction processing may be performed on the background image as described with reference to FIG. In this case, a process is performed so that the density of the image of the background portion binarized by the error diffusion processing unit 32 approaches the density of the latent image portion subjected to the halftone processing. Thereby, the output device 1
3 makes the latent image characters embedded in the background of the document less conspicuous, for example, on the paper printed out. The background image after the error diffusion processing output from the error diffusion processing unit 32 has, for example, a gradation level of 0 to 255.
In this case, the pixel value of the black pixel is expressed as 255, and the pixel value of the white pixel is expressed as 0.

In parallel with the above-described processing, a mask image is read from the mask image memory 7 and input to the selection unit 9. The selection unit 9 determines whether the background image subjected to the error diffusion processing by the error diffusion processing unit 32 or the background image subjected to the halftone processing by the halftone processing unit 6 in accordance with the value of each pixel of the input mask image. One of the corresponding pixels is selected and output. For example, when the mask image is a white pixel, the corresponding pixel data of the background image subjected to error diffusion processing is selected, and when the mask image is a black pixel, the corresponding pixel data of the background image subjected to halftone processing is output. can do. As a result, the image data output from the selection unit 9 becomes a background image (latent image embedded background image) in which only the area corresponding to the black area (latent image) of the mask image is embedded with a halftone dot pattern. This latent image embedded background image is output to the synthesizing unit 11.

The document image data read from the page buffer 2 is input to the synthesizing unit 11 in parallel.
The synthesizing unit 11 performs a synthesizing process by comparing the pixel values of the document image data and the latent image embedded background image, and selects the larger one of the pixel values, and outputs the result to the screen processing unit 31. The screen processing unit 31 converts the multi-valued image data input by a screen process such as an error diffusion process into binary image data. Then, the image data subjected to the error diffusion processing according to the pixel values 0 and 1 is printed out on a sheet by the output device 13.

At this time, since the latent image portion (halftone-processed portion) in the latent image-embedded background image has a gradation value of 0 or 255, the screen processing unit 31 performs an error diffusion process or an analog screen process. Even if the process is performed, the halftone dot pattern is reproduced on a sheet by the output device 13 without being destroyed. Background part other than latent image part (multi-valued background image)
Are subjected to error diffusion processing and analog screen processing by the screen processing unit 31, and are reproduced as random isolated dot patterns on paper. Since the latent image portion and the background portion have been processed so that the reproduction densities on the paper are substantially the same by the gradation correction process, the latent image portion is almost inconspicuous.

In the above example, the background image after the error diffusion processing by the error diffusion processing unit 32 and the background image after the halftone processing by the halftone processing unit 6 have, for example, a gradation level of 0 to 25.
In the case where a value of 5 can be taken, the pixel value of the black pixel = 255,
The description has been made assuming that the pixel value of the white pixel is expressed as 0. Other than this, for example, the pixel value of the black pixel =
1, the pixel value of the white pixel = 0, and the document image data is also binarized to values of 0 and 1 by, for example, error diffusion processing before being stored in the page buffer 2 or after being read from the page buffer 2. You can keep it. In this case, the synthesizing unit 11 can synthesize the document image data and the latent image-embedded background image by logical OR.
For example, when outputting to the binary output device 13, a light gray pattern image is synthesized on the background of the printed document, and when this pattern is copied, the embedded latent image character appears. Will be.

In FIG. 12, the resolution converters 4 and 8, the color discriminator 10, the control panel 14, the controller 15 and the like shown in the first embodiment are not shown, but they are not shown. Can be provided. In addition, this fifth
In this embodiment, the same modification as in the above-described second embodiment can be made. Of course, other various modifications are possible.

FIG. 13 is a block diagram showing a sixth embodiment of the image processing apparatus of the present invention. In the figure, FIG. 1, FIG.
0 and the same parts as those in FIG. In the sixth embodiment, the tone correction unit 5 of the fifth embodiment is arranged before the halftone processing unit 6,
An example is shown in which a gradation correction process is performed on a background image input to the dot processing unit 6.

The gradation correcting section 5 performs a halftone processing on the background image stored in the background image memory 3 by the halftone processing section 6 (an image serving as a latent image), The tone correction process is performed so that the background image subjected to the error diffusion process by the processing unit 32 is reproduced with substantially the same density on the paper. Then, the background image after the gradation correction is output to the halftone processing unit 6. The gradation correction unit 5 can be configured by, for example, an LUT (look-up table).
Of course, in addition to the LUT, the present invention may be realized by another method that can obtain the same effect. For example, a method of performing a conversion process of an input pixel value by a predetermined function may be used.

The error diffusion processing unit 32 is provided with the background image memory 3
Is binarized at the output resolution. In this example, the binarization employs an error diffusion method. Of course, another binarization method may be adopted.

Next, an example of the operation of the image processing apparatus according to the sixth embodiment of the present invention will be described. First, rasterized document image data to be printed out from the outside, a background image, and a mask image to be embedded in the background image are input to the image input unit 1, and stored in the page buffer 2, the background image memory 3, and the mask image memory 7, respectively. Is stored. Here, the document image data and the background image are multi-valued image data of 8 bits (256 levels) per pixel, and the mask image data is binary image data. The background image and the mask image may be input in advance.

When the input of each image data is completed, the process of generating and synthesizing the background pattern is started. The background image read from the background image memory 3 is input to the error diffusion processing unit 32 and the gradation correction unit 5. The error diffusion processing unit 32 binarizes the background image read from the background image memory 3 by an error diffusion process. The background image after the error diffusion processing output from the error diffusion processing unit 32 has a pixel value of a black pixel = 255 and a pixel value of a white pixel, for example, when the gradation level can take a value of 0 to 255. = 0.

The tone correcting section 5 performs a tone correcting process on the input background image and outputs the result to the halftone processing section 6. By the gradation correction processing in the gradation correction unit 5, the density of the background image subjected to the error diffusion processing and the background image subjected to the halftone processing input to the selection unit 9 is substantially equal to the density reproduced on the paper. I have to. For example, the gradation correction processing may be performed on the background image as described with reference to FIG. This makes the latent image characters embedded in the background of the document less conspicuous on paper printed and output from the output device 13, for example.

The halftone processing unit 6 performs a halftone generation process for the input background image with a screen ruling lower than the screen ruling of the output device 13, and selects the halftone-dotted background image to the selecting unit 9.
Output to Here, the halftone-converted background image output from the halftone generation unit 6 has a pixel value of a black pixel = 255 and a pixel value of a white pixel, for example, when the gradation level can take a value of 0 to 255. = 0.

In parallel with the above-described processing, a mask image is read from the mask image memory 7 and input to the selection unit 9. The selection unit 9 determines whether the background image subjected to the error diffusion processing by the error diffusion processing unit 32 or the background image subjected to the halftone processing by the halftone processing unit 6 in accordance with the value of each pixel of the input mask image. One of the corresponding pixels is selected and output. For example, when the mask image is a white pixel, the corresponding pixel data of the background image subjected to error diffusion processing is selected, and when the mask image is a black pixel, the corresponding pixel data of the background image subjected to halftone processing is output. can do. As a result, the image data output from the selection unit 9 becomes a background image (latent image embedded background image) in which only the area corresponding to the black area (latent image) of the mask image is embedded with a halftone dot pattern. This latent image embedded background image is output to the synthesizing unit 11.

The synthesizing unit 11 receives the document image data read from the page buffer 2 in parallel.
The synthesizing unit 11 performs a synthesizing process by comparing the pixel values of the document image data and the latent image embedded background image, and selects the larger one of the pixel values, and outputs the result to the screen processing unit 31. The screen processing unit 31 converts the multi-valued image data input by a screen process such as an error diffusion process into binary image data. Then, the image data subjected to the error diffusion processing according to the pixel values 0 and 1 is printed out on a sheet by the output device 13.

At this time, since the latent image portion (halftone-processed portion) in the latent image-embedded background image has a gradation value of 0 or 255, the screen processing unit 31 performs error diffusion processing or analog screen processing. Even if the process is performed, the halftone dot pattern is reproduced on a sheet by the output device 13 without being destroyed. Background part other than latent image part (multi-valued background image)
Are subjected to error diffusion processing and analog screen processing by the screen processing unit 31, and are reproduced as random isolated dot patterns on paper. Since the latent image portion and the background portion have been processed so that the reproduction densities on the paper are substantially the same by the gradation correction process, the latent image portion is almost inconspicuous.

In the above example, the background image after the error diffusion processing by the error diffusion processing section 32 and the background image after the halftone processing by the halftone processing section 6 have, for example, gradation levels of 0 to 25.
In the case where a value of 5 can be taken, the pixel value of the black pixel = 255,
The description has been made assuming that the pixel value of the white pixel is expressed as 0. Other than this, for example, the pixel value of the black pixel =
1, the pixel value of the white pixel = 0, and the document image data is also binarized to values of 0 and 1 by, for example, error diffusion processing before being stored in the page buffer 2 or after being read from the page buffer 2. You can keep it. In this case, the synthesizing unit 11 can synthesize the document image data and the latent image-embedded background image by logical OR.
For example, when outputting to the binary output device 13, a light gray pattern image is synthesized on the background of the printed document, and when this pattern is copied, the embedded latent image character appears. Will be.

In FIG. 13, the resolution converters 4 and 8, the color discriminator 10, the control panel 14, the controller 15 and the like shown in the first embodiment are not shown, but they are appropriately shown. Can be provided. In addition, this sixth
In this embodiment, the same modification as in the above-described second embodiment can be made. Of course, other various modifications are possible.

FIG. 14 is a block diagram showing a seventh embodiment of the image processing apparatus according to the present invention. In the figure, FIG. 1, FIG.
13 are denoted by the same reference numerals, and description thereof will be omitted. In the seventh embodiment, an example is shown in which both the tone correction processing on the error diffusion processing side in the fifth embodiment and the tone correction processing on the halftone processing side in the sixth embodiment are performed. .

The first gradation correction section 5-1 performs gradation correction processing on the background image stored in the background image memory 3 and sends the background image after gradation correction to the error diffusion processing section 32. Output. The second tone correction unit 5-2 performs tone correction processing on the background image stored in the background image memory 3 and outputs the background image after the tone correction to the halftone processing unit 6. I do. The first and second tone correction units 5-1 and 5-2 perform a background image (image serving as a latent image) on which the halftone processing has been performed by the halftone processing unit 6 and an error diffusion process on the error diffusion processing unit 32. The tone correction processing is performed so that the reproduced background image is reproduced with substantially the same density on the paper. The first and second tone correction units 5-1 and 5-2 can be configured by, for example, an LUT (lookup table). Of course, in addition to the LUT, the present invention may be realized by another method that can obtain the same effect. For example, a method of performing a conversion process of an input pixel value by a predetermined function may be used.

Next, an example of the operation of the image processing apparatus according to the seventh embodiment of the present invention will be described. First, rasterized document image data to be printed out from the outside, a background image, and a mask image to be embedded in the background image are input to the image input unit 1, and are respectively stored in the page buffer 2, the background image memory 3, and the mask image memory 7. Is stored. Here, the document image data and the background image are multi-valued image data of 8 bits (256 levels) per pixel, and the mask image data is binary image data. The background image and the mask image may be input in advance.

When the input of each image data is completed, the process of generating and synthesizing the background pattern is started. The background image read from the background image memory 3 is input to the first gradation correction unit 5-1 and the second gradation correction unit 5-2. The first gradation correction unit 5-1 performs gradation correction processing on the input background image, and outputs the result to the error diffusion processing unit 32. The error diffusion processing unit 32 binarizes the background image whose gradation has been corrected by error diffusion processing. The background image after the error diffusion processing output from the error diffusion processing unit 32 has a pixel value of a black pixel = 255 and a pixel value of a white pixel, for example, when the gradation level can take a value of 0 to 255. = 0
It is expressed as

The second tone correction section 5-2 performs tone correction processing on the input background image and outputs the result to the halftone processing section 6. The halftone processing unit 6 performs a halftone generation process with a line frequency lower than the screen frequency of the output device 13 on the gradation-corrected background image, and outputs the halftone-converted background image to the selection unit 9. I do. Here, the halftone-converted background image output from the halftone generation unit 6 has a pixel value of a black pixel = 255 and a pixel value of a white pixel, for example, when the gradation level can take a value of 0 to 255. = 0.

By the gradation correction processing in the first and second gradation correction units 5-1 and 5-2, both the error diffusion processed background image input to the selection unit 9 and the halftone processed background image are input. The density reproduced on the paper is made almost equal. This makes the latent image characters embedded in the background of the document less conspicuous on paper printed and output from the output device 13, for example. In this case, the gradation correction processing enables correction to an arbitrary gradation curve.

In parallel with the above-described processing, a mask image is read from the mask image memory 7 and input to the selection unit 9. The selection unit 9 determines whether the background image subjected to the error diffusion processing by the error diffusion processing unit 32 or the background image subjected to the halftone processing by the halftone processing unit 6 in accordance with the value of each pixel of the input mask image. One of the corresponding pixels is selected and output. For example, when the mask image is a white pixel, the corresponding pixel data of the background image subjected to error diffusion processing is selected, and when the mask image is a black pixel, the corresponding pixel data of the background image subjected to halftone processing is output. can do. As a result, the image data output from the selection unit 9 becomes a background image (latent image embedded background image) in which only the area corresponding to the black area (latent image) of the mask image is embedded with a halftone dot pattern. This latent image embedded background image is output to the synthesizing unit 11.

The image data read from the page buffer 2 is input to the synthesizing unit 11 in parallel.
The synthesizing unit 11 performs a synthesizing process by comparing the pixel values of the document image data and the latent image embedded background image, and selects the larger one of the pixel values, and outputs the result to the screen processing unit 31. The screen processing unit 31 converts the multi-valued image data input by a screen process such as an error diffusion process into binary image data. Then, the image data subjected to the error diffusion processing according to the pixel values 0 and 1 is printed out on a sheet by the output device 13.

At this time, since the latent image portion (halftone-processed portion) in the latent image-embedded background image has a gradation value of 0 or 255, the screen processing unit 31 performs an error diffusion process or an analog screen process. Even if the process is performed, the halftone dot pattern is reproduced on a sheet by the output device 13 without being destroyed. Background part other than latent image part (multi-valued background image)
Are subjected to error diffusion processing and analog screen processing by the screen processing unit 31, and are reproduced as random isolated dot patterns on paper. Since the latent image portion and the background portion have been processed so that the reproduction densities on the paper are substantially the same by the gradation correction process, the latent image portion is almost inconspicuous.

In the above example, the background image after the error diffusion processing by the error diffusion processing section 32 and the background image after the halftone processing by the halftone processing section 6 have, for example, gradation levels of 0 to 25.
In the case where a value of 5 can be taken, the pixel value of the black pixel = 255,
The description has been made assuming that the pixel value of the white pixel is expressed as 0. Other than this, for example, the pixel value of the black pixel =
1, the pixel value of the white pixel = 0, and the document image data is also binarized to values of 0 and 1 by, for example, error diffusion processing before being stored in the page buffer 2 or after being read from the page buffer 2. You can keep it. In this case, the synthesizing unit 11 can synthesize the document image data and the latent image-embedded background image by logical OR.
For example, when outputting to the binary output device 13, a light gray pattern image is synthesized on the background of the printed document, and when this pattern is copied, the embedded latent image characters emerge. Will be.

In FIG. 14, the resolution converters 4 and 8, the color discriminator 10, the control panel 14, the controller 15 and the like shown in the first embodiment are not shown, but they are appropriately shown. Can be provided. In addition, this seventh
In this embodiment, the same modification as in the above-described second embodiment can be made. Of course, other various modifications are possible.

FIG. 15 is a block diagram showing an eighth embodiment of the image processing apparatus according to the present invention. In the figure, FIG. 1, FIG.
1 to 14 are denoted by the same reference numerals and description thereof is omitted. 33 is a first background image memory, and 34 is a second background image memory. In the eighth embodiment, an example is shown in which a background image that has been subjected to gradation correction processing is prepared in a memory.

The first background image memory 33 stores the first background image. The second background image memory 34 stores a second background image. The first background image and the second background image are:
The first background image is subjected to error diffusion processing by the error diffusion processing unit 32, and the second background image is subjected to halftone processing by the halftone processing unit 6, respectively. For example, when printed out on paper,
The gradation is corrected so that the densities reproduced on the paper become almost equal. This makes it possible to make the latent image characters embedded in the background of the document less noticeable on the printed paper. Note that either the first background image or the second background image may have the same gradation as the original background image, or both may be gradation corrected images of the original background image. You may.

The error diffusion processing section 32 performs error diffusion processing on the first background image stored in the first background image memory 33 and outputs the result to the selection section 9. Also, the dot processing unit 6
Performs halftone processing on the second background image stored in the second background image memory 34 and outputs the result to the selection unit 9.

Next, an example of the operation of the image processing apparatus according to the eighth embodiment of the present invention will be described. First, rasterized document image data to be printed out from the outside, a first background image, a second background image, and a mask image to be embedded in the background image are input to the image input unit 1, and the page buffer 2 and the first background, respectively. Image memory 33, second
It is stored in the background image memory 34 and the mask image memory 7. Here, the document image data, the first background image, and the second background image are multi-valued image data of 8 bits per pixel (256 levels), and the mask image data is binary image data.
Note that the first background image, the second background image, and the mask image may be input in advance.

When the input of each image data is completed, the generation and synthesis processing of the background pattern is started. The first background image read from the first background image memory 33 is input to the error diffusion processing unit 32. The error diffusion processing unit 32 binarizes the first background image by error diffusion processing. The background image after the error diffusion processing output from the error diffusion processing unit 32 has, for example, a gradation level of 0 to 0.
When the value of 255 can be taken, the pixel value of the black pixel = 25
5, the pixel value of the white pixel = 0.

The second background image read from the second background image memory 34 is input to the halftone processing unit 6. The halftone processing unit 6 performs a halftone generation process on the second background image with a line frequency lower than the screen frequency of the output device 13,
The halftone-dotted background image is output to the selection unit 9. Here, the halftone-converted background image output from the halftone generation unit 6 has a pixel value of a black pixel = 255 and a pixel value of a white pixel, for example, when the gradation level can take a value of 0 to 255. = 0.

As described above, the first background image and the second background image are subjected to the error diffusion processing of the first
The gradation of the background image and the halftone-processed second background image are corrected in advance so that the densities reproduced on the paper are substantially equal. This makes the latent image characters embedded in the background of the document less noticeable on the paper printed out from the output device 13 for example.

In parallel with the above-described processing, a mask image is read from the mask image memory 7 and input to the selection unit 9. In the selecting unit 9, the first background image subjected to the error diffusion processing in the error diffusion processing unit 32 and the first background image subjected to the halftone processing in the halftone processing unit 6 in accordance with the value of each pixel of the input mask image. 2
One of the corresponding pixels of the background image is selected and output. For example, if the mask image is a white pixel, the corresponding pixel data of the first background image subjected to the error diffusion processing is selected, and if the mask image is a black pixel, the second pixel data subjected to the halftone processing is selected.
The corresponding pixel data of the background image can be output. As a result, the image data output from the selection unit 9 is
Background image (latent image embedded background image) embedded with a halftone dot pattern only in the area corresponding to the black area (latent image) of the mask image
Becomes This latent image embedded background image is output to the synthesizing unit 11.

The synthesizing unit 11 receives the document image data read from the page buffer 2 in parallel.
The synthesizing unit 11 performs a synthesizing process by comparing the pixel values of the document image data and the latent image embedded background image, and selects the larger one of the pixel values, and outputs the result to the screen processing unit 31. The screen processing unit 31 converts the multi-valued image data input by a screen process such as an error diffusion process into binary image data. Then, the image data subjected to the error diffusion processing according to the pixel values 0 and 1 is printed out on a sheet by the output device 13.

At this time, since the latent image portion (halftone-processed portion) in the latent image-embedded background image has a gradation value of 0 or 255, the screen processing unit 31 performs a screen process such as an error diffusion process. Even if the process is performed, the halftone dot pattern is reproduced on a sheet by the output device 13 without being destroyed. The background portion (multi-valued background image) other than the latent image portion is subjected to error diffusion processing and analog screen processing by the screen processing section 31, and is reproduced on a sheet as a random isolated dot pattern. Since the gradation correction processing has been performed in advance so that the reproduction densities of the latent image portion and the background portion on the paper substantially match, the latent image portion is almost inconspicuous.

In the above example, the first background image after the error diffusion processing by the error diffusion processing unit 32 and the second background image after the halftone processing by the halftone processing unit 6 have, for example, gradation levels of 0 to 0. When a value of 255 can be taken, a pixel value of a black pixel =
The description has been made assuming that the pixel value of the white pixel is equal to 255. In addition, for example, the pixel value of the black pixel is set to 1 and the pixel value of the white pixel is set to 0, and the document image data is also stored before or after being read from the page buffer 2. It can be binarized to values of 0 and 1 by error diffusion processing or the like. In this case, the synthesizing unit 11 can synthesize the document image data and the latent image-embedded background image by logical OR. For example, when outputting to the binary output device 13, a light gray pattern image is synthesized on the background of the printed document, and when this pattern is copied, the embedded latent image characters emerge. Will be.

Although FIG. 15 does not show the resolution conversion units 4 and 8, the color identification unit 10, the control panel 14, the control unit 15 and the like shown in the first embodiment, they are appropriately shown. Can be provided. In addition, this eighth
In this embodiment, the same modification as in the above-described second embodiment can be made. Of course, other various modifications are possible.

FIG. 16 is a block diagram showing a ninth embodiment of the image processing apparatus according to the present invention. In the figure, FIG. 1, FIG.
1 to 15 are denoted by the same reference numerals, and description thereof will be omitted. The ninth embodiment shows an example in which a background image that has been subjected to gradation correction processing, error diffusion processing or halftone processing is prepared in a memory in advance.

The first background image memory 33 stores a first background image that has been subjected to gradation correction processing and error diffusion processing in advance. The second background image memory 34 stores a second background image that has been subjected to gradation correction processing and halftone processing in advance. First
The background image and the second background image are created from the same background image, and for example, when printed out on paper, gradation correction is performed so that the densities reproduced on paper are almost equal. ing. This makes it possible to make the latent image characters embedded in the background of the document less noticeable on the printed paper. The first
Either the background image or the second background image may have the same gradation as the original background image, or both may be gradation corrected images of the original background image.

The selection section 9 includes the first background image stored in the first background image memory 33 and the second background image memory 3.
The second background image stored in the mask image memory 7 is input, and one of them is selected according to the mask image stored in the mask image memory 7.

Next, an example of the operation of the image processing apparatus according to the ninth embodiment of the present invention will be described. First, rasterized document image data to be printed out from the outside, a first background image, a second background image, and a mask image to be embedded in the background image are input to the image input unit 1, and the page buffer 2 and the first background, respectively. Image memory 33, second
It is stored in the background image memory 34 and the mask image memory 7. Here, the document image data is 8 bits per pixel (256 bits).
Level) multi-valued image data, the first background image, the second
The background image is expressed, for example, as a pixel value of a black pixel = 255 and a pixel value of a white pixel = 0. The mask image data is binary image data. Note that the first background image and the second
The background image and the mask image are preferably input in advance.

When the input of each image data is completed, the generation and synthesis processing of the background pattern is started. The first background image is read from the first background image memory 33, the second background image is read from the second background image memory 34, and the mask image is read from the mask image memory 7 and input to the selection unit 9. Is done. In the selection unit 9,
The first background image read from the first background image memory 33 and the second background image are read in accordance with the value of each pixel of the input mask image.
One of the second background images read from the background image memory 34 is selected and output. For example, when the mask image is a white pixel, the pixel data of the first background image is selected,
When the mask image is a black pixel, the pixel data of the second background image can be output. As a result, the image data output from the selection unit 9 becomes a background image (latent image embedded background image) in which only the area corresponding to the black area (latent image) of the mask image is embedded with a halftone dot pattern. This latent image embedded background image is output to the synthesizing unit 11.

As described above, the first background image and the second background image are subjected to the error diffusion processing of the first
The gradation of the background image and the halftone-processed second background image are corrected in advance so that the densities reproduced on the paper are substantially equal. This makes the latent image characters embedded in the background of the document less noticeable on the paper printed out from the output device 13 for example.

The synthesizing unit 11 receives the document image data read from the page buffer 2 in parallel.
The synthesizing unit 11 performs a synthesizing process by comparing the pixel values of the document image data and the latent image embedded background image, and selects the larger one of the pixel values, and outputs the result to the screen processing unit 31. The screen processing unit 31 converts the multi-valued image data input by a screen process such as an error diffusion process into binary image data. Then, the image data subjected to the error diffusion processing according to the pixel values 0 and 1 is printed out on a sheet by the output device 13.

At this time, since the latent image portion (halftone-processed portion) in the latent image-embedded background image has a gradation value of 0 or 255, the screen processing unit 31 performs a screen process such as an error diffusion process. Even if the process is performed, the halftone dot pattern is reproduced on a sheet by the output device 13 without being destroyed. The background portion (multi-valued background image) other than the latent image portion is subjected to error diffusion processing and analog screen processing by the screen processing section 31, and is reproduced on a sheet as a random isolated dot pattern. Since the gradation correction processing has been performed in advance so that the reproduction densities of the latent image portion and the background portion on the paper substantially match, the latent image portion is almost inconspicuous.

In the above-mentioned example, the first background image in the first background image memory 33 and the second background image in the second background image memory 34 can have, for example, a gradation level of 0 to 255. In this case, it has been described that the pixel value of the black pixel is expressed as 255 and the pixel value of the white pixel is expressed as 0. In addition, for example, the pixel value of the black pixel is set to 1 and the pixel value of the white pixel is set to 0, and the document image data is also stored before or after being read from the page buffer 2. It can be binarized to values of 0 and 1 by error diffusion processing or the like. in this case,
The synthesizing unit 11 can synthesize the document image data and the latent image-embedded background image by the logical OR. For example, 2
When outputting to the value output device 13, a light gray pattern image is synthesized on the background of the printed document, and when this pattern is copied, the embedded latent image characters emerge. Become.

In the ninth embodiment, halftone processing or error diffusion processing is performed in advance, and these processings need not be performed at the time of synthesizing with document image data. Higher speed can be achieved.

In the ninth embodiment, the background image after the error diffusion processing is stored as the first background image, and the background image after the halftone processing is stored as the second background image. For example, a background image subjected to tone correction before error diffusion processing is stored as the first background image and the error diffusion processing unit 32 is provided, or tone correction before halftone processing is applied as the second background image. A configuration in which a background image is stored and the dot processing unit 6 is provided is also possible.

Although the resolution converters 4 and 8, the color discriminator 10, the control panel 14, and the controller 15 shown in the first embodiment are not shown in FIG. Can be provided. In addition, this ninth
In this embodiment, the same modification as in the above-described second embodiment can be made. Of course, other various modifications are possible.

In each of the above embodiments, the background image or the first and second background images and the mask image need not be images having the same size as the document image data. For example, a small background image or first and second background images and a mask image can be repeatedly used for one page of document image data. FIG. 17 is an explanatory diagram of an example of a process of creating a latent image embedded background image when a small background image and a mask image are used repeatedly. For example, the first embodiment will be described with reference to FIG.
It is assumed that a background image shown in FIG. 17 and a mask image shown in FIG. The background image and the mask image input at this time are smaller than, for example, the image for one page shown in FIG.

A gradation correction process is performed on such a small background image to create background images having different densities as shown in FIG. 17B, and further subjected to halftone processing. And
Based on the mask image shown in FIG. 17C, one of a background image shown in FIG. 17A and a background image obtained by performing halftone processing on the image after gradation correction shown in FIG. The selection unit 9 makes a selection to generate a latent image embedded background image as shown in FIG. In the latent image-embedded background image shown in FIG. 17D, the tone correction process is performed so that the density of the background portion and the halftone dot portion are substantially the same at the time of printing. Since the density should be the same, the background portion and the latent image portion are apparently indistinguishable. However, in FIG. 17D, different hatchings are applied to show the difference so that the latent image portion and the background portion can be seen.

Such a small latent image-embedded background image may be repeatedly generated and arranged in a tile shape, for example, as shown in FIG. Actually, for example, the reading of the background image and the mask image for one line is repeatedly performed to generate one line for one page, and the generation processing for each line is repeated to perform the latent processing for one page. An image-embedded background image may be generated. Of course, the generation of the latent image-embedded background image for each line and the synthesis with the document image data may be performed simultaneously.

By repeating the small latent image-embedded background image to fill the page, the background image memory 3 for storing the background image and the mask image or the first background image memory 33 and the second background image memory 34, and The capacity of the mask image memory 7 can be reduced. In particular, in the above-described eighth and ninth embodiments, since two background images are held, the effect of reducing the memory capacity by holding a background image smaller than one page as described above is great.

The size of the background image and the size of the mask image do not need to match. For example, if the background image has a uniform density, only the density value can be stored in the background image memory 3. It is. In the above description, the description has been given according to the first embodiment.
The same applies to the embodiment.

FIG. 18 is an explanatory diagram of an example of a storage medium storing a computer program when the functions of the image processing apparatus of the present invention are realized by a computer program. In the figure, 41 is a program, 42 is a computer,
51 is a magneto-optical disk, 52 is an optical disk, 53 is a magnetic disk, 54 is a memory, 61 is a magneto-optical disk device,
62 is an optical disk device, and 63 is a magnetic disk device.

The functions in the configurations shown in the above embodiments of the present invention can also be realized by a program 41 executable by a computer. In that case, the program 41 and data used by the program can be stored in a computer-readable storage medium. A storage medium is a type of signal corresponding to a change state of energy such as magnetism, light, electricity, etc., caused to a reading device provided in a hardware resource of a computer in accordance with a description content of a program. Thus, the program description can be transmitted to the reading device. For example, a magneto-optical disk 51,
An optical disk 52, a magnetic disk 53, a memory 54, etc. Of course, these storage media are not limited to portable types.

The program 41 is stored in these storage media. For example, the magneto-optical disk device 61, the optical disk device 62, the magnetic disk device 63,
Alternatively, by attaching these storage media to a memory slot (not shown), the program 41 is read from the computer, and the functions of the configurations described in the embodiments of the present invention can be executed. Alternatively, a storage medium may be mounted on the computer 42 in advance, the program 41 may be transferred to the computer 42 via a network or the like, and the program 41 may be stored in the storage medium and executed.

FIG. 19 is a block diagram showing an example of a system to which the image processing device of the present invention is applied. In the figure, 71 is a client PC, 72 is a printer controller, 73 is a printer, and 74 is a network. Client P
C71 and the printer controller 72 are connected to a network 74.
Connected by The print data transmitted from the client PC 71 to the printer controller 72 is
The image data is decomposed in the printer controller 72 and output to the printer 73 as raster image data. Then, the image is processed by the image processing apparatus of the present invention provided inside the printer 73, and then printed out on paper.

In the system having such a configuration, the background image and the mask image are transferred to the printer 73 and registered in advance. When the print data is transferred from the client PC 71 to the printer controller 72 and the raster image data is transferred to the printer 73, the printer 73
Inside, the latent image-embedded background image and the raster image data are combined as described in each of the above embodiments, and printed on paper. When the image printed in this way is copied, a latent image appears on the copied image. In this way, it is possible to prevent unauthorized copying and the like.

FIG. 20 is a block diagram showing another example of a system to which the image processing apparatus of the present invention is applied. In the figure, FIG.
The same parts as those described above are denoted by the same reference numerals and description thereof will be omitted. 8
1 is an application program, 82 is an operating system, and 83 is a device driver. FIG.
In the example shown in (1), an example in which the image processing apparatus of the present invention is provided in the printer 73 is shown. However, the present invention is not limited to this. For example, the function of the image processing apparatus of the present invention may be configured to be executed by the device driver 83 in the client PC 71. In the client PC 71, usually, document data to be printed is generated by the application program 81. When the user instructs print output of the generated document image data, the document data is transferred to the operating system 82, and the operating system 82 transfers the received document data to the device driver 83 corresponding to the device to be output.

The device driver 83 receives instructions of a background image and a mask image in advance or at the time of a print instruction,
A latent image-embedded background image is generated by the processing described in the first to ninth embodiments, and the latent image-embedded background image is used as print data together with the document data to be printed as the printer controller 72 or the direct printer 73.
Transfer to When the document data is not an image, the document data is transferred as print data without combining the latent image-embedded background image and the document data by the combining unit 11. Of course, if the document data is an image, it may be combined and transferred. For the instruction of the background image, for example, a density value may be set. Alternatively, a file name in which a background image is stored may be set. Further, the instruction of the mask image may be set, for example, by setting a character string, a file name storing drawing data, or the like.

FIG. 21 is a flowchart showing an example of the operation of the printer driver in another example of the system to which the image processing apparatus of the present invention is applied. When the document data created by the application program 81 is transferred to the device driver 83 via the operating system 82, the processing shown in FIG. 21 is started.

First, in S91, the received document data is converted into data that can be interpreted by the printer 73 or the printer controller 72 that outputs the document data. Printer 7
Here, the data that can be interpreted by the printer controller 3 or the printer controller 72 is PDL data.
Of course, it is not limited to this.

Next, in S92, a drawing process is performed based on a preset character string and drawing data to generate a mask image. When drawing a character string, first, a memory area corresponding to the length of the character string is secured, and the character string is drawn therein, thereby generating a mask image. Here, it is needless to say that the size of the mask image is a size that can accommodate the drawn character string, but it is desirable that the size of the mask image be a multiple of the size of the dither matrix used in the halftone processing. . By using a multiple of the size of the dither matrix used in the halftone processing, for example, FIG.
As described in FIG. 7, when arranging small latent image-embedded background images, it is possible to prevent mismatching at the joint.

Next, in S93, a background image is created based on a preset density value. For example, S9
A background image can be created by securing a memory area of the same size as the mask image created in step 2 and filling the memory area with the set pixel values.

Next, in S94, a halftone dot generating process is performed. First, a memory area of the same size as the background image generated in S93 is secured, the background image is read, a predetermined dither matrix is applied, and a halftone image generation process is performed. The processed image data is stored in the secured memory area.

Next, in step S95, an error diffusion process is performed. First, a memory area of the same size as the background image generated in S93 is secured, the background image is read, and error diffusion processing is performed. The processed image data is stored in the secured memory area.

Prior to the dot generation processing in S94 or the error diffusion processing in S95, a predetermined offset value is added to each pixel value of one or both of the background images to be processed. This offset value is a value set in advance so that the halftone image and the error diffusion image have the same reproduction density on paper. That is, gradation correction processing is performed by adding an offset value.

Either of steps S94 and S95 may be performed first, or they may be performed in parallel. Further, when the error diffusion processing is not performed as in the above-described first to third embodiments of the present invention, the processing in S95 is not necessary.

Next, in S96, a process of generating a latent image embedded background image is performed. First, a memory area having the same size as the mask image generated in S92 is secured. Next, the mask image is read out one pixel at a time, and if the pixel is a black pixel, the pixel value of the halftone image at the same position is read out and stored at the same position in the secured memory area. If the pixel is a white pixel, an error diffusion image at the same position (or a background image or a background image to which an offset value is added) is read and stored at the same position in the secured memory area. By this synthesis processing,
A latent image embedded background image having the same size as the mask image generated in S92 is generated. Here, the page is smaller than one page, and is called a partial latent image embedded background image.

Next, in S97, the partial latent image embedded background image generated in S96 is repeatedly processed so as to have the same size as the page size of the document data to be printed. First, the output paper size and resolution of the document image are recognized, and the required memory size is calculated. The calculated memory size is secured, and the area shown in FIG.
FIG. 17 shows a partial latent image embedded background image as shown in FIG.
The image is copied so as to be arranged as shown in (E), and a latent image-embedded background image having a size of one page is generated. Or,
PD that repeatedly draws a partial latent image embedded background image
L data may be generated.

Next, in S98, the latent image embedding background image generated in S97 (or the partial latent image embedding background image and PD
L data) is added to the PDL data generated in S91 together with an image synthesis command. Here, the image combining command may be a command for combining the latent image-embedded background image with the image data of a predetermined color component among the KYMC components of the image of the decomposed document data by OR. If the predetermined color component is a K component, a gray latent image embedding background image is synthesized and printed out on the background of the document image, and if it is a C component, a light blue latent image embedding is embedded in the document image background. The background image is synthesized and printed out.

Finally, in S99, the PDL data of the document data to which the image synthesizing instruction and the latent image-embedded background image have been added is transmitted to the printer controller 72, and the processing in the device driver 83 ends. Upon receiving the PDL data, the printer controller 72 receives the received PDL data.
Decompose the L data to generate raster image data. At this time, the added latent image-embedded background image is combined with the rasterized document image data by the inserted image combining instruction, and the combined raster image data is output to the printer 73.

The device driver 83 which realizes the function of the image processing apparatus according to the present invention is, for example, shown in FIG.
Can be stored in a storage medium that can be read by a computer as described above, and the client PC 71 can operate by reading from the storage medium.

In the above description, the tone correction processing is performed by adding an offset value. However, the present invention is not limited to this, and the tone correction processing may be performed using an LUT or a function. Is also possible.

Further, in the above-described operation example, the example has been described in which the halftone dot image and the error diffusion image having the same size as the generated mask image are generated by the halftone dot generation process and the error diffusion process, respectively. A small halftone dot pattern and an isolated dot pattern are generated in advance, and are repeatedly arranged in a memory area of the same size as the mask image to generate a halftone dot image and an error diffusion image of the same size as the mask image. May be configured. In addition, FIG.
As shown in FIG. 6, a halftone image or an error diffusion image may be created in advance, and halftone processing or error diffusion processing may not be performed during actual output processing.

Furthermore, in the above-described operation example, the P image added with the combining instruction for combining the latent image embedded background image with the document data.
Although the description has been made assuming that the DL data is created, for example, the document data is rendered and converted into raster image data, combined with the latent image embedded background image, and then transferred to the printer 73 or the printer controller 72. You may.

In the above two system examples, an example in which the image processing apparatus of the present invention is applied to the printer 73 and an example in which the image processing apparatus of the present invention is applied to the device driver 83 of the client PC 71 are shown. It is also possible to apply an image processing device.

[0181]

As is apparent from the above description, according to the present invention, it is possible to create a document in which copying such as a confidential document is prohibited using ordinary paper as in the case of using copy forgery prevention paper. Can be. Thereby, for example, even if it is combined with a main image such as a document and recorded and output using normal paper,
The same effect as in the case of using copy forgery prevention paper can be obtained. At this time, by performing the gradation correction so that the density of the pattern serving as the latent image and the density of the background become substantially the same on the paper, the pattern of the latent image can be made as inconspicuous as possible. For the background part, it is possible to use the screen processing means that is normally used as it is, in which case it can be realized with a load of performing halftone processing for a latent image pattern, and Processing can be performed at a high speed in a small amount.

Further, it is possible to easily change the latent image pattern and the background pattern. For example, when creating multiple copies of documents, it is easy to combine different latent image patterns for each copy, reducing the management burden of managing copy and counterfeit prevention paper for each latent image pattern as in the past. can do. Also, whether the printer that prints confidential documents is a color printer or a black and white printer, it is possible to synthesize a background pattern containing a latent image in the same way,
The present invention has various effects.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a first embodiment of an image processing apparatus according to the present invention.

FIG. 2 is an explanatory diagram of an example of a background image.

FIG. 3 is an explanatory diagram of an example of a mask image.

FIG. 4 is an explanatory diagram of an example of a gradation correction process.

FIG. 5 is an enlarged view of an example of a latent image-embedded background image output from a selection unit 9;

FIG. 6 is an explanatory diagram of an example of an analog screen process.

FIG. 7 is an enlarged view of an example of an image printed on a sheet.

FIG. 8 is a block diagram illustrating a second embodiment of the image processing apparatus according to the present invention.

FIG. 9 is a partially enlarged view showing an example of an image before and after error diffusion processing.

FIG. 10 is a block diagram illustrating a third embodiment of the image processing apparatus according to the present invention.

FIG. 11 is a block diagram illustrating a fourth embodiment of the image processing apparatus according to the present invention.

FIG. 12 is a block diagram illustrating a fifth embodiment of the image processing apparatus according to the present invention.

FIG. 13 is a block diagram illustrating a sixth embodiment of the image processing apparatus according to the present invention.

FIG. 14 is a block diagram illustrating a seventh embodiment of the image processing apparatus according to the present invention.

FIG. 15 is a block diagram illustrating an image processing apparatus according to an eighth embodiment of the present invention.

FIG. 16 is a block diagram showing a ninth embodiment of the image processing apparatus of the present invention.

FIG. 17 is an explanatory diagram illustrating an example of a process of creating a latent image embedded background image when a small background image and a mask image are used repeatedly.

FIG. 18 is an explanatory diagram of an example of a storage medium storing a computer program when the functions of the image processing apparatus of the present invention are realized by the computer program.

FIG. 19 is a configuration diagram showing an example of a system to which the image processing device of the present invention is applied.

FIG. 20 is a configuration diagram showing another example of a system to which the image processing device of the present invention is applied.

FIG. 21 is a flowchart illustrating an example of an operation of a printer driver in another example of a system to which the image processing apparatus according to the invention is applied.

FIG. 22 is an explanatory diagram of an example of a print pattern of copy forgery prevention paper.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image input part, 2 ... Page buffer, 3 ... Background image memory, 4, 8 ... Resolution conversion part, 5 ... Gradation correction part, 5-1
.., A first tone correction section, 5-2 a second tone correction section, 6 a dot processing section, 7 a mask image memory, 9 a selection section, 10 a color identification section, 11 a synthesis section, 12. Analog screen generator (abbreviated as ASG), 13 output device, 14 control panel, 15 control unit, 21 storage unit, 22
... Image output order controller, 23 error diffusion processor, 31 screen processor, 32 error diffusion processor, 33 first background image memory, 34 second background image memory, 41 program, 42 computer , 51 ... magneto-optical disk,
52 optical disk, 53 magnetic disk, 54 memory, 61 magneto-optical disk device, 62 optical disk device, 63 magnetic disk device, 71 client P
C, 72: Printer controller, 73: Printer, 7
4 Network, 81 Application program, 82 Operating system, 83 Device driver.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04N 1/405 H04N 1/40 104 1/46 1/46 Z

Claims (37)

[Claims] An image processing apparatus for outputting a latent image-embedded background image in which a mask image is embedded as a latent image in a background image, a gradation correcting means for performing gradation correction of the background image, Halftone processing means for performing halftone processing on the background image after tone correction by the tone correction means with a rougher number of lines than the number of output lines, and a background image subjected to halftone processing by the halftone processing means or Selecting means for selecting any of the background images not subjected to halftone processing by the halftone processing means in accordance with the mask image and outputting a latent image embedded background image; An image characterized in that tone correction is performed so that the tone of the background image that has been subjected to halftone processing by the point processing means and the background image that has not been subjected to halftone processing by the halftone processing means substantially match at the time of output. Processing equipment. 2. The image processing apparatus according to claim 1, wherein the gradation correction unit performs gradation correction on the background image input to the halftone processing unit. 3. The image processing apparatus according to claim 1, further comprising: binarizing means for binarizing the background image with the number of output lines, wherein the output of the binarizing means is not subjected to halftone processing by the halftone processing means. The image processing apparatus according to claim 2, wherein the information is input to the selection unit. 4. The tone correcting means performs tone correction on the background image, and inputs the background image to the selecting means as a background image that has not been subjected to halftone processing by the halftone processing means. 2. The image processing apparatus according to claim 1, wherein the halftone processing unit performs halftone processing on the background image. 5. The method according to claim 1, further comprising the step of binarizing the background image whose gradation has been corrected by said gradation correcting means with the number of output lines and inputting it as a background image which has not been subjected to halftone processing by said halftone processing means. 2. The image processing apparatus according to claim 1, further comprising: a binarizing unit that performs halftone processing on the background image. 6. The gradation correction means, wherein the gradation correction is performed on the background image and input to the halftone dot processing means, and the gradation correction is separately performed on the background image and the gradation correction is performed by the selection means. 2. The image processing apparatus according to claim 1, wherein the image is input as a background image that has not been subjected to halftone processing by the halftone processing unit. 7. The background image subjected to gradation correction by the gradation correction means is binarized by the number of output lines and input to the selection means as a background image not subjected to halftone processing by the halftone processing means. The image processing apparatus according to claim 6, further comprising a binarization unit that performs binarization. 8. An image processing apparatus for outputting a latent image-embedded background image in which a mask image is embedded as a latent image in a background image, a first background image storage means for holding a first background image, and a second background Second background image holding means for holding an image, halftone processing means for performing halftone processing on the second background image with a line number coarser than the number of output lines, the first background image or the halftone Selecting means for selecting any of the second background images subjected to halftone processing by the point processing means in accordance with the mask image and outputting a latent image embedded background image, wherein the first background image and the In the second background image, when the same background image is subjected to the halftone processing by the halftone processing means and when the halftone processing is not performed by the halftone processing means, the gradation substantially coincides at the time of output. Characterized by being subjected to gradation correction so that Image processing device. 9. The apparatus according to claim 8, further comprising a binarizing unit for binarizing the first background image with the number of output lines and inputting the binarized image to the selecting unit as a first background image. Image processing device. 10. The method according to claim 3, wherein the binarizing means binarizes the background image or the first background image by an error diffusion method. The image processing apparatus according to any one of the preceding claims. 11. The halftone processing unit according to claim 1, wherein the halftone processing unit performs halftone processing by binarizing a background image or a second background image by a dither method. 2. The image processing device according to claim 1. 12. An image processing apparatus for outputting a latent image-embedded background image in which a mask image is embedded as a latent image in a background image, a first background image storing means for holding a first background image, and a second background. A second background image holding unit for holding an image, and a selection unit for selecting either the first background image or the second background image according to the mask image and outputting a latent image embedded background image The second background image is obtained by subjecting the same background image as the first background image to halftone processing with a line frequency that is coarser than the number of output lines. In the second background image, when the same background image is subjected to the halftone processing by the halftone processing means and when the halftone processing is not performed by the halftone processing means, the gradation substantially coincides at the time of output. Is characterized by being subjected to gradation correction Image processing device. 13. The first background image has an output line number of 2
13. The image processing apparatus according to claim 12, wherein the image is a binarized image. 14. An image processing apparatus for outputting a latent image-embedded background image in which a mask image is embedded as a latent image in a background image, wherein the background image is subjected to halftone processing with a rougher number of lines than the number of output lines. Halftone processing means, and selecting means for selecting any of the background image and the background image subjected to halftone processing by the halftone processing means in accordance with the mask image and outputting a latent image embedded background image. Characteristic image processing device. 15. The image processing apparatus according to claim 1, further comprising a synthesizing unit for synthesizing a main image with the latent image-embedded background image output from the selecting unit and outputting the main image.
5. The image processing device according to any one of 4. 16. A storage device capable of storing a plurality of latent image-embedded background images output from the selection device, and a specific latent image-embedded background from the latent image-embedded background images stored in the storage device. An image processing apparatus comprising: an instructing unit that instructs an image; and a combining unit that combines the latent image-embedded background image in the storage unit and the main image designated by the instructing unit and outputs the combined image as a combined image. The image processing apparatus according to claim 1. 17. The main image is a black-and-white image, the background image is a color image composed of three YMC components, and the synthesizing means outputs the main image as a K component image, and outputs a YMC component image. 17. The image processing apparatus according to claim 15, wherein a color component image corresponding to the latent image-embedded background image is output as the composite image. 18. The image processing apparatus according to claim 18, further comprising a color identification unit that identifies whether the main image is a black-and-white image or a color image, wherein the latent-image-embedded background image is a single-color image, When the main image is a black and white image according to the identification result by the color identification means, the latent image-embedded background image is combined with the main image, and when the main image is a color image, a plurality of the main images are combined. 17. The image processing apparatus according to claim 15, wherein the latent-image-embedded background image is combined with only one of the color components other than the K component among the color components of the color image. 19. The apparatus according to claim 19, further comprising a screen processing unit that performs a screen process on the latent image-embedded background image output from the selection unit or the synthesized image output from the synthesis unit with the number of output lines. The image processing apparatus according to claim 1, wherein the image processing apparatus comprises: 20. The image processing apparatus according to claim 19, wherein said screen processing means performs analog screen processing as said screen processing. 21. The image processing apparatus according to claim 19, wherein said screen processing means performs error diffusion processing as said screen processing. 22. The background image or the first and second images
22. The background image according to claim 1, wherein the background image is an image smaller than one page, and the background image or the first and second background images are used repeatedly. Image processing device. 23. The image processing apparatus according to claim 1, wherein the mask image is an image smaller than one page, and the mask image is used repeatedly. 24. Setting means for setting a gradation level of a background, wherein the background image or the first and second background images according to the gradation level set by the setting means are used. The image processing apparatus according to any one of claims 1 to 23, wherein: 25. A digital camera comprising: a first resolution converter for converting the resolution of the background image to an output resolution; and a second resolution converter for converting the resolution of the mask image to an output resolution. The image processing apparatus according to any one of claims 1 to 24, wherein: 26. The apparatus according to claim 26, further comprising: a background image storage unit configured to store the background image having a resolution lower than the output resolution; and a mask image storage unit configured to store the mask image having a resolution lower than the output resolution. The background image stored in the storage means to the first resolution conversion means,
The image processing apparatus according to claim 25, wherein the mask image stored in the mask image storage unit is output to the second resolution conversion unit. 27. A computer-readable storage medium storing a program for causing a computer to execute a process of outputting a latent image-embedded background image in which a mask image is embedded as a latent image in a background image. A halftone correction process of performing the halftone process with a rougher number of lines than the number of output lines on the background image or the background image after the grayscale correction by the grayscale correction process, A selection process of selecting a background image subjected to halftone processing in the halftone process or a background image not subjected to halftone processing in the halftone process according to the mask image and outputting a latent image embedded background image is performed. At the same time, the tone of the background image that has been subjected to halftone processing by the halftone process and the tone of the background image that has not been subjected to halftone processing by the halftone process are substantially the same at the time of output. A computer-readable storage medium storing a program for causing a computer to execute a process of performing tone correction. 28. The program according to claim 27, wherein a program for causing a computer to execute a process of performing tone correction on the background image input to the halftone dot process is stored as the tone correction process. Computer-readable storage medium. 29. The method according to claim 29, further comprising:
A program for executing a binarization process for binarizing, and inputting the output of the binarization process to the selection process as a background image that has not been subjected to the halftone process in the halftone process. Item 30. A computer-readable storage medium according to item 28. 30. As the tone correction processing, tone correction is performed on the background image, and the selection processing is input as a background image that has not been subjected to halftone processing by the halftone processing. 3. A program for performing a halftone process on the background image as a process.
A computer-readable storage medium according to claim 7. 31. A background image that has been subjected to gradation correction in the gradation correction processing is binarized by the number of output lines, and is input to the selection processing as a background image that has not been subjected to halftone processing in the halftone processing. 28. The computer-readable storage medium according to claim 27, wherein a program that executes binarization processing and performs halftone processing on the background image as the halftone processing is stored. 32. As the gradation correction processing, the gradation correction is performed on the background image and input to the halftone processing, and the gradation correction is separately performed on the background image to perform the selection processing. 28. The computer-readable storage medium according to claim 27, wherein a program to be input as a background image not subjected to halftone processing in halftone processing is stored. 33. A background image that has undergone gradation correction in the gradation correction processing is binarized by the number of output lines, and is input to the selection processing as a background image that has not been subjected to halftone processing in the halftone processing. 33. The computer-readable storage medium according to claim 32, wherein a program for executing a binarization process is stored. 34. A computer-readable storage medium storing a program for causing a computer to execute a process of outputting a latent image-embedded background image in which a mask image is embedded as a latent image in a background image, and holds the first background image. The first background image storing process to be performed and the second
Background image holding processing, halftone processing for performing halftoning processing on the second background image with a rougher number of lines than the number of output lines,
Executing a selection process of selecting either the first background image or the second background image subjected to halftone processing in the halftone process in accordance with the mask image and outputting a latent image embedded background image; A case where the same background image is subjected to the halftone process as the first background image and the second background image, and a case where the halftone process is not applied to the same background image. A computer-readable storage medium storing a program for storing an image that has been subjected to gradation correction so that gradations substantially match at the time of output. 35. A program for executing a binarization process of binarizing the first background image with the number of output lines and inputting the binarized image as the first background image to the selection process. A computer-readable storage medium according to claim 34. 36. A computer-readable storage medium storing a program for causing a computer to execute a process of outputting a latent image-embedded background image in which a mask image is embedded as a latent image in a background image, and holds the first background image. The first background image storing process to be performed and the second
Executing a background image holding process and a selecting process of selecting one of the first background image or the second background image according to the mask image and outputting a latent image embedded background image; As the background image and the second background image, the second background image is obtained by subjecting the same background image as the first background image to a halftone process with a line number coarser than the output line number. The first background image and the second
The background image of the same background image is subjected to the halftone process in the halftone process, and the grayscale is set so that the grayscale in the case of not performing the halftone process by the halftone process substantially matches at the time of output. A computer-readable storage medium storing a program for holding a corrected image. 37. The computer-readable storage medium according to claim 36, wherein a program for storing an image binarized by the number of output lines is stored as the first background image.