JPH10243222A - Image processor and image-processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a conversion method of an input image from causing inability of analysis for add-on additional information by selecting an addition method which is proper to a selected image conversion method and adding a prescribed additional information to the image signal. SOLUTION: A received image signal 901 for each color is given to an image- processing section 902, in which 1st or 2nd dither processing is selectively conducted based on a dither processing designation signal 905. After the dither processing, the processed image signal is given to a dot pattern addition section 903. A ROM 906 stores three dot sets, and the adder section 903 adds a dot pattern to the input image signal, only if a color designation signal designates a luminance signal Y and does not add any dot pattern to M, C, Bk signals. Thus, additional information applies add-on to only part of colors that are hardly perceived by human eyes. Then the image signal to which the dot pattern is subjected to add-on is given to a laser drive section, by which printing is conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and method for adding predetermined additional information to an original image signal.

[0002]

2. Description of the Related Art In recent years, image processing apparatuses such as color printers and color copiers have come to be able to form images of which terms are known by improving their performance. Under such circumstances, securities such as banknotes may be forged, and various forgery prevention techniques have been considered.

As one of the techniques, there is an add-on system in which a dot pattern indicating a machine number of an image processing apparatus is additionally printed together with a color image to be printed.

Since this dot pattern is periodically printed on the entire screen, additional information is added only to the yellow print surface.

[0005]

However, conventionally, only one of the various add-on methods described above is provided in the image processing apparatus, and the additional information is always added on by one method.

Therefore, for example, the add-on method may not be suitable for some input image conversion methods. In this case, it becomes difficult to read the added-on image and analyze the contents of the additional information.

The present invention has been made in view of the above conventional example, and has as its object to prevent a case where additional information added on by an input image conversion method cannot be analyzed.

It is another object of the present invention to add-on the additional information to an image so that the image cannot be seen by human eyes, so that the image itself can be used as an original image.

[0009]

According to an image processing apparatus of the present invention, there is provided an image processing apparatus comprising: a generator for generating an image signal;
Image converting means for selectively performing image conversion by using one of the following, generating means for generating predetermined additional information, and an image converting method used when the image converting means performs image conversion on the image signal, Selecting means for selecting an addition method for adding predetermined additional information to the image signal; and adding means for adding the predetermined additional information to the image signal by the addition method selected by the selection means. And

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) In the present embodiment, a configuration particularly in the case of an image processing apparatus using color electrophotography is shown. In the present embodiment, the input density level is M as an image signal.
(Magenta,), C (cyan), Y (yellow), BK
(Black) It is assumed that the image data is transmitted in the order of 8 bits for each color. Further, the image processing apparatus according to the present embodiment is 600 d
It is assumed that a dot pattern having a resolution of pi and indicating additional information such as a device number of the apparatus is added on only to the Y plane.

FIG. 1 shows a configuration example of a color image processing apparatus for describing the following embodiment, which is a so-called laser beam printer. First, the photosensitive drum 100 is uniformly charged to a predetermined polarity by the charger 101, and is exposed onto the photosensitive drum 100 by exposure to the laser beam L.
For example, the first latent image (magenta in the present embodiment)
Is formed. Next, in this case, a required developing bias voltage is applied only to the magenta developing device _Dm to develop a magenta latent image, and a first magenta toner image is formed on the photosensitive drum 100.

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

[0013] Next, the second latent image by the laser beam L on the photosensitive drum 100 (and cyan in this case) is formed, then the on the photosensitive drum 100 by the developing device D _c of cyan The second latent image is developed to form a second cyan toner image. Then, the transfer paper P is adjusted such that the cyan second toner image is aligned with the position of the magenta first toner image already transferred to the transfer paper P.
Is transferred to In the transfer of the second color toner image, a bias voltage of +2.1 KV is applied to the transfer drum 102 immediately before the transfer paper reaches the transfer portion.

In the same manner, third and fourth latent images of yellow and black are sequentially formed on the photosensitive drum 100, and are sequentially developed by developing units D _y and D _b , respectively.
The third and fourth toner images of yellow and black are sequentially transferred so as to be aligned with the toner image previously transferred to the transfer paper P, and thus the four color toner images are superimposed on the transfer paper P. It will be formed in the state where it was set. In this embodiment, the four colors are superimposed on the transfer paper P for the first time. However, the toner images of the four colors may be superimposed on the transfer drum and then collectively transferred onto the transfer paper P.

Next, P performed by the image processing apparatus of the present embodiment
The WM (pulse width modulation) method will be described. The PWM method is a method in which input data is converted into an analog voltage, compared with a triangular wave, converted into pulse width data, sent to a laser driver, and emits laser light for a pulse width time.

FIG. 2 is a diagram showing the principle of PWM. As described above, the image signal processed by the image processing apparatus of the present embodiment has a resolution of 600 dpi, and the triangular wave for PWM has a wavelength of 200 lines. In the drawing, the area between the dotted lines is the length of one pixel, and the vertical axis represents the analog voltage for each pixel, which corresponds to the density level from the minimum density to the maximum density. The laser is irradiated for a period of time during which the analog voltage is higher than the triangular wave, so that the toner is applied only to the laser-irradiated portion of each pixel, and that portion is printed.

On the other hand, a systematic dither method performed by the image processing unit of the image processing apparatus according to the present embodiment will be described.

FIGS. 3A and 3B are diagrams showing first and second dither matrices mounted on the image processing apparatus of the present embodiment. The number in each cell in FIG. 3 represents the threshold value in the dither matrix. The threshold value is compared with the input image signal, and if “the value of the image signal of each pixel ≧ the threshold value”, If the pixel is a black pixel, otherwise it is a white pixel.

FIG. 4 shows an example of printing a first dithered image. 4 are black pixels, and the density increases in the order of A to F in the figure. By the first dithering process, a halftone cell having a 150-line screen angle of 0 degree as shown in FIG. 4 is formed.

FIG. 5 shows a print example of an image subjected to the second dither processing, similarly to FIG. By the second dither processing, FIG.
Thus, a halftone cell having a 141-line screen angle of 45 degrees is formed. These dither processes are Y, M,
This is performed for each of the four colors C and BK.

Next, a dot pattern indicating additional information to be added on to an original image by the image processing apparatus of the present embodiment will be described. This dot pattern has a combination of ON and OFF of yellow dots called a dot set such as A, B or C in FIG. 6 as one unit, and by combining a plurality of dot sets of the same type, additional information is obtained in this positional relationship. Can be represented.
Here, the black rectangular area is a pixel for turning on the yellow dot. That is, the pixel value of yellow in the black area is replaced with yellow solid. The white rectangular area is a pixel for turning off the yellow dot. That is, the pixel value of yellow in this area is replaced with 0. The image processing apparatus according to the present embodiment can selectively use the PWM processing and the dither processing.

In this embodiment, the method of adding a dot pattern using the dot set A is selected when the first dither processing (FIG. 4) is performed. Since the halftone of the first dither has a relatively high line count of 150 lines, that is, the size of each halftone dot is small, the dot set A has a small yellow dot ON / OFF area,
The interval between the N region and OFF is set in accordance with the number of lines.
FIG. 7A shows an example in which a dot pattern using the dot set A is added on in a halftone cell of the first dither processing. This is a state when a dot pattern is added on to the image of FIG. 4C. The recognition is facilitated by hitting the ON region between the halftone cells as shown in the figure.

The pattern adding method using the dot set B in FIG. 7 is selected when the second dither processing (FIG. 5) is performed. The halftone of the second dither has a line frequency of 1
Since the width of each halftone dot is relatively low, ie, 41 lines, that is, the size of each halftone dot is large, the interval between the ON region and the OFF region is set in accordance with the number of lines so that the ON region and the OFF region of the yellow dot are also enlarged. FIG. 7B shows an example in which a dot pattern using the dot set B is added on in the halftone cell of the second dither processing. This is a state when a dot pattern is added on to the image D in FIG. Also in this case, recognition is facilitated by hitting ON regions between halftone cells as shown in the figure.

Finally, the pattern adding method using the dot set C in FIG. 7 is selected when the PWM processing is performed. FIG. 7C shows an example in which the dot set C is embedded in the 200-line PWM. The number of lines of this PEM is 200 lines,
It is the highest compared to dither 1 and dither 2. That is, since the size of each halftone dot is the smallest, the area of the yellow dot ON and OFF is made smallest, and the interval between the ON area and the OFF is set according to the number of lines. In addition, recognition is facilitated by placing an OFF area on a vertical line of the PWM as shown in the figure.

Next, a dot pattern printing method using a plurality of any one of the dot sets A or B or C will be described with reference to FIG. Reference numeral 801 denotes the above-described dot set A, B, or C, and one dot pattern 802 is formed by a combination of a plurality of the same dot sets as illustrated. The dot pattern 802 is one unit of the dot pattern.
Is repeated in the image, additional information can be obtained from any region.

An arrangement for driving the above-described dot pattern will be described. First, FIG. 9 is a block diagram showing a process of receiving an image signal and transmitting the image signal to a printing unit when performing dither processing. Since the image processing apparatus prints one screen of each color of Y, M, C, and BK as described above, the image signals are image-sequentially, that is, an image signal of one screen of M and an image signal of one screen of C. , Y, and an image signal for one screen of BK. Which color image signal is sent is designated by a color designation signal 904. That is, the color designation signal 904 is first switched in the order of C, Y, and BK every time data of one screen is designated by designating M.

The input image signal 901 of each color is 90
2 is input to the image processing unit. The image processing unit 902 selectively performs the above-described first dither or second dither processing based on the dither processing designation signal 905. The processing designation signal 905 is manually designated by, for example, a user from an operation unit of an image processing apparatus (not shown).

FIG. 10 shows a configuration for performing the first dither processing in the image processing section. First, the input 8-bit image signal 1001 is compressed to the number of dither gradations by the compression unit 1002, and is input to the comparators 1003 to 1006. At the time of this compression, density correction is also performed at the same time. On the other hand, the horizontal synchronization signal 10 representing the horizontal synchronization timing of the image signal
11 and the reference clock 1012
13 is given. The address generator 1013 generates an address based on these signals, and outputs the address to the threshold ROMs 1007 to 1010. These threshold ROMs are provided corresponding to the comparators 1003 to 1006, respectively, and store values corresponding to the thresholds in FIG. And an address generator 1013
, The threshold value stored at the address is supplied to each input terminal of the corresponding comparators 1003 to 1006. Comparators 1003 to 1006 each compare the value of the input image signal with a threshold value,
When “image signal ≧ threshold value”, a signal of an H level output is output. Otherwise, a signal of an L level output is output. The signals output from the comparators in this manner are output from selector 10
14 in parallel. The selector 1014 converts the signal applied in parallel into a serial signal and outputs it. Second
Is also performed by a similar system.

After the dither processing is performed, the image signal is input to the dot pattern adder 903 in FIG. R
The OM 906 stores the three dot sets shown in FIG. 6. When the processing specifying signal 905 specifies the first dither processing, the data shown in FIG. 6A is used. When the second dither processing is specified, the data shown in FIG. The dot pattern is loaded into the pattern addition unit 903, and the addition unit 903 adds the dot pattern to the input image signal only when the color designation signal 904 designates Y, and does not perform the addition for M, C, and BK. This makes it possible to add-on the additional information (dot pattern) only to a part of the color that is difficult for human eyes to recognize. Note that this ROM 90
The data of the three dot sets stored in No. 6 are all the same. For example, information on the machine number of the image processing apparatus is stored.

Thereafter, the image signal with the dot pattern added on is input to the laser drive unit, and printing is performed.

Next, FIG. 11 shows a block diagram of a multi-value processing unit in the image processing apparatus when performing the PWM processing. As in the case of the dither processing, the image signal 1101 is the color designation signal 110
4, M, C, Y, and K are input in this order. First, the image signal 1101 is input to the density correction unit 1102, corrected so that the relationship between the image signal and the output density becomes linear, and input to the dot pattern addition unit 1103. The ROM 1112 stores the data of the three dot sets of FIG. 6 in the same manner as described above. This time, the processing designation signal 1113 designates the dot set of FIG. 6C, and the data of FIG. The loading unit 1103 adds the dot pattern to the input image signal only when the color designation signal 1104 designates Y, and does not perform the addition for M, C, and BK.

The image signal of each color thus processed is input to a PWM (pulse width modulation) unit 1105. P
The WM unit 1105 latches the 8-bit image signal in the latch circuit 1
At 106, the voltage is synchronized with the rise of the image clock PCLK 1110, converted to an analog voltage by the D / A converter 1107, and input to the analog comparator 1108.

On the other hand, a triangular wave is generated by a triangular wave generator 1111 by the image clock 1110 and input to the analog comparator 1108. The analog voltage and the triangular wave signal are compared, and an image signal subjected to PWM processing is output from the output of the analog comparator 1108 and inverted by the inverter 1109 to obtain a PWM signal.

Although the present embodiment has been described with reference to an example of a laser beam printer, a plurality of add-on systems may be used in various other types of printers such as an ink jet printer and an LED printer in accordance with image processing of dither processing. Is applicable.

As described above, according to the present embodiment, by switching the add-on method of the additional information according to the image processing method, the additional information can be added-on by the add-on method suitable for the type of the image to be printed.

(Second Embodiment) Next, another embodiment of the present invention will be described. The image processing apparatus according to the present embodiment has a function of selectively performing the first and second dither processing in FIG. 3 as in the first embodiment.

In this embodiment, first, the position of a dither halftone cell (dither matrix) is obtained from the left margin value Lm of an image signal obtained from an externally connected host computer. 12A is a schematic diagram illustrating a first dither halftone cell, and FIG. 12B is a schematic diagram illustrating a second dither halftone cell.

The shaded areas 1201 and 1202 in the figure represent one unit of the halftone cell. These are each shown in FIG.
Corresponding to the dither matrices A and B. The left end of the image area is determined based on the left margin Lm in the figure, and thus the position of the halftone cell is also determined. In the area of the left margin Lm, since white data is output as image data, the halftone cell starts from a position advanced by Lm pixels from the left end of the sheet.

On the other hand, as the dot pattern indicating the additional information, A in FIG. 6 corresponding to the first dither processing and B in FIG. 6 corresponding to the second dither processing are stored in the ROM as in the first embodiment. Keep it. Here, in order to increase the recognition rate of the dot pattern, the positional relationship between the dot set and the halftone cell of the dither is changed as shown in FIG. 13A for the first dither processing and as shown in FIG. 13B for the second dither processing. An area 1301 where the yellow dot laser is turned on enters between the halftone dots, and the yellow dot OFF area 1301
Fix 2 so that it is above the halftone dot. To do so, in the case of the first dither processing, the position of the OFF area of the first dot set 1401 is set to the left end + 1 pixel of the halftone cell in the main scanning direction, as shown in FIG. The direction should be at the top of the halftone cell. In the case of the second dither processing, as shown in FIG. 14B, the position of the OFF area of the first dot set 1402 is set to the leftmost +2 pixels of the halftone cell in the main scanning direction and the position of the halftone cell in the sub-scanning direction. It should be at the top + 1 pixel.

In order to fix the positional relationship as described above, the position of the first dot set of the dot pattern in the main scanning direction is set to the (Lm + 1) th pixel in the case of the first dither processing, and to the Lm + 2nd pixel in the case of the second dither processing. To The position in the sub-scanning direction is the first line in the case of the first dither processing, and is the second line in the case of the second dither processing.

Next, the setting of the dot pattern size will be described. FIG. 15 is a diagram illustrating one unit of the dot pattern. 1501 represents each dot set. In the present embodiment, the sizes Lx and Ly of the dot pattern in the main scanning and sub-scanning directions are variable, and upper limits Mx and My are set in advance.

The halftone of the first dither processing has a spatial frequency of 150 lines in both the main scanning direction and the sub-scanning direction, and has a frequency of four pixel periods in terms of the number of pixels. Therefore, in order to realize the above positional relationship for each dot set, L
x and Ly are set to be the multiples of 4 and the largest values that do not exceed the upper limit values Mx and My.

Similarly, the halftone of the second dither processing has a spatial frequency of 141 lines, but has a screen angle in the direction of 45 degrees. Therefore, in order to realize the above positional relationship for each dot set, it is necessary to shift the dot set in units of 100 lines in both the main scanning direction and the sub-scanning direction. Therefore, in this case, Lx and Ly are set to be multiples of 6 and to be the largest values that do not exceed the upper limit values Mx and My.

As described above, the present embodiment has been described with respect to the case where two types of dither processing methods are used. However, if it is not determined what kind of image processing is performed by the printer controller of the image processing apparatus, the spatial frequency , The screen angle, the margin value, etc. from the printer controller, the writing position of the first dot set and L
x and Ly can be calculated and set.

In this embodiment, the writing start position of the dot set is controlled. However, the writing start position is fixed to the left end of the sheet. For example, in the case of the first dither processing, one pixel as shown in FIG. Four shifted dot sets may be held, and one of them may be selectively used depending on the left margin value.

In the first embodiment, the number of PWM processing methods is not limited to one, and a plurality of types may be selectively performed.

Further, a method for performing the operation of the image processing apparatus described above is also included in the scope of the present invention. In the case where the method is stored as a program, and the computer reads out the program and performs the above-described operation, a storage medium storing the program is also included in the scope of the present invention.

[0048]

As described above, according to the present invention, when an image signal is image-converted by selectively using one of a plurality of image conversion methods, an additional method according to the selected image conversion method is used. Thus, the predetermined additional information is added to the image signal, so that it is possible to prevent a case where the additional information added by the input image conversion method cannot be analyzed.

More specifically, when an image is converted by selectively using dither processing, PWM processing, or the like, a dot pattern of an appropriate size is added according to the number of lines of the processed image, so that the input image can be converted. Can be prevented from analyzing the additional information added-on by the conversion method.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a printing unit of an image processing apparatus described in an embodiment of the present invention.

FIG. 2 is a diagram illustrating a PWM process performed by the image processing apparatus.

FIG. 3 is a diagram illustrating a dither matrix performed by the image processing apparatus.

FIG. 4 is a diagram showing one printing example using a dither matrix.

FIG. 5 is a diagram showing one printing example using a dither matrix.

FIG. 6 is a diagram illustrating an example of a plurality of dot sets included in the image processing apparatus.

FIG. 7 is a diagram showing a state when a dot set is actually added on.

FIG. 8 is a diagram showing one unit of a dot pattern.

FIG. 9 is a block diagram illustrating a dither process and add-on of additional information;

10 is an internal configuration diagram for performing dither processing performed by the image processing apparatus of FIG. 9;

FIG. 11 is a block diagram showing a configuration for adding on a PWM process and additional information.

FIG. 12 is a schematic diagram of a halftone cell according to a second embodiment.

FIG. 13 is a diagram illustrating a state in which a dot set is added on according to the second embodiment.

FIG. 14 is a diagram showing a positional relationship between a halftone cell and a dot set according to the second embodiment.

FIG. 15 is a diagram showing a positional relationship between dot sets in a dot pattern.

FIG. 16 is a diagram showing a plurality of dot sets at different positions.

[Explanation of symbols]

 100 photosensitive drum 102 transfer drum

Claims (11)

[Claims] A generating means for generating an image signal; an image converting means for selectively converting one of a plurality of image converting methods into an image signal; a generating means for generating predetermined additional information; Selecting means for selecting an addition method for adding the predetermined additional information to the image signal, according to an image conversion method used when the image conversion means converts the image signal into an image, and selection by the selection means An image processing apparatus comprising: an adding unit that adds the predetermined additional information to the image signal by using the adding method. 2. The image processing apparatus according to claim 1, wherein the image signal is a multi-valued image signal, and the image conversion by the image conversion means converts a gradation of the multi-valued image signal. 3. The image processing apparatus according to claim 1, wherein the plurality of image conversion methods include a method of performing dither processing. 4. The apparatus according to claim 1, wherein the plurality of image conversion methods include a method of performing a PWM process. 5. The image processing apparatus according to claim 1, wherein the adding unit adds the predetermined additional information as a dot pattern. 6. The image signal is a color image signal,
2. The image processing apparatus according to claim 1, wherein the adding unit adds the additional information to a yellow component image signal included in the color image signal. 7. The image processing apparatus according to claim 1, wherein the predetermined additional information is a machine number of the image processing apparatus. 8. The content of the additional information added by the adding means is the same regardless of the image conversion method used when the image converting means converts the image signal into an image. 2. The image processing device according to 1. 9. A generating step for generating an image signal, an image converting step for selectively converting the image signal using one of a plurality of image converting methods, and a generating step for generating predetermined additional information. A selection step of selecting an addition method for adding the predetermined additional information to the image signal according to an image conversion method used when the image conversion step converts the image signal into an image; An image processing method, further comprising an adding step of adding the predetermined additional information to the image signal by the added adding method. 10. A halftone processing means for generating an image signal, performing halftone processing on the image signal by selectively using one of a plurality of halftone processing methods, and generating predetermined additional information. Generating means for adding the predetermined additional information to the image signal based on a spatial frequency of a halftone cell corresponding to the halftone processing method selected by the halftone processing means and a writing position of the image signal; And an image processing apparatus. 11. A halftone processing step of generating an image signal and performing halftone processing on the image signal by selectively using one of a plurality of halftone processing methods, and generating predetermined additional information. Generating, and adding the predetermined additional information to the image signal based on a spatial frequency of a halftone cell corresponding to the halftone processing method selected in the halftone processing step and a writing position of the image signal. And an image processing method.