JP3728052B2 - Image processing apparatus and method, and storage medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus and method having a function of adding additional information to an input image, and a storage medium.
[0002]
[Prior art]
In recent years, image recording apparatuses such as color printers and color copiers have been able to form high-quality images due to improved performance. Under such circumstances, securities such as banknotes may be forged, and various anti-counterfeit technologies have been considered.
[0003]
As one of the techniques, there is an additional method in which a dot pattern indicating additional information such as a machine number of the image processing apparatus is additionally printed together with a color image to be printed.
[0004]
Further, since this dot pattern is periodically printed on the entire screen, additional information is added only to the yellow printing surface.
[0005]
In recent years, various types of halftone processing such as dithering and error diffusion methods have been selectively executed in order to save the amount of data handled by the host computer or printer or to print a high-quality halftone image on the printer. To be done.
[0006]
[Problems to be solved by the invention]
When a plurality of halftone processes are selectively executed as described above, the compatibility between a certain halftone process and the shape of the dot pattern is good, but the compatibility between a certain halftone process and the shape of the dot pattern is good. There is a problem of getting worse.
[0007]
In other words, if the compatibility is poor, an image printed using the halftone processing may cause the dot pattern to be noticeable, resulting in a substantial deterioration in image quality, or additional information embedded from the printed image. There was a problem that it was difficult to decipher.
[0008]
In order to cope with such a problem, it is conceivable to provide an image processing apparatus provided with each dot pattern generation method suitable for each halftone processing. However, the cost of the apparatus is increased by having a plurality of dot pattern generation methods. There is a problem that will rise. In addition, although any of the dot patterns having a plurality of shapes is added to the image in spite of showing the same additional information, there is a problem that it takes time to decode the printed image.
[0009]
The present invention has been made in view of the above problems, and an object thereof is to provide a single dot pattern addition method suitable for any of a plurality of halftone processes that can be selectively performed.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, an image processing apparatus according to the present invention includes an input unit that inputs an image signal,
The image signal inputted by said input means, and halftone processing means for halftone processing by executing a plurality of halftone processing method selectively,
Have on the halftone processed image signal, and adding means for adding hard to identify the dot pattern to the human eye showing the additional information by the halftone processing unit,
The dot pattern is composed of a first region and a plurality of second regions, each having a different longitudinal direction, and the size of each of the first region and the plurality of second regions is selected from any of the plurality of halftone processing methods. However, it is set so that it can be recognized .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
In the present embodiment, the configuration of an image recording apparatus using color electrophotographic technology is shown.
[0012]
The image recording apparatus of the present embodiment can print at a resolution of 600 dpi. In the present embodiment, image signals input from an external computer or the like are sent in frame sequential order in M (magenta), C (cyan), Y (yellow), and BK (black). The signal density level is expressed by 8 bits. A recognition signal added to these image signals is called an add-on dot. In the present embodiment, the recognition signal is added only to the Y (yellow) image signal. This is based on the fact that among the above colors, the yellow image is most difficult to be identified by human eyes. As a result, even if a recognition signal is added and printing is performed, it is not necessary to substantially deteriorate the image quality from the original image.
[0013]
FIG. 1 shows a color image recording apparatus used in each embodiment of the present invention.
[0014]
First, the charging drum 101 uniformly charges the photosensitive drum 100 to a predetermined polarity, and a magenta first latent image, for example, is formed on the photosensitive drum 100 by exposure with the laser beam L. Next, in this case, a required developing bias voltage is applied only to the magenta developing device Dm to develop the magenta latent image, and a magenta first toner image is formed on the photosensitive drum 100.
[0015]
On the other hand, the transfer paper P is fed at a predetermined timing, and immediately before the leading edge reaches the transfer start position, a transfer bias voltage (+1.8 KV) having a polarity opposite to that of the toner (for example, plus polarity) is applied to the transfer drum 102. Then, 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 to prepare for the next color latent image formation and development process.
[0016]
Next, a second cyan latent image is formed on the photosensitive drum 100 by the laser beam L, and then the second latent image on the photosensitive drum 100 is developed by the cyan developing device Dc. The second toner image is formed. The cyan second toner image is transferred onto the transfer paper P in accordance with the position of the first magenta toner image transferred onto the transfer paper P. In transferring 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.
[0017]
Similarly, the yellow and black third and fourth latent images are sequentially formed on the photosensitive drum 100, and are sequentially developed by the developing devices Dy and Db, respectively, and transferred to the transfer paper P in advance. The third and fourth toner images of yellow and black are sequentially transferred in alignment with the image, and thus the four-color toner images are formed on the transfer paper P in an overlapping state.
[0018]
FIG. 2 is a diagram illustrating a flow of signal processing according to the first embodiment.
[0019]
In FIG. 2, the host 201, the controller 202, and the engine 203 have independent main control units (CPUs) for controlling each block in each device. That is, the host 201 has a CPU 2010, the controller 202 has a CPU 2020, and the engine 202 has a CPU 2030. Each CPU controls the operation timing in each machine and communication between each device via a bus (not shown). ing.
[0020]
In general, in general, an image processing apparatus such as a laser beam printer used in the present embodiment often includes a controller unit and an engine unit separately. For this reason, it is usually configured such that each device is closed so that each device is individually controlled.
[0021]
RGB image signals are sent in parallel from the host 201 and input to the controller 202. In addition, the host 201 can instruct the selection of three types of halftone processing: dither 1, dither 2, and superpixel, and the user selects one of the predetermined operations on the host 201 at the time of printing. The halftone number thus transmitted is sent to the controller 202 as a halftone instruction signal.
[0022]
In the present embodiment, a halftone instruction signal is input to the controller 202 through a signal line dedicated to a control signal that is different from the dedicated line for image signals. As a result, signals can be exchanged independently of transmission / reception of image signals, and the degree of freedom of signal transmission / reception timing is increased.
[0023]
The present invention is not limited to this, and a halftone instruction signal may be input as a parallel command through the same data line as the image signal.
[0024]
In the controller 202, a CPU 2020, a color conversion processing unit 204, a γ correction unit 205, and a halftone processing unit 206 are arranged. The input RGB signal is subjected to masking and UCR processing by the color conversion processing unit 204, color correction and under color removal are performed, and magenta (M), cyan (C), yellow (Y), black (BK) ) Image signal.
[0025]
As described above, the image recording apparatus prints one screen for each of the colors Y, M, C, and BK (in the surface sequence). Image signals are output in the order of data for one screen, data for one screen of Y, and data for one screen of BK.
[0026]
Next, correction is performed by the γ correction unit 205 so that the output density curve becomes linear, and the correction is input to the halftone processing unit 206.
[0027]
On the other hand, a halftone instruction signal is input to the halftone processing unit 206 in parallel with this. A halftone processing unit 206 processes image data input in accordance with a halftone instruction signal. When dither 1 and dither 2 are instructed, predetermined multi-value dither processing is performed. These dither processes will be described in detail later. Further, when a super pixel to be described later is designated, the dither process is not performed.
[0028]
After the above processing is performed by the controller 202, M, C, Y, and BK image signals are input to the engine 203.
[0029]
The engine 203 includes a CPU 2030, an add-on addition processing unit 207, a PWM processing unit 208, and a laser driving unit 209. An add-on pattern is added by the add-on addition processing unit 207 only when the input image signal is yellow. Thereafter, the PWM processor 208 applies pulse width modulation.
[0030]
The halftone instruction signal described above is input to the engine 203 by a serial command or the like at the same time as being input to the halftone processing unit 206, and is input to the PWM processing unit 208.
[0031]
The PWM processing unit 208 performs known PWM processing in units of 600 lines when dither 1 or dither 2 is instructed in accordance with the input halftone instruction signal, and is modulated in units of 200 lines when super pixels are instructed. The PWM signal is input to the laser drive unit 209 and printed.
[0032]
Next, the operation of the add-on addition processing unit 207 will be described.
[0033]
FIG. 4 is an internal block diagram of the add-on addition processing unit 207. The operation of the block will be briefly described below. The CPU 2030 reads additional information such as an engine ID stored in the EEPROM 401 and outputs it to the encryption circuit 405. The encryption circuit 405 encrypts this additional information. Next, the parity of the encrypted additional information is checked by the parity check 406, and if there is an error, the printing operation is stopped.
[0034]
The main scanning counter 407 performs a counting operation according to the clock signal PCLK in the main scanning direction of the image signal, and sends ON at a position where an add-on dot should be added according to the code loaded from the parity check 406.
[0035]
The sub-scanning counter 408 performs a counting operation according to the clock signal BD in the sub-scanning direction, and sends ON on-line. The add-on dot generation circuit 409 receives an add-on dot shape parameter stored in the ROM 403 in the CPU 2030, and when the add-on permission signal that is ON only when processing the yellow image signal is ON, and the main scanning counter 407, Only when both the sub-scanning counters 408 are ON, an add-on dot is generated and transmitted with BK in the FF area and WH in the 00 area.
[0036]
The add-on addition circuit 404 converts the image signal to FFh when the BK is ON with respect to the yellow image signal input from the controller 202 and outputs it to the PWM processing unit 208 when the WH is ON and 00h when the WH is ON. If both BK and WH are OFF, the input image signal is output to the PWM processing unit 208 as it is.
[0037]
The state of the image to which the additional information is added by the above process will be described later.
[0038]
Next, the operation of the PWM processing unit 208 will be described.
[0039]
FIG. 3 is a block diagram of the PWM processing unit 208. The image signal input from the add-on addition circuit 404 is synchronized with the rising edge of the image clock PCLK by the latch circuit 301, converted to an analog voltage by the D / A converter 302, and input to the analog comparator 303.
[0040]
On the other hand, a triangular wave generation unit 306 generates a 600-line triangular wave by an image clock, and at the same time, a triangular wave generation unit 307 generates a 200-line triangular wave by passing through the 1/3 frequency divider 305.
[0041]
Here, the line number changeover switch 308 is switched by a halftone instruction signal, and selects a 600-line triangular wave when instructing dither 1 and dither 2, and a 200-line triangular wave when instructing a super pixel.
[0042]
The analog voltage and the two signals of the triangular wave are compared, and a PWM signal is output from the output of the analog comparator 303 and is inverted by the inverter 304 to obtain a PWM signal.
[0043]
Here, the principle of PWM performed by the PWM processing unit 208 will be briefly described.
[0044]
FIGS. 7A and 7B are views showing the state of PWM processing of 600 lines and 200 lines, respectively. The width between the dotted lines in the figure is the width of one pixel, and the vertical axis represents the analog voltage for each pixel, corresponding to the density levels of the minimum density to the maximum density. The laser (corresponding to the laser beam L in FIG. 1) is irradiated for a time during which the analog voltage 701 is higher than the triangular wave 702, so that the toner is placed only on the laser irradiated portion 703 of each pixel and the portion is printed. The
[0045]
In the case of 600 lines in FIG. 5A, the irradiation area changes in units of one pixel to express gradation. On the other hand, in the case of line 200 in FIG. 5B, gradation is expressed in units of three pixels.
[0046]
Next, dither 1 and dither 2 that can be executed by the halftone processing unit 206 of the present embodiment will be described.
[0047]
5A and 5B are diagrams showing halftone cells of dither 1 and dither 2. FIG. Reference numeral 501 denotes a halftone cell of dither 1, which has a screen angle of 45 degrees and a dot number (spatial frequency) of 141 lines / inch, and grows in a spiral shape from the center in a fattening type in each cell.
[0048]
Reference numeral 502 denotes a dither 2 halftone cell having a screen angle of 0 degrees and a number of dotted lines of 150 lines / inch, and vertically grows vertically from the center in each cell.
[0049]
Each pixel has a depth of, for example, 4 gradations, and the gradation of each pixel is expressed by 600 line PWM. As a result, halftone dots in a yellow density region of about 25%, which is often found in banknotes and the like, have shapes as shown in FIGS. 6A and 6B, respectively.
[0050]
When the super pixel mode is selected, 200-line PWM processing is performed, so that the halftone dots in the region having a yellow density of about 25% have a shape as shown in FIG.
[0051]
When an add-on dot is added to an image that has been subjected to each halftone process having the above characteristics, the positional relationship between the halftone dot and the add-on dot greatly affects the difficulty of decoding or the conspicuousness.
[0052]
Further, since the positional relationship between the halftone dots and the add-on dots is arbitrarily changed by the user changing the margin, it cannot be controlled by the printing apparatus (engine 203). Therefore, it is necessary to determine the optimum shape of the add-on dot in consideration of the positional relationship in which the add-on dot is hardly recognized from the formed image and the positional relationship in which the add-on dot is most noticeable in the formed image.
[0053]
FIG. 8 shows an example of the shape of a conventional add-on dot. A dotted line in the figure represents an add-on line and is a line to which each add-on dot should be added. Reference numeral 804 denotes each add-on dot.
[0054]
Further, 805 is an enlargement of the add-on dot 804. In the add-on dot 805, the area corresponding to the FF area 801 is replaced with the original input image with the highest density (only for the yellow surface image), and the areas corresponding to the 00 areas 802 and 803 have the original input image with the lowest density. (Only for the yellow side image). That is, the pixels in the FF area are converted into FFh, and the pixels in the 00 area are converted into 00h. Note that the pixels in the hatched area are not modulated. This add-on dot is repeatedly added to the image.
[0055]
Further, the additional information is expressed by a combination of these plural add-on dots. For example, several bits of information can be expressed by the distance between add-on dots adjacent vertically or horizontally.
[0056]
FIG. 9 shows an example in which the conventional add-on dot is added to each halftone dot shown in FIG. FIGS. 9A, 9B, and 9C show results of printing an image signal by performing dither 1, dither 2, and superpixel, respectively.
[0057]
As for FIG. 9A, the 00 area 90 on both sides overlaps with the white background of the original image, so this area cannot be decoded and recognized from the printed image. Further, although one pixel protrudes from the dither halftone dot in the FF area 91, it is impossible to decode and recognize that it is the FF area with only one pixel.
[0058]
In FIG. 9B, both the FF area and the 00 area overlap with the original image, and cannot be decoded or recognized at all from the printed image.
[0059]
In FIG. 9C, the 00 area replaces the original data with white for all three pixels, so that the 00 area can be decoded and recognized from the printed image. It stands out clearly. From the above, the conventional add-on dot shape is insufficient in both recognition and conspicuousness.
[0060]
Particularly in the electrophotographic system, since at least about 2 pixels do not protrude from the halftone dot, it cannot be recognized as a dot. Therefore, in order to be able to be surely recognized even in the case of FIG. is necessary. However, if the FF region has an area of 5 pixels or more in the vertical direction, it will be noticeable on a white background. Therefore, the FF region is changed to one having a vertical size of 4 pixels.
[0061]
On the other hand, even if this FF area overlaps the vertical line of the halftone dots in FIGS. 6B and 6C, the functions of the 00 areas on both sides are important in order to recognize the add-on dots.
[0062]
First, in FIG. 6B, in order to recognize the outline, it is necessary that the 00 area is present at a position away from the FF area by 4 pixels in the main scanning direction.
[0063]
In addition, unlike (B) in the figure, in (C) in the figure, 00 area is required at a position 3 pixels away from the FF area in the main scanning direction in order to recognize the outline.
[0064]
Further, the white outline on the vertical line is not sufficiently recognized by one pixel, and conversely, the deterioration of the image becomes conspicuous if three pixels are used. Therefore, it is determined by 2 pixels. In order to increase the decoding and recognition rate, the 00 area is arranged on both sides of the FF area. However, if there are two pixels on both sides, the 00 area is one pixel wide.
[0065]
Considering the above, FIG. 10 shows the generated add-on dot pattern of the present embodiment. The FF area 1001 has a size of 1 × 4, and for the 00 areas on both sides, the 00 area 1002 has a size of 3 × 1, and the 00 area 1003 has a size of 3 × 2. Note that the hatched area does not modulate the input image.
[0066]
FIG. 11 shows an example in which this add-on dot is added to each halftone dot in FIG. 6 in the position relationship that is most difficult to decipher, that is, an example in which the add-on dot and halftone dot are in the worst position.
[0067]
In FIG. 11A, the 00 regions 110 and 111 on both sides cannot be recognized because they overlap with the white background of the original input image, but the FF region 112 can be decoded and recognized because two pixels protrude from the halftone dots of the dither. .
[0068]
In FIG. 11B, the FF area 112 cannot be recognized because it overlaps with the halftone dots, but the 00 areas 110 and 111 on both sides can be recognized as the breaks of the halftone dots.
[0069]
In FIG. 11C, the 00 area on both sides can be recognized as a halftone dot break as in FIG. 11B.
[0070]
Further, since the 00 area 111 is 2 pixels wide and the 00 area 110 is 1 pixel wide and the vertical lines are replaced with white lines, it is possible to form an image with substantially no deterioration in image quality.
[0071]
As described above, by using the add-on dots of the present embodiment described in FIG. 10, even when a plurality of halftone processes are selectively performed, additional information can be easily decoded and recognized from a printed image. In addition, it is possible to form an image without substantial deterioration in image quality.
[0072]
By reading a dot pattern representing additional information added to the original image input as described above with an image scanner or the like and extracting only the yellow plane, additional information indicating the machine number of the recording apparatus can be obtained. it can. Therefore, it is possible to determine the state of image formation from this additional information.
[0073]
As described above, the present embodiment has been described by taking the laser printer as an example, but it is needless to say that the present invention can also be applied to other various types of printers such as an inkjet printer and an LED printer.
[0074]
Further, in the present embodiment, an add-on dot that can be applied to three types of halftone processing is shown, but it is needless to say that this add-on dot can also be applied to other typical halftone processing.
[0075]
For this reason, halftone processing is performed by the controller 202 in the present embodiment, but cases where various types of halftone processing are selectively performed on the host computer 201 are also included in the present invention. That is, a single add-on pattern can be added regardless of which of the multiple types of halftone processing performed by the host computer is executed.
[0076]
Even when a plurality of controllers that perform different halftone processes are connected to the engine 203, if the add-on pattern of the present embodiment is similarly prepared in the engine 203, it can be easily performed from a printed image. The additional information can be decoded and recognized, and an image without substantial image quality deterioration can be formed.
[0077]
As described above, according to the present embodiment, even when a plurality of halftone processes are selectively performed, the additional information is always added using a single add-on dot pattern, thereby reducing the cost of the apparatus. be able to.
[0078]
Furthermore, when adding the same additional information, always using an add-on dot pattern of the same shape, compared to changing the shape of the add-on dot pattern by using a plurality of halftone processes. When the print image is decoded and additional information is obtained, it is possible to avoid obtaining incorrect information.
[0079]
Even if the present invention is applied as a part of a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus composed of a single device (for example, a copying machine, a facsimile machine). You may apply to one part of.
[0080]
In addition, the present invention is not limited only to the apparatus and method for realizing the above-described embodiment, and software for realizing the above-described embodiment on a computer (CPU or MPU) in the system or apparatus. A case in which the above-described embodiment is realized by supplying a software program code and causing the system or apparatus computer to operate the various devices according to the program code is also included in the scope of the present invention.
[0081]
In this case, the program code of the software itself realizes the function of the above embodiment, and the program code itself and means for supplying the program code to the computer, specifically, the program code Is included in the scope of the present invention.
[0082]
As a storage medium for storing such a program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.
[0083]
Further, the computer controls various devices according to only the supplied program code, so that not only the functions of the above embodiments are realized, but also the OS (operating system) on which the program code is running on the computer. Such program code is also included in the scope of the present invention when the above embodiment is realized in cooperation with a system) or other application software.
[0084]
Further, after the supplied program code is stored in the memory of the function expansion board of the computer or the function expansion unit connected to the computer, the program code is stored in the function expansion board or function storage unit based on the instruction of the program code. The case where the CPU or the like provided performs part or all of the actual processing and the above-described embodiment is realized by the processing is also included in the scope of the present invention.
[0085]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a single dot pattern addition method suitable for any of a plurality of halftone processes that can be selectively performed. Since there is no need to switch the dot pattern addition method, additional information can be added with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a printing unit of a color image recording apparatus. FIG. 2 is a diagram showing a flow of signal processing. FIG. 3 is a block diagram of a PWM processing unit. 5 is a diagram showing a halftone cell of dither processing. FIG. 6 is a diagram showing a print example of halftone processing. FIG. 7 is a diagram showing the principle of PWM. FIG. 8 is a diagram showing an add-on dot of a conventional example. Example of adding conventional add-on dots to each halftone dot [Fig. 10] Diagram showing add-on dots [Fig. 11] Example of adding add-on dots to each halftone dot [Explanation of symbols]
100 Photosensitive drum 101 Charger 102 Transfer drum 103 Cleaner 201 Host 202 Controller 203 Engine 207 Add-on addition processing unit 804 Add-on dot

Claims (9)

Input means for inputting image signals;
The image signal inputted by said input means, and halftone processing means for halftone processing by executing a plurality of halftone processing method selectively,
Have on the halftone processed image signal, and adding means for adding hard to identify the dot pattern to the human eye showing the additional information by the halftone processing unit,
The dot pattern is composed of a first region and a plurality of second regions, each having a different longitudinal direction, and the size of each of the first region and the plurality of second regions is selected from any of the plurality of halftone processing methods. An image processing apparatus that is set so as to be recognizable . The image processing apparatus according to claim 1 , wherein the halftone processing method is a dither processing method.   The image processing apparatus according to claim 1, wherein each of the first area and the second area includes a plurality of pixels. The first area is a print area when an image indicated by an image signal to which a dot pattern is added by the adding means is printed, and the second area is an image signal to which a dot pattern is added by the adding means. The image processing apparatus according to claim 1, wherein the image processing apparatus is a non-printing area when the image indicated by is printed. The image processing apparatus according to claim 1, wherein the plurality of second regions have different shapes.   The image processing apparatus according to claim 1, wherein the additional information is information representing a machine number of the image processing apparatus. 2. The image signal input by the input means is a color image signal composed of a plurality of colors, and the additional information adds a dot pattern only to a yellow color image signal. Image processing device. An input process for inputting to the image signal;
A halftone processing step of selectively executing a plurality of halftone processing methods on the image signal input in the input step,
Wherein the halftone process with respect to the halftone processed image signal, and a addition step of adding hard to identify the dot pattern to the human eye showing the additional information,
The dot pattern is composed of a first region and a plurality of second regions, each having a different longitudinal direction, and the size of each of the first region and the plurality of second regions is selected from any of the plurality of halftone processing methods. An image processing method, wherein the image processing method is set so that it can be recognized . An input process for inputting to the image signal;
A halftone processing step of selectively executing a plurality of halftone processing methods on the image signal input in the input step,
Wherein the halftone process with respect to the halftone processed image signal, and a addition step of adding hard to identify the dot pattern to the human eye showing the additional information,
The dot pattern is composed of a first region and a plurality of second regions, each having a different longitudinal direction, and the size of each of the first region and the plurality of second regions is selected from any of the plurality of halftone processing methods. A storage medium storing a control program which is set so as to be recognizable even if it is readable from a computer.

Images