JP4503913B2 - Printing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a printing method for printing a printed matter with improved anti-counterfeiting, for example, printing a high-quality face image or personal image such as characters for personal authentication of ID cards such as a license.
[0002]
[Prior art]
Recently, various security technologies have been applied to image display bodies containing face images for personal authentication such as licenses, credit cards, and membership cards. For example, it is known that a hologram film disclosed in Japanese Patent No. 2840825 is formed on an image display body to prevent copying.
[0003]
In addition, a license that attempts to authenticate an individual by printing a face image is also known as a security technology.
In addition to normal face images, face images printed with a reduced density of face images (hereinafter referred to as ghost images) are printed side by side with normal face images to improve security. Is also known.
[0004]
On the other hand, with the digitization of information and the spread of the Internet, techniques such as digital watermarks and digital signatures have become important. Such a technique is effective in measures against illegal copying, counterfeiting, and tampering, for example, when a photograph in which copyright information is embedded is distributed on the Internet.
[0005]
Such a technique is disclosed not only for electronic information but also for a printed matter. For example, Japanese Patent Laid-Open No. 2001-274971 discloses a digital watermark technique for embedding an image in a print image for printing. According to this technique, the embedded image is not only hardly perceived by humans, but the embedded image can be restored even after the image is printed.
[0006]
[Problems to be solved by the invention]
However, printed matter using the above technique has the following problems.
Ghost images are printed with the face image density reduced, and if there is a printing device that can print face images, the ghost image can be printed just by processing the image data, and security is improved. There is a problem that it is low.
[0007]
Also, the digital watermark technology that embeds an image in a printed matter is difficult for humans to perceive a high-resolution image, but for example, in an image having a resolution of 400 dpi or less, the embedded image is easily perceived by humans. There is.
Furthermore, the digital watermark technology that embeds an image in a printed material is not applicable to all recording methods, and the melt type thermal transfer recording method described later has a problem that the embedded image is easily perceived by humans. In addition, in the recording method in which the actual resolution of the image is lowered, there is a problem that the embedded image is easily perceived by humans.
Moreover, when it becomes easy to be perceived by humans as described above, if the perceived image is in an image for authenticating an individual such as a face image, it not only causes noise but also inhibits personal authentication. There is a problem that there is a possibility.
[0008]
In order to enhance the security of printed matter, a protective layer having an optical security pattern layer such as a hologram pattern is often provided on the image. If the security pattern is present on the embedded image, for example, the printed matter There is a problem that it becomes difficult to restore the embedded image when determining whether the image is true or false.
[0009]
Therefore, an object of the present invention is to provide a printing method that can ensure high security.
[0010]
[Means for Solving the Problems]
The printing method of the present invention is a printing method for printing a face image that is a multi-valued image, a ghost image that is a face image with a reduced density of the face image, and a binary image such as a character on a print medium. In the case of binary images such as face images, ghost images, and characters, which are multi-valued images, even-numbered pixels and odd-numbered pixels are alternately formed for each recording line when a multi-valued image is recorded. Thus, when recording the binary image, the recording pixels are arranged in a staggered pattern, and the even-numbered pixels and the odd-numbered pixels are arrayed as recording pixels in all the recording lines, and a plurality of heating elements are arranged in a line shape. Printing using a thermal transfer recording system that performs thermal transfer recording using a thermal head arranged in the above, and the ghost image is binary image data related to an image printed on the print medium. With performing predetermined processing with respect to the value image data, the recording pixel positions which are arranged in the staggered manner, the inclined 45 degrees with respect to the recording line direction, embedded in concentrations lower face image of the face image printing It is characterized by doing.
[0011]
The printing method of the present invention also prints a face image that is a multi-valued image, a ghost image that is a face image with a reduced density of the face image, and a binary image such as a character on a print medium. In the method, the multi-valued image such as a face image, a ghost image, and a binary image such as a character, when recording a multi-valued image, alternately even-numbered pixels and odd-numbered pixels for each recording line. By forming the recording pixels in a zigzag pattern and recording a binary image, the even-numbered pixels and the odd-numbered pixels are arranged as recording pixels in all the recording lines, and a plurality of heating elements are arranged. Printing is performed using a thermal transfer recording system that performs thermal transfer recording using a thermal head arranged in a line, and the ghost image is binary image data related to an image printed on the print medium. With performing predetermined processing with respect to the binary image data, in the recording pixel positions which are arranged in the staggered manner, the inclined 45 degrees with respect to the recording line direction, embedded in concentration lower face image of the face image Quantization processing is performed for each pixel on the image data in which the binary image data is embedded, and the quantized pixel is determined from a range of peripheral pixels for diffusing a preset quantization error and a diffusion coefficient for each peripheral pixel. The image data obtained by performing error diffusion processing on the peripheral pixels is printed.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows the configuration of a printed material according to the first embodiment. The printed material 1 is printed on a print medium such as paper, for example, a human face image 2 which is a multi-valued color image, a ghost image 3 which is a face image in which the density of the face image 2 is reduced, and characters as a binary image. 4 and a predetermined pattern 5 (star mark in the figure) are printed.
The ghost image 3 is printed by embedding a binary image 6 related to the image printed on the printed matter 1 so that it is difficult for humans to perceive it. In the present embodiment, the pattern (star symbol) 5 is embedded in the ghost image 3 as a binary image 6.
[0013]
A hologram pattern 7 as an optical security pattern is formed on the image printed on the printed matter 1. In this case, the hologram pattern 7 is patterned so as not to exist in the face portion of the ghost image 3 in which the binary image 6 is embedded.
[0014]
FIG. 2 is a flowchart showing a processing procedure for printing the face image 2 and the ghost image 3 according to the first embodiment, which will be described below.
First, for example, a color face image of a person obtained from a scanner or a digital camera is taken in (step S1), and the image data is processed. That is, a normal face image is obtained by first converting red (R), green (G), and blue (B) signals to yellow (Y), magenta (M), cyan (C), or Y, M, C, and black (K). ) Is converted (step S2), and then image processing such as edge enhancement and brightness correction is performed (step S3). Next, a recording signal conversion process for converting the recording signal to drive the printer is performed (step S4), and then a face image recording signal is sent to a printer (not shown).
[0015]
A printer (not shown) is, for example, a printer that performs printing using a thermal transfer recording method that performs thermal transfer recording using a line-type thermal head in which a plurality of heating elements are arranged in a line.
[0016]
On the other hand, ghost images are processed as follows. That is, first, a reduction process for reducing the image is performed on the face image obtained in step S1 (step S5), and then a density reduction process for processing the image density to be ½ or less of the normal density. (Step S6).
[0017]
Next, the binary image data of the pattern 5 prepared in advance is embedded in the ghost image data obtained in step S6, and the image data embedded with the binary image data is transferred to the color conversion process in step S2. Send (step S7). In the subsequent processing, the same processing as the face image described above is performed, and a ghost image recording signal is sent to the printer.
[0018]
Through the processing described above, the face image 2 and the ghost image 3 are printed on the print medium. Here, the ghost image 3 is a face image with a low density, and the ghost image 3 itself is hardly perceived by humans, and noise in the image is also difficult for humans to perceive. Moreover, since the binary image 6 embedded in the ghost image 3 is also relatively thin, it is difficult for humans to perceive it. Further, the existence of the ghost image 3 is significant, and the individual is not authenticated by the image.
[0019]
From the above, even if it is a print image by a printer with a low resolution, noise due to embedding the binary image 6 becomes difficult to perceive, and security can be improved. Further, in the present embodiment, since the binary image 6 is embedded in the ghost image 3, it is difficult to falsify and security can be further improved as compared with the case where only the ghost image 3 is printed.
[0020]
Next, the alternate driving of the heating elements of the thermal head in the printer according to the present invention, more specifically, a fusion type thermal transfer recording system in which transfer dots are arranged in a staggered pattern will be described.
[0021]
In the melt-type thermal transfer recording method in which an image is formed with or without dots, when a multi-tone image is expressed, density modulation is performed by changing the area of the dots. For this reason, it is required to accurately modulate the dot size. In order to accurately modulate the dot size, it is desirable to perform heating element alternating drive of the thermal head described later.
[0022]
The alternate driving of the heating elements of the thermal head is a method of alternately driving odd-numbered heating elements of odd lines and even-numbered heating elements of even lines for each recording line. When alternately driven in this way, the recorded dots 8 are arranged in a staggered manner to form an image as shown in FIG. Here, the main scanning direction is the direction in which the heat generating elements of the thermal head are arranged, and the sub-scanning direction is a direction orthogonal (crossing) to it.
[0023]
FIG. 4 shows the temperature distribution in the ink layer of the thermal head heating element and the thermal transfer ink ribbon, and reference numeral 9 in the figure denotes the thermal head heating element. When recording is performed by driving all the heating elements 9 instead of alternating driving, as shown in FIG. 4A, the distance between the adjacent heating elements 9 is narrow, causing thermal interference and a flat temperature distribution. (A solid line a in the figure). That is, there is no temperature contrast between adjacent heating elements 9. For this reason, accurate dot size modulation cannot be performed, and multi-tone recording becomes difficult.
[0024]
On the other hand, as shown in FIG. 4B, in the case of alternate driving in which the adjacent heating elements 9 are not driven for each recording line, the distance between the driven heating elements 9 is large (more specifically, the heating element arrangement pitch). Since the heat escapes to the heating element 9 that is not driven in the thermal head, there is almost no thermal interference, and the temperature distribution has a steep shape (solid line b in the figure). That is, a temperature contrast can be obtained between the adjacent heating elements 9.
[0025]
In this way, by alternately driving the heating elements, it is possible to reliably form isolated dots, and furthermore, the dot size can be reliably modulated without being affected by adjacent dots, and area gradation is utilized. Multi-tone recording becomes possible.
[0026]
When the printed matter 1 as shown in FIG. 1 is printed by the above-described melt type thermal transfer recording method, multi-valued images such as the face image 2 and the ghost image 3 are gradation-recorded by alternately driving the heating elements, and the characters are recorded. For binary images such as 4 and 5, the heating elements are not driven alternately, and dots are arranged in a line in both the main scanning direction and the sub-scanning direction to form an image. The processing for printing the face image 2 and the ghost image 3 is the same as that in FIG. 2 and will not be described in detail. However, in the image processing in step S3, processing for rearranging the pixel data so as to form a staggered arrangement is added.
[0027]
When the binary image 6 is embedded in the ghost image 3 printed using the alternating drive of the heating elements, for example, since the odd dots of the even lines do not exist, the embedded binary image 6 is lost every other pixel. However, since the binary image 6 such as a pattern is embedded, the shape can be secured when restored, and there is no hindrance to authenticity determination or the like. Moreover, since it is embedded in the ghost image 3, security can be improved for the same reason as described above.
[0028]
FIG. 5 schematically shows the configuration of a printed material according to the second embodiment. Since the printed image 1 has the same face image 2, character 4, pattern 5, hologram pattern 7 and the like as the first embodiment (FIG. 1) described above, the description is omitted, but the ghost image 3 has a binary value. The image 6 is different from the first embodiment in that the image 6 is embedded and printed at a certain angle. In the drawing, for example, the case of an example in which the binary image 6 is embedded at an angle of 45 degrees is shown.
[0029]
As described above, in the melt-type thermal transfer recording method, the multi-value image expresses gradation by alternately driving the heating elements of the thermal head. The dot arrangement is as shown in FIG. Looking at the AA line in FIG. 6, the dots are not arranged every other dot, but are arranged in a line at a certain pitch (specifically, 1 / √2 of the pitch of the heating element). This angle depends on the driving method, but typical examples are shown in FIGS.
[0030]
FIG. 7 shows a case where the interval between the even lines and the odd lines is the same as the pitch of the heating elements of the thermal head. In this case, the direction in which the dots are arranged in a line is an angle of 45 degrees from the main scanning direction (lateral direction in the figure).
FIG. 8 shows a case where the interval between the even-numbered lines and the odd-numbered lines is ½ of the pitch of the heat generating elements of the thermal head. In this case, the direction in which the dots are arranged in a line is an angle of about 26.565 degrees from the main scanning direction (lateral direction in the figure).
When embedding the binary image 6 in the ghost image 3, if it is embedded at an angle as described above, the pixel data of the embedded binary image 6 will not be lost even if alternate driving is performed.
[0031]
FIG. 9 is a flowchart showing a processing procedure for printing the face image 2 and the ghost image 3 according to the second embodiment, which will be described below.
Since the face image processing is the same as the processing in FIG. 2 (steps S1 to S4), description thereof is omitted. However, in the image processing in step S3, processing for rearranging pixel data only in the face image in a staggered arrangement is added.
[0032]
Since the processing related to the ghost image is the same as the processing in FIG. 2 (steps S1 to S7, S2 to S3), the reduction processing, density reduction processing, image embedding processing, color conversion processing, and image processing are not described. 2 is different from that shown in FIG. 2 in that the signal is sent to the recording signal conversion process in step S4 through the multi-value error diffusion process in step S8 after the image process in step S3. Here, in the image embedding process in step S7, the binary image data to be embedded is embedded in the ghost image data in a state inclined at a certain angle.
[0033]
Here, the multilevel error diffusion processing in step S8 of FIG. 9 will be described in detail when the error diffusion processing is quaternary, that is, in the case of quaternary error diffusion processing.
In the case of quaternary error diffusion processing, multilevel quantization levels, that is, set density values are 0, 85, 170, and 255, multilevel threshold values are 50, 128, and 210, and error diffusion diffusion coefficients are as shown in FIG. The a position (adjacent in the main scanning direction) may be diffused to 9/16, the b position (down in the sub scanning direction) is 4/16, and the c position may be diffused to 3/16 with respect to the target pixel.
[0034]
Here, the error diffusion processing is four values, and the threshold value and the quantization level as described above are taken. However, other values may be used. The quantization resolution is set to 0 to 255, but other values may be used.
[0035]
In this way, based on the obtained parameter values, multi-value quantization processing is performed by the quantization processing means, and the quantization error generated during the quantization processing is multiplied by a diffusion coefficient by error diffusion processing. Then, it is diffused to a peripheral image area where quantization processing is not performed. In the quantization and error diffusion processing, the target pixel is sequentially scanned in the main scanning direction (raster scanning). When processing for one line is completed, the scan moves to the next line in the sub-scanning direction. Scan sequentially in the direction.
[0036]
For example, consider an image as shown in FIG. FIG. 4A shows four pixel data for one line in the main scanning direction. The four pieces of pixel data are both “43”, which is about half of the quantization level value “85”. First, with respect to the first input pixel, the threshold value and the input pixel data value are compared. In this case, since it is not less than “0” and less than “50”, the quantization level value is converted to “0”. The conversion error is “43-0 = 43”, and this value is multiplied by the diffusion coefficient shown in FIG. As a result, the second pixel data is “ 67 ” obtained by adding the diffusion errors as shown in FIG.
[0037]
Next, like the first pixel, the second pixel is quantized, and the quantization error is diffused to surrounding pixels. As a result, the quantization level value of the second pixel is converted to “85” and the quantization error is “ 67−85 = −18 ” as shown in FIG. Becomes “ 33 ”. Next, the third and fourth pixels are sequentially quantized and error-diffused. The results are as shown in FIGS. As shown in FIG. 5E, one out of two sets of pixels having half the pixel data of the quantization level value “85” is converted into the quantization level value “85”.
[0038]
That is, when the first and second pixels are viewed macroscopically, the density of that portion appears to be about “43”, which is half of “85”. As a result of performing multi-value error diffusion processing, the gradation of the image when viewed as a macro region is maintained, and an image based on the input image data is obtained.
[0039]
Here, as described above, in the error diffusion process, the pixel of interest is raster-scanned in the main scanning direction, and the peripheral pixels where the error is diffused are pixels around the pixel of interest (there is no gap between one pixel). As for each pixel for recording an image used in the alternating drive system of the heating element, the adjacent pixel in the main scanning direction must be “0” data, and the pixel to which the error should be diffused is not adjacent. turn into.
[0040]
In addition, the most adjacent pixel of each pixel for recording an image used for the alternating drive method of the heating element is a pixel diagonally below the target pixel, and the pixel that diffuses the error most is the next in the scan direction of the target pixel. It is no longer a pixel. For this reason, when normal error diffusion processing is performed on pixel data input to a recording engine to which an alternating heating element driving method is applied, the quantization error is not diffused well, and the gradation of the image when viewed as a macro region Will not be maintained.
[0041]
For this reason, in this embodiment, error diffusion is performed by a process such as the flowchart shown in FIG. First, the YMC or YMCK monochromatic pixels input through the image processing in step S3 (original image) are rearranged into a staggered arrangement after performing desired data processing (step S11). Next, a process of rearranging the pixels arranged in the staggered arrangement into a line of lines in the main scanning direction and the sub-scanning direction is performed (step S12), and then the above-described quantization processing and error diffusion processing are performed. (Step S13). Finally, the pixels subjected to the error diffusion process are rearranged into the original staggered arrangement (step S14), and the process is terminated.
In this way, the pixel that should diffuse the error can use the nearest neighbor pixel, and it is not necessary to prepare a special error diffusion coefficient.
[0042]
As described above, when the multi-value error diffusion process is performed on the ghost image 3, the printed dots are printed in an appropriately dispersed state. The dots of the binary image 6 embedded in the ghost image 3 are also dispersed together. Here, in order to disperse the dots, some of the dots of the embedded binary image 6 are lost. However, since the error diffusion processing stores the density when viewed from a macroscopic view, The shape of the embedded binary image 6 is retained. If the dots are appropriately dispersed, the human eye perceives the density of the surrounding image by averaging, and therefore the embedded binary image 6 becomes more difficult to perceive. Therefore, the security of the printed matter 1 can be further improved.
[0043]
FIG. 13 is a flowchart showing a processing procedure when printing the face image 2 and the ghost image 3 according to the third embodiment, which will be described below. Since the face image processing is the same as the processing in FIG. 2 (steps S1 to S4), description thereof is omitted. However, in the image processing in step S3, processing for rearranging pixel data only in the face image into a staggered arrangement is added.
[0044]
Since the processing related to the ghost image is the same as the processing in FIG. 2 (steps S1 to S7, S2 to S3), the reduction processing, density reduction processing, image embedding processing, color conversion processing, and image processing are not described. 2 is different from FIG. 2 in that a signal is sent to the recording signal conversion process in step S4 after the binary error diffusion process in step S9 after the image process in step S3. Here, in the image embedding process in step S7, the binary image data to be embedded is embedded in the ghost image data without being inclined at a certain angle. The ghost image does not rearrange the pixels in a staggered arrangement.
[0045]
In the binary error diffusion processing in step S9, the processing described in FIGS. 10 and 11 is performed. Here, the quantization level is only “255”. Normally, “127” is selected as the threshold value, but the threshold value may be determined by a random number in order to disperse the pixels more appropriately and make it difficult to generate noise such as texture.
[0046]
If such binary error diffusion processing is performed, it is not necessary to arrange the dots in a staggered arrangement, and therefore the ratio of losing the pixel data of the embedded binary image 6 can be reduced. Furthermore, since it is not necessary to arrange the dots in a staggered arrangement, it is not necessary to incline the binary image 6 to be embedded. Further, by performing error diffusion, it is possible to appropriately disperse the dots, the embedded binary image 6 can be hardly perceived by humans, and the security of the printed matter 1 can be further improved.
The quantization process is not limited to the error diffusion process, and may be another quantization process such as a dither process.
[0047]
When determining the authenticity of the printed material 1, the ghost image 3 is read by a scanner or the like, the binary image 6 embedded from the read image data is restored, and the authenticity is determined. At this time, if the hologram pattern 7 is in a portion where the binary image 6 is embedded, the hologram pattern 7 is also read together, and the influence must be removed by applying a special filter or the like.
[0048]
However, in the present embodiment, as shown in FIG. 1, the protective layer is formed so that the hologram pattern 7 is not formed in the portion where the binary image 6 of the ghost image 3 is embedded. For this reason, when the authenticity is determined, the influence of the hologram pattern 7 can be eliminated, and no extra processing is required.
[0049]
In the above-described embodiment, the case where the face image is a color multi-value image has been described. However, the present invention is not limited to this, and for example, the face image may be a monochrome multi-value image. Furthermore, the present invention can be applied to a printed matter on which a monochrome multi-value image such as a signature is also printed.
[0050]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a printing method capable of ensuring high security.
[Brief description of the drawings]
FIG. 1 is a diagram schematically illustrating a configuration of a printed material according to a first embodiment.
FIG. 2 is a flowchart showing a processing procedure when printing a face image and a ghost image according to the first embodiment.
FIG. 3 is a schematic diagram showing an example of dot arrangement when the heating elements of the thermal head are alternately driven.
FIG. 4 is a schematic view showing a temperature distribution in an ink layer of a heating element of a thermal head and a thermal transfer ink ribbon.
FIG. 5 is a diagram schematically illustrating a configuration of a printed material according to a second embodiment.
FIG. 6 is a schematic diagram of dot arrangement of an image printed by a melt type thermal transfer recording method.
FIG. 7 is a diagram for explaining an angle in a dot arrangement direction of a printed image.
FIG. 8 is a diagram for explaining an angle in a dot arrangement direction of a printed image.
FIG. 9 is a flowchart showing a processing procedure when printing a face image and a ghost image according to the second embodiment.
FIG. 10 is a diagram for explaining a diffusion coefficient of error diffusion.
FIG. 11 is a diagram illustrating an example of pixel data when quantization processing and error diffusion processing are performed.
FIG. 12 is a flowchart schematically showing the flow of an image processing method.
FIG. 13 is a flowchart showing a processing procedure when printing a face image and a ghost image according to the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Printed matter, 2 ... Face image, 3 ... Ghost image, 4 ... Character (binary image), 5 ... Pattern, 6 ... Binary image (embedding image), 7 ... Hologram pattern (security pattern), 8 ... Dot , 9 ... heating element.

Claims (2)

In a printing method for printing a face image that is a multivalued image on a print medium, a ghost image that is a face image with a reduced density of the face image, and a binary image such as a character, respectively.
In the case of binary images such as face images, ghost images, and characters, which are multi-valued images, even-numbered pixels and odd-numbered pixels are alternately formed for each recording line. The recording pixels are arranged in a staggered manner, and when recording a binary image, the even-numbered pixels and the odd-numbered pixels are arranged as recording pixels in all the recording lines, and a plurality of heating elements are arranged in a line. Printing using a thermal transfer recording method that performs thermal transfer recording using an arrayed thermal head,
In addition, the ghost image is obtained by subjecting binary image data related to an image printed on the print medium to predetermined processing on the binary image data, and at recording pixel positions arranged in a staggered manner . A printing method characterized in that printing is performed by embedding in a face image having a reduced density of the face image inclined by 45 degrees with respect to the recording line direction . In a printing method for printing a face image that is a multivalued image on a print medium, a ghost image that is a face image with a reduced density of the face image, and a binary image such as a character, respectively.
In the case of binary images such as face images, ghost images, and characters, which are multi-valued images, even-numbered pixels and odd-numbered pixels are alternately formed for each recording line. The recording pixels are arranged in a staggered manner, and when recording a binary image, the even-numbered pixels and the odd-numbered pixels are arranged as recording pixels in all the recording lines, and a plurality of heating elements are arranged in a line. Printing using a thermal transfer recording method that performs thermal transfer recording using an arrayed thermal head,
In addition, the ghost image is obtained by subjecting binary image data related to an image printed on the print medium to predetermined processing on the binary image data, and at recording pixel positions arranged in a staggered manner . The image is embedded in a face image having a reduced face image density by tilting 45 degrees with respect to the recording line direction, and the image data in which the binary image data is embedded is subjected to quantization processing for each pixel. A printing method, comprising: printing image data obtained by performing error diffusion processing on the peripheral pixels of the quantized pixel from a range of peripheral pixels that diffuse the quantization error and a diffusion coefficient for each peripheral pixel.

Images