CN104859329B - A kind of moir patterns method for anti-counterfeit based on linear grating - Google Patents

Abstract

The invention discloses a moiré anti-counterfeiting method based on a linear grating, specifically: step 1, establishing a background color block, and separating four channels in the background color block; step 2, performing screen processing on each channel respectively , where the channels for embedding hidden information have a straight line shape, and the other channels are circular; step 3, make a hidden image; step 4, make a digital image containing hidden information; step 5, make a linear grating; step 6, extract the hidden information. The invention embeds hidden information into a certain channel screened by a straight line, other channels are screened with conventional dots, and finally the hidden information is extracted by means of a matched linear raster. The present invention achieves a very good hiding effect in the digital image after embedding hidden information; when extracting hidden information, the hidden information is highlighted through the strong contrast of the area density and the color display of the hidden channel, and the clarity of the hidden information is improved, thereby Improved moiré anti-counterfeiting quality.

Description

A Moiré anti-counterfeiting method based on linear grating

technical field

The invention belongs to the field of printing anti-counterfeiting and relates to a moiré anti-counterfeiting method based on a linear grating.

Background technique

Moiré anti-counterfeiting is an anti-counterfeiting technology based on the combination of halftone screening technology and Moiré effect. This method is simple and easy to implement, does not require too much equipment and printing technology, and can achieve the purpose of anti-counterfeiting without increasing production costs. Therefore, moiré anti-counterfeiting is a promising anti-counterfeiting method. However, the clarity of the hidden information extracted by the current anti-counterfeiting method is not good, and its anti-counterfeiting quality needs to be improved, so that it can be better applied in actual production.

Contents of the invention

The object of the present invention is to provide a moiré anti-counterfeiting method based on a linear grating, which solves the problems of poor clarity and low anti-counterfeiting quality of the existing moiré anti-counterfeiting method for extracting hidden information.

The technical solution adopted in the present invention is a moiré anti-counterfeiting method based on a linear grating, which is specifically implemented according to the following steps:

Step 1, establish a background color block, and separate the four channels of cyan C, magenta M, yellow Y, and black K in the background color block;

Step 2, screen processing:

Each channel is processed with the custom screening function, among which the channel embedded with hidden information has a dot shape of a straight line, and the dot shape of the other channels is a circle;

Step 3, making a hidden image;

Step 4, making a digital image with hidden information:

Embedding the hidden image made in step 3 into the hidden channel selected in step 2, merging four channels to form a digital image containing hidden information;

Step 5, making a linear grating;

Step 6, extract hidden information:

Superimpose the linear grating produced in step 5 on the digital image containing hidden information produced in step 4, so that the hidden information can be revealed through the strong contrast between the hidden area and the non-hidden area.

The present invention is also characterized in that,

In step 1, the size of the background color block image is 1-10cm×1-10cm, the resolution is 350dpi-2800dpi, the CMYK color mode is adopted, and the dot area ratio of the foreground colors C, M, Y, K is 20%-80%.

In step 2, the screen processing method adopted is halftone screen, the parameters are set to output resolution 350dpi-2800dpi, and the frequency is 80LPI-200LPI.

Step 3 is as follows: first draw the hidden information graphics in Coreldraw software, the size of the canvas is the same as the image size of the background color block, and save it in AI format; then open the graphics in Photoshop, rasterize the image size and The resolution is the same as that of the background color patch.

Step 4 is specifically: copy the layer of the hidden image made in step 3 to the hidden channel image file selected in step 2, activate the image selection area and delete the layer, keep only the outline of the hidden graphic, and use the moving tool to move the selection area Move to form an image embedded with hidden information of the channel, and then combine the four channels to obtain a digital image containing hidden information, and the value of the moving parameter is determined by the hidden algorithm.

The hidden algorithm is specifically:

Among them, X is the moving distance in the horizontal direction, Y is the moving distance in the vertical direction, D is the spacing between the screen lines, D=25.4/L, L is the number of screen lines, and α is the screen angle.

Step 5 is specifically as follows: create a grayscale image with the same size and resolution as the background color block, fill the foreground color, and determine the dot area ratio of the foreground color according to the matching algorithm, and perform halftone screen screening on the image, and the number of screen lines The number of screen lines is the same as that of the background color block, and the screen angle is the same as that of the channel embedded with hidden information, so that a linear raster is obtained.

The matching algorithm is specifically: when the dot area ratio T1 _of the hidden channel is less than 50%, and the dot area ratios of the linear grating and the hidden channel are complementary, then the dot area ratio T2 of the linear grating is ₁ -T1 _; when the dot area ratio of the hidden channel Dot area ratio T ₁ ≥ 50%, linear grating covers the screened straight line of the hidden channel, that is, T ₂ ≥ T ₁ , since the density of the non-hidden area is the lowest, it should form a strong contrast with the hidden area, that is, T ₂ takes the minimum value, then the straight line The dot area ratio T ₂ of the grating is equal to T ₁ , that is, the specific formula of the matching algorithm is:

In step 6, the hidden area is composed of the moving screen line and the raster line, which is a solid ground area; the non-hidden area is composed of the screen points of other channels and the raster line, and is a mesh area with gaps.

The beneficial effect of the present invention is that a moiré anti-counterfeiting method based on a linear grating in the present invention is to embed hidden information into a certain channel through linear screening, other channels are screened with conventional dots, and finally with the help of matching Rectilinear rasters extract hidden information. The anti-counterfeiting method achieves a good hiding effect in the digital image after embedding hidden information; when extracting hidden information, through the strong contrast of area density and the color display of hidden channels, the hidden information is highlighted, and the clarity of hidden information is improved. Thereby improving the moiré anti-counterfeiting quality.

Description of drawings

Fig. 1 is a hidden algorithm geometric analysis diagram of the present invention;

Fig. 2 is a hidden effect diagram in the embodiment of the present invention;

Fig. 3 is a linear grating effect diagram in an embodiment of the present invention, wherein a is a complete effect diagram, and b is a partially enlarged effect diagram;

Fig. 4 is an effect diagram of displaying hidden information in an embodiment of the present invention, wherein a is a complete effect diagram, and b is a partially enlarged effect diagram.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

A moiré anti-counterfeiting method based on a linear grating of the present invention is specifically implemented according to the following steps:

Step 1, create a background color block:

Create an image in Photoshop with a size of 1-10cm×1-10cm and a resolution of 350dpi-2800dpi, using CMYK color mode, and the dot area ratio of the foreground color Cyan C, Magenta M, Yellow Y, and Black K is 20%-80 %; Separate the four channels of cyan C, magenta M, yellow Y, and black K to form image files of the four color channels. .

Step 2, screen processing:

Each channel is processed with the self-defined screening function, and the adopted method is: half-tone screen, the parameters are set to output resolution 350dpi-2800dpi, and the frequency (number of screening lines) is 80LPI-200LPI. Among them, the dot shape of the channel embedded with hidden information is a straight line, and the dot shape of the other channels is circular.

Step 3, Make a hidden image:

First draw the hidden information graphics in the Coreldraw software, the size of the canvas is the same as the image size of the background color block, and save it in AI format. Then open it in Photoshop, and the size and resolution of the image in the rasterization parameter settings are the same as those of the background color block.

Step 4, making a digital image with hidden information:

Copy the hidden layer made in step 3 to the hidden channel image file selected in step 2, activate the image selection area and delete the layer, only keep the outline of the hidden graphic, move the selection area with the move tool, and move the parameters The value is determined by the hidden algorithm, and the formula of the hidden algorithm is as follows:

Among them, X is the moving distance in the horizontal direction, Y is the moving distance in the vertical direction, N is the distance between the screen lines, N=25.4/L, L is the number of screen lines, and α is the screen angle.

A channel image containing hidden information is formed by moving the selection area, and then the four channels are combined to form a digital image containing hidden information.

Step 5, make a linear raster:

Create a new grayscale pattern file in Photoshop with the same size and resolution as the background color block, and the area ratio of the dots of the foreground color to be filled is determined according to the matching algorithm. The matching algorithm is as follows:

For clearly extracting hidden information, it is required that when the dot area ratio T _of the hidden channel is less than 50%, the dot area ratio of the linear grating and the hidden channel is complementary, then the dot area ratio T of the linear grating is ₁ -T1 _; If the dot area ratio T ₁ of the channel is greater than or equal to 50%, the linear grating is required to cover the screened straight line of the hidden channel, that is, T ₂ ≥ T ₁ , and the density of the non-hidden area is required to be the lowest, and it is in strong contrast with the hidden area, that is, T ₂ takes the minimum value, then the dot area ratio T ₂ of the linear grating is T ₁ . That is, the specific formula of the matching algorithm is:

After filling the foreground color according to the matching algorithm, perform straight line screen screening, the number of screen lines is the same as that of the background color block, and the screen angle is consistent with the screen angle of the channel embedded with hidden information, forming a linear raster.

Step 6, extract hidden information:

Copy the linear raster layer made in step 5 to the digital image containing hidden information made in step 4 to reveal the hidden information. For the hidden area, it is composed of the moving screen line and the raster line, which is a solid ground area; while for the non-hidden area, it is formed by the combination of the screen dots of other channels and the raster line, which is a gap. mesh area. Hidden information is highlighted by the strong contrast of region densities and the color revealing of hidden channels.

The present invention is a moiré anti-counterfeiting method based on a linear grating, which embeds hidden information on a certain color plate screened by a straight line, screens other color plates with conventional dots, and finally extracts hidden information by means of a matched linear grating. The present invention achieves a good hiding effect in digital images embedded with hidden information; when extracting hidden information, the present invention highlights the hidden information through the strong contrast of area density and the color display of hidden channels, and improves the clarity of hidden information display , thereby improving the anti-counterfeiting quality of moiré pattern.

Now take the hidden information embedding green version as an example to specifically illustrate the production and operation process of the present invention.

Step 1, create a background color block:

Create an image with a size of 3cm×3cm and a resolution of 2400dpi in Photoshop, the color mode is CMYK, and the dot area ratio of the fill foreground color C, M, Y, and K is 20% respectively. For C, M, Y, and K The channels are separated to form image files for each of the four color channels.

Step 2, screen processing;

Perform "image/mode/bitmap" processing on the four channel images respectively, the parameters are set to output resolution 2400dpi, the method adopted is halftone screen, the frequency (number of screen lines) is 175LPI, and the dot shape of channel C is straight line. The dot shapes of the remaining channels are circular, and the screen angles of C, M, Y, and K channels are 15°, 75°, 90°, and 45° respectively. After setting, perform "image/mode/grayscale" processing, and the conversion ratio is 1.

Step 3, Make a hidden image:

First draw hidden information graphics in the Coreldraw software (the hidden image in this embodiment is the four Chinese characters of "Shaanxi Science and Technology"), the canvas size is 30mm * 30mm, and save it as AI format. Then open it in Photoshop, the size of the image in the rasterization parameter setting is 3cm×3cm, and the resolution is 2400dpi.

Step 4, making a digital image with hidden information:

Copy the hidden image made in step 3 to the C channel image file through "Copy Layer", use the magic wand tool to activate the image selection area and delete the layer, only keep the outline of the hidden graphic, and then execute "Filter/Other/Displacement " process, and calculate the pixel values that move in the horizontal and vertical directions respectively according to the hidden algorithm, specifically: as shown in Figure 1, to move the straight line where A is to the straight line where O (the midpoint of AB) is, you need to perform horizontal Separate movement with the vertical direction, ie AD and OD. According to the geometric relationship of the triangle, the specific formula of the hidden algorithm is:

Among them, AB=25.4/L, L is the number of screen lines, and α is the screen angle.

The calculation result is: move 2 pixels to the right horizontally, move -7 pixels vertically down, move the selected area to form the hidden image of the C channel, and then merge the four channels to finally form a digital image with hidden information. The effect is shown in Figure 2 Show.

Step 5, make a linear raster:

Create a new one in Photoshop with a size of 3cm×3cm, a resolution of 2400dpi, and a color mode of grayscale. According to the matching algorithm, because T ₁ is 20%, then T ₂ is 80%, that is, the filled foreground colors C, M, and Y are all 0, and K is 80%, and "image/mode/bitmap" processing is performed, and the parameters The output resolution is set to 2400dpi, the method used is halftone screen, the frequency (number of screen lines) is 175LPI, the shape is a straight line, and the angle is 15° to form a matching linear raster. The effect is shown in Figure 3, 3a is a complete rendering, and 3b is a partially enlarged rendering.

Step 6, extract hidden information:

Copy the linear raster layer produced in step 5 to the digital image file containing hidden information produced in step 4 to reveal the hidden information. The effect is shown in Figure 4, where 4a is the complete rendering and 4b is the partial enlarged rendering. It can be seen from Figure 4b that for the hidden area, it is composed of the moving screen straight line and the raster line, which is a solid ground area, while for the non-hidden area, it is a combination of the screen points of other channels and the raster line Formed, is a mesh region with gaps. The hidden information is highlighted through the strong contrast of the area density and the color of the hidden channel, so that it can achieve the complete effect as shown in Figure 4a.

Claims (7)

1. A moiré anti-counterfeiting method based on linear grating, is characterized in that, specifically implements according to the following steps: Step 1, establish a background color block, and separate the four channels of cyan C, magenta M, yellow Y, and black K in the background color block; Step 2, screen processing: Use the custom screening function to process each channel separately. For the channel embedded with hidden information, the dot shape of the channel is a straight line, and the dot shape of the other channels is circular; Step 3, making a hidden image; Step 4, making a digital image with hidden information: Embedding the hidden image made in step 3 into the hidden channel selected in step 2, merging four channels to form a digital image containing hidden information; Step 5, make a linear raster: Create a new grayscale image with the same size and resolution as the background color block, fill the foreground color, and determine the dot area ratio of the foreground color according to the matching algorithm, and perform halftone screen screening on the image, and add the number of screen lines and the background color block. The number of screen lines is the same, the screen angle is consistent with the screen angle of the channel embedded with hidden information, and a linear grating is obtained; The matching algorithm is specifically: when the dot area ratio T1 of the hidden channel is less than 50%, and the dot area ratios of the linear grating and the hidden channel are complementary, then the dot area ratio T2 of the linear grating is 1-T1; when the dot area ratio of the hidden channel The area ratio T1≥50%, the linear grating covers the screened straight line of the hidden channel, that is, T2≥T1, since the density of the non-hidden area is the lowest and should form a strong contrast with the hidden area, that is, T2 takes the minimum value, then the dot area ratio of the linear grating T2 is equal to T1, that is, the specific formula of the matching algorithm is: $\left\{\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}& <span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 50</span>}\mathrm{<span\; class="notranslate">\; \%</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}& <span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span>\mathrm{<span\; class="notranslate">\; 50</span>}\mathrm{<span\; class="notranslate">\; \%</span>}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; ;</span>$ Step 6, extract hidden information: Superimpose the linear grating produced in step 5 on the digital image containing hidden information produced in step 4, so that the hidden information can be revealed through the strong contrast between the hidden area and the non-hidden area. 2. A moiré anti-counterfeiting method based on a linear grating according to claim 1, wherein the size of the background color block image in the step 1 is 1-10cm×1-10cm, and the resolution is 350dpi-2800dpi , using CMYK color mode, and the foreground color C, M, Y, K dot area ratio of 20% to 80%. 3. A kind of moiré anti-counterfeiting method based on linear grating according to claim 1, characterized in that, in the step 2, the method adopted for screen processing is halftone screen, and the parameters are set to an output resolution of 350dpi～ 2800dpi, the frequency is 80LPI～200LPI. 4. A kind of moiré anti-counterfeiting method based on linear grating according to claim 1, characterized in that, said step 3 is specifically: first draw the image of hidden information graphics, canvas size and background color block in Coreldraw software The size is the same, and it is saved in AI format; then the graphic is opened in Photoshop, and the image size and resolution in the rasterization parameter settings are the same as those of the background color block. 5. A moiré anti-counterfeiting method based on a linear grating according to claim 1, wherein said step 4 is specifically: copying the hidden image made in step 3 to the selected one in step 2. In the hidden channel image file, activate the image selection area and delete the layer, only keep the outline of the hidden graphic, move the selection area with the moving tool to form an image embedded with hidden information of the channel, and then merge the four channels to obtain the image containing For digital images with hidden information, the value of the movement parameter is determined by the concealment algorithm. 6. A kind of moiré anti-counterfeiting method based on linear grating according to claim 5, characterized in that, the concealment algorithm is specifically: Among them, X is the moving distance in the horizontal direction, Y is the moving distance in the vertical direction, D is the spacing between the screen lines, D=25.4/L, L is the number of screen lines, and α is the screen angle. 7. A moiré anti-counterfeiting method based on a linear grating according to claim 1, wherein the hidden area in the step 6 is formed by combining the moved screened straight line and the straight line of the grating, and is a solid surface Area; the non-hidden area is composed of the dots of other channels and the straight lines of the raster, and is a mesh area with gaps.