CN108898541A - Linear grating matching method based on dot percentage and number of added grids - Google Patents
Linear grating matching method based on dot percentage and number of added grids Download PDFInfo
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Abstract
The invention discloses a linear grating matching method based on dot percentage and added screen number, which comprises the following steps: step one, preparing an original and preprocessing; step two, hiding the anti-counterfeiting information; and step three, extracting the anti-counterfeiting information. The invention carries out micro-processing on the dots of the screened image of the original manuscript and designs the corresponding linear grating, breaks through the technical bias, improves the encoding concealment and the extraction identification, and simultaneously reduces the operation difficulty.
Description
Technical Field
The invention belongs to the technical field of grating anti-counterfeiting, and particularly relates to a linear grating matching method based on dot percentage and added screen lines.
Background
The limit resolution capability of the normal vision of human eyes is limited, and when the size and the dot spacing of the image dots after digital screening are smaller than the limit resolution capability of the vision of human eyes, the human eyes cannot distinguish the dots. Therefore, actually, a discretized binary image is discontinuous, but dots cannot be distinguished at all, that is, details of the image cannot be distinguished if the binary image is viewed at a certain viewing distance due to the visual characteristics of human eyes, and finally, an image effect of continuous tone is given to people, so that printing and copying of the continuous tone original are realized.
The grating anti-counterfeiting technology is generated by combining a halftone screening technology and a moire effect, a row of lattice points of a halftone image are regarded as a black straight line, and then the black straight line is superposed with a digital grating with the same period and width to form a longitudinal moire fringe with an infinite period, wherein the digital grating is designed by simulating the optical characteristics of a black-and-white grating on a computer. Black and white gratings are made up of a large number of very fine parallel stripes alternating between black and white. Ideally, the black stripes should be completely opaque, i.e., have zero transmittance, and the white stripes, i.e., the slits, have 100% transmittance.
The information hiding stage of grating anti-counterfeiting, the prior art is the dot displacement method, is finished by changing the position of some dots, all the dot after moving is whole to form the new hidden information pattern, it is a hidden algorithm to hide the anti-counterfeiting information needing to be imbedded, because this kind of low-pass filtering characteristic of the human vision, after carrying on the amplitude modulation screening treatment to the halftone host figure, the whole changes some dot positions of the local area, because the dot is very small, the trace its position will not be obvious to cause the human eye to perceive, imbed the hidden information into the host image on the basis of this kind of principle, and will not cause the perception of the human eye vision; then, the corresponding grating is utilized to display the whole hidden information formed by all the moved net points when the hidden information is detected.
The algorithm formula of the dot displacement method is as follows:wherein X and Y respectively represent the displacement of the dots in the transverse direction and the longitudinal direction, D represents the distance between two adjacent dots in the screening direction, namely the actual moving distance of the dots is D/2, the unit is mm, because the screening number is inevitably set in the image halftone process, D is a known value,
in the information hiding stage of grating anti-counterfeiting, the prior art is a linear grating extraction method matched with a mesh point displacement method.
Although the dot shift method and the linear grating extraction method are very commonly used, the following defects exist:
(1) in the anti-counterfeiting information hiding stage, when the percentage of the mesh points exceeds 20%, the mesh point overlapping problem is caused by adopting a mesh point displacement method, so that visual perception is caused, and the hiding performance is low;
(2) in the anti-counterfeiting information extraction stage, the extraction performance of the used digital grating is not optimal, and particularly the control problem of the width of the black stripe needs to be further improved;
(3) large workload and complicated operation.
Disclosure of Invention
The invention aims to provide a linear grating matching method based on the dot percentage and the number of screened lines, which is used for microcosmically processing the dots of a screened image of a manuscript and designing a corresponding linear grating, so that the technical bias is broken, the coding concealment and the extraction recognition are improved, and the operation difficulty is reduced.
The invention provides the following technical scheme: a straight line grating matching method based on dot percentage and added screen lines comprises the following steps:
step one, preparing an original and preprocessing
Preparing an original manuscript which is a digital file with a rectangular structure and synthesized by color channels, wherein the color channels consist of 4 channels including a C channel, an M channel, a Y channel and a K channel, reading the dot percentage value of each channel in image processing software, at least one channel in the color channels has an area with the same dot percentage, and the dot percentage value in the area is α and α is 0.1-0.5;
selecting any channel with the same area of the screen dot percentage as an encryption channel, setting screening parameters for 4 channels for screening respectively to obtain an encryption channel halftone picture consisting of screen dots and 3 common channel halftone pictures, wherein the rest channels are 3 common channels;
the screening processing adopts a half-tone screen, the screening parameters comprise output resolution, screening line number and mesh point shape, when the screening processing is respectively carried out on the 4 channels, the same output resolution, screening line number and mesh point shape are adopted, and the output resolution is integral multiple of the screening line number; the shapes of the net points are all round; recording the number of the screening lines as l, and the screening parameters also comprise a screening angle, and recording the screening angle of the encryption channel as theta; the screening angles comprise 0 degree, 18.44 degrees, 45 degrees and 71.57 degrees, theta is 0 degree, and the screening angles of the 3 common channels are any combination of 18.44 degrees, 45 degrees and 71.57 degrees;
step two, hiding the anti-counterfeiting information
(1) And dot displacement: recording areas corresponding to the areas with the same screen dot percentage in the encryption channel halftone graph as encryption areas; selecting anti-counterfeiting information to be hidden, establishing a mesh point selection area in the encryption area according to the profile of the anti-counterfeiting information, recording mesh points in the mesh point selection area as a set A, displacing mesh points of the set A in a vertically upward or vertically downward direction by a displacement distance S, and performing a displacement algorithm:
(2) and image synthesis: after the dot displacement is finished, obtaining a coded encryption channel halftone image, and synthesizing the coded encryption channel halftone image and 3 common channel halftone images to obtain an original halftone image carrying anti-counterfeiting information, so as to finish the hiding of the anti-counterfeiting information; the image synthesis method comprises the following steps:
newly building an image I in the photoshop, wherein the length and the width of the image I are the same as those of the original, the resolution of the image I is the same as the output resolution, the background content is white, the color mode is a CMKY mode, and copying the encoding encryption channel halftone map and the 3 common channel halftone maps into corresponding color channels to obtain the encoding encryption channel halftone map;
step three, extracting anti-counterfeiting information
Preparing a digital file type decoding linear grating, wherein the area of the decoding linear grating is larger than that of the encryption region, the decoding linear grating is composed of black stripes and transparent stripes which are same in length and arranged in parallel at intervals, and the width of each black stripe is T1The width of the transparent stripe is T2，The T is1The calculation method comprises the following steps:
in the image processing software, T is obtained according to calculation1And T2And (3) making to obtain a decoding linear grating, covering the decoding linear grating on the original halftone image, rotating and moving the decoding linear grating for extraction until the anti-counterfeiting information is observed, and finishing the extraction of the anti-counterfeiting information.
As a further description of the above technical solution:
in the second step, the displacement algorithm is as follows:
as a further description of the above technical solution:
in the third step, T1The calculation method comprises the following steps:
as a further description of the above technical solution:
in the first step, the original document is a digital file opened by adopting photoshop software, the screening processing adopts a half-tone screen in photoshop, and the method for screening each channel comprises the following steps: and selecting a channel, converting the channel into a bitmap, setting the output resolution during conversion, and then screening the channel by adopting a half-tone screen.
As a further description of the above technical solution:
the number of the screened lines is 96lpi, and the output resolution is 2400 dpi.
As a further description of the above technical solution:
in the second step, the dot displacement further comprises dot percentage improvement, and then image synthesis is performed, wherein the dot percentage improvement method comprises the following steps:
recording a set of the net points on the boundary of the net point selection area in the set A as B, wherein B belongs to A, recording a set of the net points which are outside the net point selection area and are closest to the net point selection area in the encryption channel as G, and adapting the outline formed by the net points in the set G to the outline formed by the net points in the set B; when the mesh point displacement is carried out, the motion states of the mesh points of the set B relative to the mesh points of the set G comprise far motion, close motion and parallel motion; the set of net points of the approach motion is B1The set of dots of the far motion is B2After the dot displacement is finished, the set B is processed1The screen dot percentage of the screen dot is improved, and the improved screen dot percentage is α1'：
Then to set B2The screen dot percentage of the screen dot is improved, and the improved screen dot percentage is α2'：
Set B2After the dot percentage improvement is completed, copy set B2To obtain a set B2', and will set B2' mesh points in move to set B2And the halftone image of the coding encryption channel is obtained between the halftone dots corresponding to the set G.
As a further description of the above technical solution:
the anti-counterfeiting information is characters and/or graphs.
As a further description of the above technical solution:
the anti-counterfeiting information is characters, the website displacement is completed by adopting photoshop software, and the method for establishing the website selection area comprises the following steps:
(1) newly building an image II in the photoshop, wherein the length and the width of the image II are the same as those of the original, the resolution of the image II is the same as the output resolution, the background content is white, obtaining 'layer 0' in a layer channel, copying the encryption channel halftone map into the image II to obtain 'layer 1', copying 'layer 1' to obtain 'layer 2'; arranging the layer 2, the layer 1 and the layer 0 in the layer window in sequence;
(2) selecting a character tool, inputting anti-counterfeiting information to obtain a layer 3, selecting the anti-counterfeiting information by using a magic stick tool to obtain a dot selection area, and setting the layer 3 to be invisible.
As a further description of the above technical solution:
the anti-counterfeiting information is a graph, the website displacement is completed by adopting photoshop software, and the method for establishing the website selection area comprises the following steps:
(1) newly building an image III in the photoshop, wherein the length and the width of the image III are the same as those of the original, the resolution of the image III is the same as the output resolution, the background content is white, obtaining 'layer 0' in a layer channel, copying the encryption channel halftone map into the image III to obtain 'layer 1', copying 'layer 1' to obtain 'layer 2'; arranging the layer 2, the layer 1 and the layer 0 in the layer window in sequence;
(2) and putting anti-counterfeiting information to obtain a 'layer 3', selecting the anti-counterfeiting information by using a magic stick tool to obtain a dot selection area, and setting the 'layer 3' to be invisible.
The invention has the beneficial effects that: the method comprises the following steps of microcosmically processing the dots of the screened image of the original manuscript, designing a corresponding linear grating, breaking through the technical bias, improving the encoding concealment and the extraction identification, and simultaneously reducing the operation difficulty, and specifically comprises the following steps:
1. in the anti-counterfeiting information hiding stage, based on the low-pass filtering characteristic of human vision, after the original is subjected to amplitude modulation screening processing, the positions and the percentages of the dots in the local area in the anti-counterfeiting channel are changed, and the anti-counterfeiting information is embedded into the original image, so that the aim of hiding the anti-counterfeiting information is fulfilled; compared with the prior art, the advantages are that:
(1) in actual operation, multiple experimental tests show that when the dot percentage is less than 0.1, the concealment of the anti-counterfeiting information is very good, but the extraction and identification performance is extremely poor; when the dot percentage is more than 0.5, the extraction and identification performance of the anti-counterfeiting information is good, but the concealment is weak, and in order to achieve the best concealment and extraction, only the dot percentage between 0.1 and 0.5 is adopted in the invention; in addition, in actual operation, when the dot percentage reaches 0.5, in a halftone image after being screened by photoshop (the dot shape is circular), two adjacent dots are already in contact with each other under the condition that no displacement is generated, so that the set B1The mesh points can be lapped when moving at any time;
(2) dot shift method for realizing moire effect, consider all dots to be shifted the same, but set B1The distance that the mesh point can actually move is the distance between the closest points of the two mesh pointsD1In the prior art in the field, no deep research has been conducted on the movable distance of the boundary dots, and few of them are limited to the subjective judgment and theoretical basis of shallow layers, according to the dot displacement method, the distance of all dots to be moved is D/2, and the moving direction is the direction of the screening angle (i.e. along the formed screen line direction)1At the moment, the moved mesh points just contact with the mesh points in front of the moved mesh points but are not overlapped, because the screening parameters are set in the previous half-tone processing, the screening number is a known number, and the screening number determines the distance D between two adjacent mesh points and the side length D of a mesh tone unit2，D＝D2Distance D between nearest points of two dots1Equal to the distance D between two adjacent dots minus the value of two radii r, D being equal to the sum of the two radii r1Then, depending on the dot radius r, which depends on the dot percentage α, the following equation is obtained:
thus, when D/2 equals D1When the temperature of the water is higher than the set temperature,at the moment, the moved mesh point is just contacted with the mesh point in front of the moved mesh point but is not overlapped, the mesh point is influenced by the output resolution in the photoshop, and the shape of the mesh point is not necessarily in a standard circle, so that α is taken as an integer of 0.2, and α is 0.2 as a threshold value;
while moving the dots according to the traditional dot shift method, set B1The mesh points in the anti-counterfeiting information extraction device can be lapped with mesh points in front of the moving direction of the anti-counterfeiting information extraction device, the lapping of the mesh points can cause a very large negative effect on the concealment of the anti-counterfeiting information, the visual perception of the lapping part is very obvious, particularly, the mesh points of the lapping part or the mesh points on the boundary can enable the outline of the anti-counterfeiting information to be perceived by human eyes before extraction, so that the anti-counterfeiting function is invalid, therefore, in the anti-counterfeiting information extraction device, when α is less than or equal toSome net point displacement methods adopt X and Y to respectively represent the transverse displacement and the longitudinal displacement, carry out net point displacement on the net points of the set A,within the range, the hiding and the extraction of the anti-counterfeiting information can be realized, wherein,in time, the extraction and identification performance is optimal, and the displacement algorithm can be expressed as follows:
0.1≤α≤0.2；
(3) when α is more than 0.2, the mesh point is moved according to the traditional mesh point displacement method (i.e. D/2 is moved in the screening direction), and the set B1The mesh points in the anti-counterfeiting information extraction system can be lapped with mesh points in front of the moving direction of the anti-counterfeiting information extraction system, the lapping of the mesh points can cause a very large negative effect on the concealment of the anti-counterfeiting information, the visual perception of the lapping part is very obvious, and particularly, the mesh points of the lapping part are also mesh points on the boundary, so that the outline of the anti-counterfeiting information is perceived by human eyes before extraction, and the anti-counterfeiting function is invalid;
to ensure a certain concealment while ensuring the set B1Can make contribution to extracting identification when the moving distance is greater than 0 and less than or equal to D1During the process, the hiding and the extraction of the anti-counterfeiting information can be realized, and the method specifically comprises the following steps:
0＜S≤D1；
and because:
therefore, the algorithm for shifting the dots in the set a in the horizontal and vertical directions is as follows:
multiple experimental tests show that when the net point moves to the maximum distance D1The extraction performance is optimal.
The information hiding method can improve the hiding performance and the extraction identification performance at the same time, reduce the workload, and has stronger pertinence, meanwhile, in the operation, the dot displacement is firstly carried out and then the dot percentage is improved, the purpose of further improving the dot percentage is to improve the hiding performance, after the dot displacement, a dot far away from the moving dot generates a larger gap with the surrounding dots, but is close to the moving dot, and the dot forms a dense dot area with the dot in front of the moving direction, if the dot percentage is not improved, a part of the dots are too sparse, and the other part of the dots are too dense, so that the visual perception is caused, in addition, the improvement method can reduce the workload and reduce the operation difficulty, effectively avoid the generation of errors, and simultaneously, the dot on the boundary contributes to the improvement of the hiding performance and the identification performance; the improvement coefficient of the dot percentage is made after a large number of experimental tests are carried out on the invention;
2. in the anti-counterfeiting information extraction stage, the invention researches the defects of the decoding linear grating in the prior art to carry out comprehensive and scientific improvement, and in the prior art, T in the decoding linear grating designed for forming moire fringes12r, the anti-counterfeiting information extracted and identified in the invention is not only based on moire fringes, but also based on contrast, and multiple experimental tests show that when the percentage of the mesh points in the set A is 0.1- α -0.2, T is less than or equal to1Has a width of 2r ≤ T1< S, i.eThe decoding linear grating prepared in the range can clearly extract anti-counterfeiting information, not only T1The anti-counterfeit information can be extracted only when the value is 2r, and in the embodiment, the T is followed1Is increased, extractedThe contrast is increased at the same time, so that the anti-counterfeiting information can be more easily identified in the extraction process; and because ofThus, it is possible to provideIs equivalent to:
multiple experimental tests show that when the screen dots are more than 0.2 and less than α and less than or equal to 0.5, the screen dots in the range are denser, if the screen dots are continuously increased, the extraction and identification performance is not greatly improved,in time, the extraction performance of the grating recognition reaches the best; thus T1The calculation method comprises the following steps:
the invention has the advantages that the grating is designed in a targeted manner, the technical bias that anti-counterfeiting information can be obtained only based on Moire patterns in the prior art is broken through, the covering width of the decoding linear grating is designed, and the definition and the identification degree of the grating during decoding are improved as much as possible, so that the anti-counterfeiting information can be verified more conveniently during use;
3. the preparation method of the dot selection area is simpler and more accurate, and is directly manufactured on the halftone image of the anti-counterfeiting channel and adjusted, so that the dots in the selection area are all complete dots;
4. according to the invention, the extraction effect can be prefabricated, the anti-counterfeiting information is coded in the image, and the corresponding analog extraction linear grating is manufactured, so that the anti-counterfeiting information can be detected by using the analog extraction linear grating for extraction before the image is printed and output, the detection effect is prefabricated, the hidden image can be conveniently checked, the early warning effect is realized, and the corresponding data can be conveniently adopted for manufacturing the real object grating sheet in the subsequent process;
5. the original manuscript can be directly made in image processing software, or can be randomly selected to meet the conditions in the step 1, the application range is wider and more flexible, then the dot percentage value is read in the image processing software, and different displacement algorithms and dot percentage algorithms are changed according to different dot percentages;
6. the screening angle of the encryption channel is 0 degrees, the encoding difficulty of the hidden anti-counterfeiting information can be reduced, the direction of the displacement of the mesh points is upward or downward, and the operation is more convenient.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
FIG. 1 is an original (color information not shown) in embodiment 1 of the present invention;
FIG. 2 is a halftone map of an encryption channel in embodiment 1 of the present invention;
FIG. 3 is a partially enlarged schematic view of a halftone map of an encryption channel in embodiment 1 of the invention of FIG. 2;
FIG. 4 is a halftone map of an original carrying forgery prevention information (color information not shown) in embodiment 1 of the present invention;
FIG. 5 is a graph (color information not shown) of anti-counterfeit information extraction by analog decoding in example 1 of the present invention;
FIG. 6 is a graph (color information not shown) of anti-counterfeit information extraction by analog decoding in example 2 of the present invention;
FIG. 7 is a diagram illustrating analysis of motion states of dots in an embodiment of the present invention;
FIG. 8 is an original (color information not shown) in embodiment 3 of the present invention;
fig. 9 is an encrypted channel halftone map in embodiment 3 of the present invention;
fig. 10 is a partially enlarged schematic view of a halftone map of an encryption channel in embodiment 3 of the invention of fig. 9;
FIG. 11 is a halftone map of an original carrying forgery prevention information (color information not shown) in embodiment 3 of the present invention;
FIG. 12 is a graph (color information not shown) of anti-counterfeit information extraction by analog decoding in example 3 of the present invention;
fig. 13 is a halftone map of an encryption channel after being covered with a grating in embodiment 3 of the present invention;
labeled as: 1. a first net point; 2. a second screen point; 3. a third screen dot; 4. fourth, a net point; 5. and (5) a mesh point five.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. These examples are intended to illustrate the invention and are not intended to limit the scope of the invention. The structural features of the present invention will now be described in detail with reference to the accompanying drawings.
Example 1
A straight line grating matching method based on dot percentage and added screen lines comprises the following steps:
step one, preparing an original and preprocessing
Preparing an original manuscript which is a digital file with a rectangular structure and synthesized by color channels, wherein the color channels consist of 4 channels including a C channel, an M channel, a Y channel and a K channel, reading the dot percentage value of each channel in image processing software, at least one channel in the color channels has an area with the same dot percentage, and recording that the dot percentage value in the area is α and α is 0.1-0.5;
selecting a channel C as an encryption channel, setting screening parameters for 4 channels to carry out screening processing respectively by using the rest channels as 3 common channels, and obtaining an encryption channel halftone map consisting of screen dots and 3 common channel halftone maps;
the screening processing adopts a half-tone screen, the screening parameters comprise output resolution, screening line number and mesh point shape, when the screening processing is respectively carried out on the 4 channels, the same output resolution, screening line number and mesh point shape are adopted, and the output resolution is integral multiple of the screening line number; the shapes of the net points are all round; recording the number of the screening lines as l, and the screening parameters also comprise a screening angle, and recording the screening angle of the encryption channel as theta; the screening angles comprise 0 degree, 18.44 degrees, 45 degrees and 71.57 degrees, theta is 0 degree, and the screening angles of the 3 common channels are any combination of 18.44 degrees, 45 degrees and 71.57 degrees; the number of the screened lines is 96lpi, and the output resolution is 2400 dpi;
step two, hiding the anti-counterfeiting information
(1) And dot displacement: recording areas corresponding to the areas with the same screen dot percentage in the encryption channel halftone graph as encryption areas; selecting anti-counterfeiting information to be hidden, establishing a mesh point selection area in the encryption area according to the profile of the anti-counterfeiting information, recording mesh points in the mesh point selection area as a set A, displacing mesh points of the set A in a vertically upward or vertically downward direction by a displacement distance S, and performing a displacement algorithm:
in the present embodiment, α is 0.15, and the displacement distance S is preferably set to be equal to
(2) And image synthesis: after the dot displacement is finished, obtaining a coded encryption channel halftone image, and synthesizing the coded encryption channel halftone image and 3 common channel halftone images to obtain an original halftone image carrying anti-counterfeiting information, so as to finish the hiding of the anti-counterfeiting information; the image synthesis method comprises the following steps:
newly building an image I in the photoshop, wherein the length and the width of the image I are the same as those of the original, the resolution of the image I is the same as the output resolution, the background content is white, the color mode is a CMKY mode, and copying the encoding encryption channel halftone map and the 3 common channel halftone maps into corresponding color channels to obtain the encoding encryption channel halftone map;
step three, extracting anti-counterfeiting information
Preparing a digital file type decoding linear grating, wherein the area of the decoding linear grating is larger than that of the encryption region, the decoding linear grating is composed of black stripes and transparent stripes which are same in length and arranged in parallel at intervals, and the width of each black stripe is T1The width of the transparent stripe is T2，The T is1The calculation method comprises the following steps:
in this embodiment, α is 0.15, preferably
In photoshop software, T is obtained according to calculation1And T2And (3) making to obtain a decoding linear grating, covering the decoding linear grating on the original halftone image, rotating and moving the decoding linear grating for extraction until the anti-counterfeiting information is observed, and finishing the extraction of the anti-counterfeiting information.
Wherein,
the manufacturing method of the decoding linear grating comprises the following steps:
(1) opening photoshop software, newly building a layer X, setting the background color to be transparent (no background color), then drawing a first rectangle with a specific length and width value on the built layer by using a rectangle tool, then filling the color (preferably black) in a drawn rectangle frame, drawing a second rectangle with the same width as the first rectangle and the length larger than the first rectangle by using the same method, sleeving the second rectangle on the first rectangle, positioning the first rectangle at the bottom of the second rectangle, then selecting 'editing/defining the pattern', and storing the well-made pattern as 'pattern 0';
(2) and then deleting the layer X, rebuilding a new layer and naming the new layer as a layer Z, wherein the size of the layer Z is the size of the decoding linear grating, the resolution is the same as the output resolution, then filling the layer Z with the stored 'pattern 0', and forming the decoding linear grating for detecting the anti-counterfeiting information after filling.
Wherein,
the length of the first rectangle is T1The length of the second rectangle is T1+T2The length of the first rectangle and the length of the second rectangle can be measured with a ruler, or other conventional methods, to make the width of the resulting black stripe conform to T1The numerical value obtained by the calculation method of (1);
in this embodiment, it is preferable that the number of the screened lines is 96lpi, the output resolution is 2400dpi, the output resolution is an integer multiple of the number of the screened lines, the image layer is enlarged to the maximum in the photoshop, it can be clearly seen that the side length of each halftone unit is 25 small grids, and the length T of the second rectangle is1+T2Namely the side length of the halftone cell,i.e. the distance between two adjacent dots, therefore, in the manufacture of the decoding linear grating, only the T is needed1The operation is simplified, the operation error is reduced and a large amount of workload is reduced by combining the calculated numerical value with the small grid.
Wherein,
in the first step, the original document is a digital file opened by adopting photoshop software, the screening processing adopts a half-tone screen in photoshop, and the method for screening each channel comprises the following steps: and selecting a channel, converting the channel into a bitmap, setting the output resolution during conversion, and then screening the channel by adopting a half-tone screen.
Wherein,
in the second step, the dot displacement further comprises dot percentage improvement, and then image synthesis is performed, wherein the dot percentage improvement method comprises the following steps:
recording a set of the net points on the boundary of the net point selection area in the set A as B, wherein B belongs to A, recording a set of the net points which are outside the net point selection area and are closest to the net point selection area in the encryption channel as G, and adapting the outline formed by the net points in the set G to the outline formed by the net points in the set B; referring to fig. 7, fig. 7 is an analysis diagram of the motion states of the dots, wherein, for the sake of convenience of distinction, assuming that the dots to be displaced are gray and white dots, the black dots enclosed outside the gray dots may be used as the set G in the present embodiment, and when the displacement adjustment is performed, the motion states of the dots of the set B relative to the dots of the set G include a far motion, a near motion, and a parallel motion; the set of net points of the approach motion is B1The set of dots of the far motion is B2(ii) a As can be seen from fig. 7, when θ is 0 °, the displacement direction is vertical upward, at this time, the motion state of the dot one 1 is close motion, the motion state of the dot two 2 is parallel motion, the motion states of the dot three 3 and the dot five 5 are far motion, and the dot four 4 is not displaced; after the net point displacement is completed, the set B is processed1The dot percentage of the screen is improved, and the improved dot percentage isα1'：
Then to set B2The screen dot percentage of the screen dot is improved, and the improved screen dot percentage is α2'：
Set B2After the dot percentage improvement is completed, copy set B2To obtain a set B2And will aggregate B2Moving to set B2And the halftone image of the coding encryption channel is obtained between the halftone dots corresponding to the set G.
Wherein,
the anti-counterfeiting information is characters, the website displacement is completed by adopting photoshop software, and the method for establishing the website selection area comprises the following steps:
(1) newly building an image II in the photoshop, wherein the length and the width of the image II are the same as those of the original, the resolution of the image II is the same as the output resolution, the background content is white, obtaining 'layer 0' in a layer channel, copying the encryption channel halftone map into the image II to obtain 'layer 1', copying 'layer 1' to obtain 'layer 2'; arranging the layer 2, the layer 1 and the layer 0 in the layer window in sequence;
(2) selecting a character tool, inputting anti-counterfeiting information to obtain a layer 3, selecting the anti-counterfeiting information by using a magic stick tool to obtain a dot selection area, and setting the layer 3 to be invisible.
Combining the encrypted channel halftone map and 3 normal channel halftone maps in example 1 to obtain an original halftone map without embedded anti-counterfeiting information, and respectively evaluating the similarity between the original halftone map without embedded anti-counterfeiting information and the original halftone map with anti-counterfeiting information by using an SSIM (structural similarity) algorithm and a WSNR (weighted signal-to-noise ratio), thereby indirectly obtaining an evaluation result of the concealment of hidden information, as shown in table 2 below:
table 1 example 1 evaluation results of similarity
Wherein, the closer the value of SSIM is to 1 or the larger the value of WSNR is, the larger the similarity between two images is, as can be seen from the above Table 1, the value of SSIM of embodiment 1 is close to 1 and WSNR is larger, therefore, the method of the present invention has good hiding effect and is not easy to be perceived by human eyes
Example 2
Referring to fig. 6, on the basis of embodiment 1, the area of embodiment 2 lies in: preference is given toReferring to FIG. 5, the subjective evaluation can be used to obtain the time when the user is looking for the dataThe contrast and the significance of the extracted anti-counterfeiting information are better than those of the extracted anti-counterfeiting informationIn addition, the invention also uses the extraction graphs after the grating coverage of contrast evaluation and significance evaluation, and the same result as the subjective evaluation is obtained.
Example 3
Referring to fig. 7-13, on the basis of embodiment 1, embodiment 3 differs from embodiment 1 in that (1) different originals are used, the read α value is 0.3, (2) the anti-counterfeiting information is a graph, the dot shift is completed by photoshop software, and the method for establishing the dot selection area comprises the following steps:
(1) newly building an image II in the photoshop, wherein the length and the width of the image II are the same as those of the original, the resolution of the image II is the same as the output resolution, the background content is white, obtaining 'layer 0' in a layer channel, copying the encryption channel halftone map into the image II to obtain 'layer 1', copying 'layer 1' to obtain 'layer 2'; arranging the layer 2, the layer 1 and the layer 0 in the layer window in sequence;
(2) and putting anti-counterfeiting information to obtain a 'layer 3', selecting the anti-counterfeiting information by using a magic stick tool to obtain a dot selection area, and setting the 'layer 3' to be invisible.
Combining the encrypted channel halftone map and 3 normal channel halftone maps in example 3 to obtain an original halftone map without embedded anti-counterfeiting information, and respectively evaluating the similarity between the original halftone map without embedded anti-counterfeiting information and the original halftone map with anti-counterfeiting information by using an SSIM (structural similarity) algorithm and a WSNR (weighted signal-to-noise ratio), thereby indirectly obtaining an evaluation result of the concealment of hidden information, as shown in table 2 below:
table 2 example 3 evaluation results of similarity
As shown in table 2, the SSIM value of embodiment 3 is close to 1 and the WSNR is large, so that the method of the present invention has a good concealing effect and is not easily perceived by human eyes.
Claims (9)
1. A linear grating matching method based on dot percentage and added screen number is characterized by comprising the following steps:
step one, preparing an original and preprocessing
Preparing an original manuscript which is a digital file with a rectangular structure and synthesized by color channels, wherein the color channels consist of 4 channels including a C channel, an M channel, a Y channel and a K channel, reading the dot percentage value of each channel in image processing software, at least one channel in the color channels has an area with the same dot percentage, and the dot percentage value in the area is α and α is 0.1-0.5;
selecting any channel with the same area of the screen dot percentage as an encryption channel, setting screening parameters for 4 channels for screening respectively to obtain an encryption channel halftone picture consisting of screen dots and 3 common channel halftone pictures, wherein the rest channels are 3 common channels;
the screening processing adopts a half-tone screen, the screening parameters comprise output resolution, screening line number and mesh point shape, when the screening processing is respectively carried out on the 4 channels, the same output resolution, screening line number and mesh point shape are adopted, and the output resolution is integral multiple of the screening line number; the shapes of the net points are all round; recording the number of the screening lines as l, and the screening parameters also comprise a screening angle, and recording the screening angle of the encryption channel as theta; the screening angles comprise 0 degree, 18.44 degrees, 45 degrees and 71.57 degrees, theta is 0 degree, and the screening angles of the 3 common channels are any combination of 18.44 degrees, 45 degrees and 71.57 degrees;
step two, hiding the anti-counterfeiting information
(1) And dot displacement: recording areas corresponding to the areas with the same screen dot percentage in the encryption channel halftone graph as encryption areas; selecting anti-counterfeiting information to be hidden, establishing a mesh point selection area in the encryption area according to the profile of the anti-counterfeiting information, recording mesh points in the mesh point selection area as a set A, displacing mesh points of the set A in a vertically upward or vertically downward direction by a displacement distance S, and performing a displacement algorithm:
(2) and image synthesis: after the dot displacement is finished, obtaining a coded encryption channel halftone image, and synthesizing the coded encryption channel halftone image and 3 common channel halftone images to obtain an original halftone image carrying anti-counterfeiting information, so as to finish the hiding of the anti-counterfeiting information; the image synthesis method comprises the following steps:
newly building an image I in the photoshop, wherein the length and the width of the image I are the same as those of the original, the resolution of the image I is the same as the output resolution, the background content is white, the color mode is a CMKY mode, and copying the encoding encryption channel halftone map and the 3 common channel halftone maps into corresponding color channels to obtain the encoding encryption channel halftone map;
step three, extracting anti-counterfeiting information
Preparing a digital file type decoding linear grating, wherein the area of the decoding linear grating is larger than that of the encryption region, the decoding linear grating is composed of black stripes and transparent stripes which are same in length and arranged in parallel at intervals, and the width of each black stripe is T1The width of the transparent stripe is T2，The T is1The calculation method comprises the following steps:
in the image processing software, T is obtained according to calculation1And T2And (3) making to obtain a decoding linear grating, covering the decoding linear grating on the original halftone image, rotating and moving the decoding linear grating for extraction until the anti-counterfeiting information is observed, and finishing the extraction of the anti-counterfeiting information.
2. The linear grating matching method based on dot percentage and screening number of claim 1, wherein: in the second step, the displacement algorithm is as follows:
3. the linear grating matching method based on dot percentage and screening number of claim 1, wherein: in the third step, T1The calculation method comprises the following steps:
4. the linear grating matching method based on dot percentage and screening number of claim 1, wherein: in the first step, the original document is a digital file opened by adopting photoshop software, the screening processing adopts a half-tone screen in photoshop, and the method for screening each channel comprises the following steps: and selecting a channel, converting the channel into a bitmap, setting the output resolution during conversion, and then screening the channel by adopting a half-tone screen.
5. The linear grating matching method based on dot percentage and screening number of claim 4, wherein: the number of the screened lines is 96lpi, and the output resolution is 2400 dpi.
6. The linear grating matching method based on dot percentage and screening number of claim 1, wherein: in the second step, the dot displacement further comprises dot percentage improvement, and then image synthesis is performed, wherein the dot percentage improvement method comprises the following steps:
recording a set of the net points on the boundary of the net point selection area in the set A as B, wherein B belongs to A, recording a set of the net points which are outside the net point selection area and are closest to the net point selection area in the encryption channel as G, and adapting the outline formed by the net points in the set G to the outline formed by the net points in the set B; when the mesh point displacement is carried out, the motion states of the mesh points of the set B relative to the mesh points of the set G comprise far motion, close motion and parallel motion; the set of net points of the approach motion is B1The set of dots of the far motion is B2After the dot displacement is finished, the set B is processed1The screen dot percentage of the screen dot is improved, and the improved screen dot percentage is α1'：
Then to the collectionAnd B2The screen dot percentage of the screen dot is improved, and the improved screen dot percentage is α2'：
Set B2After the dot percentage improvement is completed, copy set B2To obtain a set B2', and will set B2' mesh points in move to set B2And the halftone image of the coding encryption channel is obtained between the halftone dots corresponding to the set G.
7. The linear grating matching method based on dot percentage and screening number of claim 1, wherein: the anti-counterfeiting information is characters and/or graphs.
8. The linear grating matching method based on dot percentage and screening number of claim 7, wherein: the anti-counterfeiting information is characters, the website displacement is completed by adopting photoshop software, and the method for establishing the website selection area comprises the following steps:
(1) newly building an image II in the photoshop, wherein the length and the width of the image II are the same as those of the original, the resolution of the image II is the same as the output resolution, the background content is white, obtaining 'layer 0' in a layer channel, copying the encryption channel halftone map into the image II to obtain 'layer 1', copying 'layer 1' to obtain 'layer 2'; arranging the layer 2, the layer 1 and the layer 0 in the layer window in sequence;
(2) selecting a character tool, inputting anti-counterfeiting information to obtain a layer 3, selecting the anti-counterfeiting information by using a magic stick tool to obtain a dot selection area, and setting the layer 3 to be invisible.
9. The linear grating matching method based on dot percentage and screening number of claim 7, wherein: the anti-counterfeiting information is a graph, the website displacement is completed by adopting photoshop software, and the method for establishing the website selection area comprises the following steps:
(1) newly building an image III in the photoshop, wherein the length and the width of the image III are the same as those of the original, the resolution of the image III is the same as the output resolution, the background content is white, obtaining 'layer 0' in a layer channel, copying the encryption channel halftone map into the image III to obtain 'layer 1', copying 'layer 1' to obtain 'layer 2'; arranging the layer 2, the layer 1 and the layer 0 in the layer window in sequence;
(2) and putting anti-counterfeiting information to obtain a 'layer 3', selecting the anti-counterfeiting information by using a magic stick tool to obtain a dot selection area, and setting the 'layer 3' to be invisible.
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20060170974A1 (en) * | 2005-01-28 | 2006-08-03 | Hsi-Chun Wang | Method of watermark with hybrid halftone dots |
| CN103996166A (en) * | 2014-06-05 | 2014-08-20 | 上海理工大学 | Holographic anti-counterfeiting algorithm based on shape of screen dot |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20060170974A1 (en) * | 2005-01-28 | 2006-08-03 | Hsi-Chun Wang | Method of watermark with hybrid halftone dots |
| CN103996166A (en) * | 2014-06-05 | 2014-08-20 | 上海理工大学 | Holographic anti-counterfeiting algorithm based on shape of screen dot |
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