TWI543588B - Data-bearing encoding system and decoding system utilizing black and white pixel swap modulation - Google Patents

Description

Halftone data steganography coding system and decoding system using pixel black and white interchange modulation

The invention relates to a data encoding method, in particular to a halftone data steganography coding system and a decoding system for hiding data in a halftone pattern by pixel black and white interchange.

In order not to damage the overall beauty of the printed matter, the industry has been developing how to hide product information, such as anti-counterfeiting materials, in printed matter, such as trademark patterns or pictures, so that it can be integrated with printed content. For example, as shown in FIG. 1, U.S. Patent No. 8,854,453 discloses a method of encoding in a halftone image, which displays a dot shape of a halftone unit 502 composed of a plurality of pixels, and by moving the dots up and down. , left and right upside down, so that the ink dot position can have four changes, so that the halftone units 502, 504, 506, 508 having four different ink dot positions respectively represent a two-bit coded material, for example, 00, 01 , 10, 11, by which information can be steganized in half-tone images in a two-bit encoding without affecting the overall beauty of the image. But this coding method is deliberate The way of moving the ink dots is contrary to the conventional halftone conversion method, and the position of the ink dots is greatly changed, which tends to deteriorate the quality of the original halftone image.

In addition, a direct binary search (hereinafter referred to as DBS) can optimize the quality of a halftone image, as shown in FIG. 2, that is, test each pixel in a halftone image. For example, after the pixel 10 located at the center of FIG. 2 is swapped by black and white or by swapping with the neighboring eight adjacent pixels, the halftone image and the original grayscale image are both passed through a human visual model (simulation). The visual perception of the human eye (ie, comparing the differences between the two) produces a perceptual error value, and continuously repeats the above DBS steps to recursively adjust the halftone image until the perceptual error value produced by the human visual model no longer changes. That is, the error between the halftone image and the original grayscale image has been minimized, and then the above action is repeated on the next pixel until all the pixels complete the DBS, thereby making the halftone image through the direct binary search Visually closest to the original grayscale image.

Therefore, how to reduce the influence on the halftone image quality in the halftone image encoding process, and to combine the DBS technology to optimize the quality of the encoded halftone image, has become the focus of the present invention.

Accordingly, it is an object of the present invention to provide a halftone data steganography system and decoding system that utilizes pixel black and white interchange modulation to maintain halftone image quality.

Accordingly, the present invention utilizes a halftone data steganography system for pixel black and white interchange modulation to convert a grayscale image into a halftone image and to lie data in the halftone image; the system includes: halftone a conversion module that converts the grayscale image into a halftone image having a plurality of halftone cells according to a mxm square threshold matrix, and each of the halftone cells has mxm pixels, wherein m is a positive integer greater than two And an encoding module for loading a data into the halftone units of the halftone image, and determining that the data is a first data, the halftone to be loaded into the first data When the number of ink points of the unit remains unchanged, and when the data is judged to be a second data, a pixel is randomly selected from the halftone unit to be loaded into the second data, and when the pixel is determined to be an ink dot, The pixel is replaced with a non-ink dot, otherwise the pixel is replaced with an ink dot, so that the halftone cell becomes a coded unit that implies the data, and the halftone image is a coded halftone image.

In an embodiment of the invention, the halftone data steganography system using pixel black and white interchange modulation further includes an image optimization module for directly performing the halftone units in the encoded halftone image. Two-bit search, and perform direct binary search for only one halftone unit at a time, the direct binary search determines that one dot in the halftone unit is located in the middle, corner or side of the halftone unit And attempting to swap the ink dot with its adjacent non-ink dot pixel position until it is determined that one of the interchange results causes the halftone cell to be closest to a portion of the image corresponding to the grayscale image, that is, accepting the interchange result, and then The next ink dot repeats the direct two digits Meta-search, until all the dots complete the direct binary search, the image optimization module will perform the direct binary search for the next halftone unit, and the same in the encoded halftone image The halftone unit performs the direct binary search one by one from top to bottom and left to right, thereby generating an optimized encoded halftone image.

In an embodiment of the invention, the mxm square threshold matrix comprises a screen vector consisting of two two-dimensional vectors [m, 0], [0, m] and mxm threshold values.

In an embodiment of the invention, the threshold values are generated by a centralized dithering method or a decentralized dithering method.

In an embodiment of the invention, the first data is a binary number 0 and the second data is a binary number 1.

Furthermore, the present invention utilizes a halftone data steganography decoding system for pixel black and white interchange modulation to read data steganized in a coded halftone image, and includes: a database, the record and the coded halftone An original grayscale image corresponding to the image and a mxm square critical value matrix, and a data amount steganized in the encoded halftone image; a halftone conversion module, which is based on the mxm square critical value matrix Converting the image into a halftone image; and a decoding module, based on the amount of data, comparing the coded cells in the encoded halftone image to the halftone cells corresponding to the halftone image, and Determining the steganography of the coded unit when the number of ink points in the coded unit and the corresponding halftone unit are the same The data is a first data, and when the number of ink points in the coded unit and the corresponding halftone unit is different, it is determined that the data steganized in the coded unit is a second data.

In an embodiment of the invention, the mxm square threshold matrix comprises a screen vector consisting of two two-dimensional vectors [m, 0], [0, m] and mxm threshold values.

In an embodiment of the invention, the threshold values are generated by a centralized dithering method or a decentralized dithering method.

In an embodiment of the invention, the first data is a binary number 0, and the second data is a binary number 1

The effect of the present invention is that the present invention writes the first data into the halftone unit without changing the number of dots in the halftone unit, and changes the hue of a pixel randomly selected from the halftone sheet (black and white) Interchange), the second data is written into the halftone unit to not significantly change the position and number of ink dots in the halftone image during the encoding process. And by randomly selecting a pixel from the halftone unit and changing the color tone thereof, the pixels that change the color tone can be evenly distributed in the encoded halftone image, so that the quality of the encoded halftone image is not affected; The image optimization module performs a direct binary search for each halftone unit in a pair of coded halftone images from top to bottom and left to right in a halftone unit. Optimize the encoded halftone image and reduce the number of direct binary search executions Increase the speed of image processing.

1‧‧‧ halftone conversion module

2‧‧‧Code Module

3‧‧‧Image to be encoded

3’‧‧‧ Coded imagery

4‧‧‧Image Optimization Module

30‧‧‧ Grayscale imagery

31‧‧‧ halftone image

32‧‧‧Coded image

33‧‧‧Optimized coded imagery

40‧‧‧square threshold matrix

51‧‧‧Database

52‧‧‧ halftone conversion module

53‧‧‧Decoding module

301‧‧‧ Block

311‧‧‧ halftone unit

312‧‧‧Coded unit

Other features and effects of the present invention will be apparent from the following description of the drawings, wherein: FIG. 1 is a schematic diagram of a conventional halftone image encoding method for encoding by moving a dot shape; A schematic diagram of a direct binary search method is shown; FIG. 3 is a schematic diagram showing the components of an embodiment of the halftone data steganography system using pixel black and white interchange modulation; FIG. 4 illustrates the halftone conversion mode of the embodiment. The method of converting a grayscale image into a halftone image; FIG. 5 illustrates that the encoding module of the embodiment steganates data in a halftone unit; FIG. 6 illustrates that an encoded halftone image is optimized by the image of the embodiment. The module is processed to become an optimized coded halftone image; FIG. 7 illustrates that the image optimization module of the embodiment first determines that the ink dot is located in the middle, corner or side of the halftone unit when performing direct binary search. 8 is a schematic diagram showing the components of an embodiment of a halftone data steganography decoding system using pixel black and white interchange modulation; and FIG. 9 illustrates the database record of FIG. An original grayscale image and a square threshold matrix, and the decoding module compares the relative positions in the halftone image and the encoded halftone image The halftone unit is decoded to obtain data that is steganized in the encoded halftone image.

Before the present invention is described in detail, it should be noted that in the following description, similar elements are denoted by the same reference numerals.

Referring to FIG. 3, an embodiment of a halftone data rewritable coding system using pixel black and white interchange modulation is used to convert a grayscale image into a halftone image and rewrit the data in the halftone image. . The system includes a halftone conversion module 1 and an encoding module 2. The grayscale image 30 is an example of an image having 16×16 pixels, which represents a small portion of a to-be-coded image 3. The halftone conversion module 1 converts the grayscale image 30 into a halftone image 31 according to a square threshold matrix 40.

Halftone is a method commonly used in the printing industry to process tone and simulate continuous tone. The images printed on the printer can only be represented by the two tones of ink or no ink. The binary image like this is called halftone image. Therefore, by adjusting the arrangement of the ink dots on the printing plane, the principle of "visual integration" of the human eye can be utilized, so that the halftone image reproduces the feeling of continuously adjusting the image under a certain distance observation. So halftone technology is a technique for converting continuously tuned images into halftone images. The halftone screen method (also known as ordered dithering method) first divides a continuous tone image (grayscale image) into a plurality of blocks of the same size as a threshold matrix, and then sets their grayscale values. a critical relationship with the relative position in the critical matrix The value is compared, if the gray level value of the relative position is greater than the critical value, the white point is output (no ink), and vice versa, the black point (inking) is output, thereby converting the continuous tone image into a halftone image.

When the halftone screen method is used, the arrangement and shape of the dots of the generated halftone image are affected by the order of the critical values in the critical matrix. Therefore, the conventional threshold matrix can be mainly classified into two types: the Clustered-Dot Ordered Dithering method and the Dispersed-Dot Ordered Dithering method, as shown in the following two figures.

In addition, when using the halftone screen method, there are two factors that affect the threshold matrix. The first one is the order of the critical values in the matrix, such as the aforementioned "concentrated dithering method" and "distributed dithering". Color method." The second is the Screen Tile Vector, which determines the shape and rotation angle of the threshold matrix. The screen vector contains two two-dimensional vectors n ₁ , n ₂ , and the two two-dimensional vectors n ₁ , n ₂ determine the number of pixels in each halftone cell in the halftone image (below Will be further explained). Since the "threshold matrix" is a conventional technique applied to the traditional halftone screen method, and is not the focus of this discussion, it will not be described in detail here. For related technologies, see "Design of Color Screen Tile Vector Sets" and "Computer-aided design of clustered-dot color screens based on a human visual system model" and other papers.

Therefore, in the present embodiment, as shown in FIG. 4, the square threshold matrix 40 employed is a 4x4 distributed threshold matrix, which is composed of two two-dimensional vectors [4, 0], [0, 4] A screen vector composed of a matrix consisting of 4x4 thresholds. Of course, this embodiment can also adopt a centralized threshold matrix.

Therefore, as shown in FIG. 4, the halftone conversion module 1 divides the grayscale image 30 into 16 blocks 301 in units of 4×4 pixels according to the size of the square threshold matrix 40, and then from top to bottom. From left to right, the grayscale value of the 4x4 pixels of each block 301 is compared with the critical value of the relative position in the threshold matrix 40. If the grayscale value of the pixel is greater than the critical value, the output 1 represents white, otherwise The output 0 represents black (ink dot), whereby the grayscale image 30 is converted into a halftone image 31 displayed only in black and white, the halftone image 31 includes a plurality of halftone units 311, and each halftone unit 311 Has 4x4 pixels.

Then, the halftone image 31 is input to the encoding module 2, and the encoding module 2 treats each halftone unit 311 of the halftone image 31 as a codeable unit, and each of the codeable units can write one bit. Therefore, as shown in FIG. 5, if the encoding module 2 is to steble the binary four-bit data 0110 in the four consecutive halftone units 311 of the halftone image 31, the encoding rule is as follows. First, the encoding module 2 determines that the first bit is a first data, for example, the number 0, so that the figure 5 is to be loaded. The number of dots of the first halftone unit 311 of the first material (i.e., 0) remains unchanged, causing the first halftone unit 311 to become an encoded unit 312 that implies the first bit material (i.e., 0). . Next, the encoding module 2 determines that the second bit is a second data. For example, when the number 1 is 1, a pixel is randomly selected from the second halftone unit 311 to be loaded into the second data (ie, 1). For example, the pixel indicated by the thick frame in FIG. 5, and determine whether the pixel is an ink dot, and if so, the pixel is replaced with a non-ink point (white point), otherwise the pixel is replaced with an ink dot, thereby The two bit data (i.e., 1) is steganized in the second halftone unit 311, causing the halftone unit 311 to become an encoded unit 312 that implies the second bit. Then, the encoding module 2 sequentially dictates the third bit (1) and the fourth bit (0) in the third and fourth halftone units 311 according to the above encoding rule, thereby making the halftone image 31 becomes a coded halftone image 32 as shown in FIG. It is worth mentioning that the above first information can also be the number 1, and the second information is the number 0.

Therefore, as can be seen from the above description, each halftone unit 311 in the halftone image 32 can write the data of one bit, so that one halftone image 32 (depending on the number of halftone units it contains) can be hidden. Write a lot of information in it. And the present embodiment writes the first material into the halftone unit 311 by changing the number of ink dots in the halftone unit 311, and by changing the color tone of a pixel randomly selected from the halftone unit 311, The second data is written into the halftone unit 311, and the position and the number of the ink dots in the halftone image 31 can be avoided as much as possible during the encoding process, especially when the first data written is more than the second data, so during the encoding process. Will not change the half color greatly Adjust the position of the ink dots in the image. Moreover, by randomly selecting a pixel from the halftone unit 311 and changing the color tone thereof, the pixels which change the color tone can be evenly distributed in the encoded halftone image 32, so that even some pixels in the encoded halftone image 32 are Changing the color tone does not affect its image quality.

Moreover, in order to make the encoded halftone image 32 have better image quality, as shown in FIG. 6, the embodiment further includes an image optimization module 4 for the halftones in the encoded halftone image 32. The unit 311 (including the coded unit 312) performs a direct binary search (hereinafter referred to as DBS), and the image optimization module 4 of the embodiment performs DBS on only one halftone unit 311 at a time, for example, FIG. It is shown that the direct binary search first judges that one dot in the halftone unit 311 is located in the middle of the halftone unit 311 (as shown by 7A in FIG. 7) and a corner (as shown by 7B in FIG. 7). Or the side (as shown by 7C in Fig. 7), and let the ink dot be only one of the non-ink dots adjacent to its surroundings (shown by the dashed box in 7A, 7B, 7C in Fig. 7) (ie, White point) pixel interchange, and then the halftone unit 311 after the interchangeable pixel and the corresponding partial image in the original gray scale image are perceived by a human visual system filter kernel (ie, a human visual system filter kernel) (ie, Comparing the differences between the two) produces a perceptual error value and continually repeats the above steps (ie, The ink dots are respectively interchanged with another non-ink point (ie, white point) pixel adjacent to the periphery thereof, and the perceptual error value is continuously generated through the human eye vision model until one of the interchange results is found to minimize the perceptual error value and no longer change. The human visual model determines the halftone unit 311 and the original grayscale image. The error of the corresponding partial image has been minimized, that is, the halftone unit 311 is determined to be closest to the corresponding partial image in the original grayscale image, and the result of the interchange is accepted. Then, DBS is repeatedly executed on the next ink dot in the halftone unit 311 until all the ink dots in the halftone unit 311 complete the DBS, and then the DBS is performed on the next halftone unit 311, thereby generating An encoded halftone image 33 is optimized. Because the above DBS is a conventional technology, and is not the focus of this case, it will not be described in detail here. For related technologies, refer to the paper "A Novel Barcode System for Intelligent Automation Industry".

Therefore, since the direct binary search (DBS) performed by the image optimization module 4 of the present embodiment causes only the ink dots in the halftone unit 311 to change its position (SWAP) in the halftone unit 311, each The number of dots in one halftone unit 311 can remain unchanged while retaining the encoded material implied therein.

In addition, since the image optimization module 4 of the present embodiment performs a direct binary search by using each of the halftone units 311 in the pair of coded halftone images 32 from top to bottom and left to right. Therefore, the image optimization module 4 performs a direct binary search on a halftone unit 311 until the error of the halftone unit 311 and the corresponding partial image in the original grayscale image converges to a minimum. The next halftone unit 311 performs a direct binary search, thereby reducing the number of direct binary search executions and increasing the speed of image processing.

So, when a pattern or trademark is a coded halftone image, for example When the optimized half-coded halftone image 33 is presented as described above, in order to read the data steered in the optimized halftone image 33 for subsequent verification or application, as shown in FIG. 8, the present invention utilizes pixel black and white interchange modulation. An embodiment of the halftone data steganographic decoding system for extracting data steganized in the optimized encoded halftone image 33, and mainly comprising a database 51, a halftone conversion module 52 and a decoding module Group 53. As shown in Fig. 9, the optimized encoded halftone image 33 represents a portion of the image of an encoded image 3'. The database 51 mainly records the original grayscale image 3 (represented by the partial grayscale image 30 in the figure) corresponding to the encoded image 3' (indicated by the optimized encoded halftone image 33), and is used to set the grayscale The image 30 is converted into a square threshold matrix 40 of halftone images 31.

Therefore, as shown in FIG. 8 and FIG. 9, when the decoding module 53 receives the optimized halftone image 33, it notifies the halftone conversion module 52, and the halftone conversion module 52 is taken out from the database 51. The original grayscale image 30 corresponding to the optimized coded halftone image 33, and the original grayscale image 30 is converted into the halftone image 31 according to the square threshold matrix 40, as in the foregoing halftone conversion module 1. Provided to the decoding module 53.

Then, as shown in FIG. 9, the decoding module 53 sequentially compares the number of ink dots of the halftone unit 311 corresponding to the position in the encoded unit 312 and the halftone image 31 in the encoded halftone image 33, for example, for example. 9, the number of ink dots in the first encoded unit 312 and the ink dots in the corresponding halftone unit 311 in the halftone image 31 are shown in FIG. If the number is the same, the decoding module 53 determines that the material steganized in the first encoded unit 312 is the first data (ie, 0), and then the decoding module 53 compares the number of ink points in the second encoded unit 312. If the number of ink dots in the corresponding halftone unit 311 in the halftone image 31 is different, it is determined that the data hidden in the second encoded unit 312 is the second data (ie, 1), so According to the above decoding rule, the decoding module 53 may determine that the data steganized in the third encoded unit 312 is the second data (ie, 1), and the data steganized in the fourth encoded unit 312 is the first data. (i.e., 0), whereby the steganized material 0110 can be taken out from the optimized encoded halftone image 33.

In summary, the present invention writes the first material into the halftone unit 311 by changing the number of ink dots in the halftone unit 311, and changes the color tone of a pixel randomly selected from the halftone unit 311. (Black-and-white interchange), the second material is written in the halftone unit 311 so as not to largely change the position and number of ink dots in the halftone image 31 during the encoding process. And by randomly selecting a pixel from the halftone unit 311 and changing the color tone thereof, the pixels which change the color tone can be evenly distributed in the encoded halftone image 32, so that the quality of the encoded halftone image 32 is not affected. And directly performing, by the image optimization module 40, a halftone unit 311 in a pair of coded halftone images 32 in a top-to-bottom, left-to-right manner in a unit of one halftone unit 311. The two-bit search, in addition to optimizing the encoded halftone image 32, and reducing the number of direct binary search executions, while increasing the speed of image processing, does achieve the efficacy and purpose of the present invention.

However, the above is only the embodiment of the present invention, and the scope of the invention is not limited thereto, and all the equivalent equivalent changes and modifications according to the scope of the patent application and the patent specification of the present invention are still The scope of the invention is covered.

1‧‧‧ halftone conversion module

2‧‧‧Code Module

4‧‧‧Image Optimization Module

Claims (9)

A halftone data steganography system using pixel black and white interchange modulation for converting a grayscale image into a halftone image and rewriting data in the halftone image; the system comprises: a halftone conversion module Converting the grayscale image into a halftone image having a plurality of halftone cells according to a mxm square threshold matrix, and each of the halftone cells has mxm pixels, wherein m is a positive integer greater than 2; The encoding module is configured to load a data into the halftone units of the halftone image, and when the data is a first data, the ink of the halftone unit to be loaded into the first data is determined When the number of points remains unchanged, and the data is judged to be a second data, a pixel is randomly selected from the halftone unit to be loaded into the second data, and when the pixel is judged to be an ink dot, the pixel is changed A non-ink point is formed, otherwise the pixel is replaced with an ink dot, so that the halftone unit becomes a coded unit that implies the material, and the halftone image becomes a coded halftone image. The halftone data steganography coding system using pixel black and white interchange modulation according to claim 1, further comprising an image optimization module, wherein the halftone unit in the coded halftone image is directly two-digit Meta search, and perform direct binary search for only one halftone unit at a time, the direct binary search determines that one dot in the halftone unit is located in the middle, corner or side of the halftone unit, and Trying to swap the ink dot with its adjacent non-ink dot pixel position until it is determined that one of the interchange results causes the halftone cell to be connected to a portion of the image corresponding to the grayscale image. Nearly, the result of the exchange is accepted, and the direct binary search is repeated for the next ink dot until all the ink dots complete the direct binary search, and the image optimization module will be the next half. The tonal unit performs the direct binary search, and performs the direct binary search one by one from top to bottom and left to right for the halftone units in the encoded halftone image, thereby generating one of the most Optimize the encoded halftone image. A halftone data steganography system using pixel black and white interchange modulation according to claim 1 or 2, wherein the mxm square threshold matrix comprises two two-dimensional vectors of [m, 0], [0, m] A mesh vector constructed and mxm thresholds. A halftone data steganography system using pixel black and white interchange modulation as described in claim 3, wherein the threshold values are generated by a centralized dithering method or a decentralized dithering method. A halftone data steganography system using pixel black and white interchange modulation as claimed in claim 1, wherein the first data is a binary number 0, and the second data is a binary number 1. A halftone data steganography decoding system using pixel black and white interchange modulation for reading data steganized in a coded halftone image, and comprising: a database for recording a corresponding one of the encoded halftone images An original grayscale image and a mxm square threshold matrix, and a data amount steganized in the encoded halftone image; a halftone conversion module that converts the original grayscale image into a matrix based on the mxm square threshold matrix Halftone image; and a decoding module, based on the amount of data, comparing the encoded units in the encoded halftone image with the halftone units corresponding to the halftone image, and comparing the encoded units with the When the corresponding number of ink dots in the halftone unit is the same, determining that the material steganized in the encoded unit is a first data, and comparing the ink in the encoded unit and the corresponding halftone unit When the number of points is different, it is determined that the data steganized in the coded unit is a second data. The halftone data steganography decoding system using pixel black and white interchange modulation according to claim 6, wherein the mxm square critical value matrix comprises a two-dimensional vector composed of [m, 0], [0, m] A screen vector and mxm thresholds. A halftone data steganography decoding system using pixel black and white interchange modulation according to claim 7, wherein the threshold values are generated by a centralized dithering method or a decentralized dithering method. A halftone data steganography decoding system using pixel black and white interchange modulation as claimed in claim 7, wherein the first material is a binary number 0, and the second data is a binary number 1.