Method for generating a data-bearing halftone image, and method for decoding the data-bearing halftone image

Patent metadata

Field	Value
Publication number	US-2017109857-A1
Application number	US-201615147923-A
Country	US
Kind code	A1
Filing date	May 6, 2016
Priority date	Oct 16, 2015
Publication date	Apr 20, 2017
Grant date	—

Abstract

A method for generating a data-bearing image is implemented by an encoding system including a halftoning module and an encoding module that stores encoding rules associated with respective codes. In the method, the halftoning module converts a grayscale image into a halftone image having a plurality of image cells each consisting of a plurality of dots, at least one of which is a first-tone dot and each of the rest of which is a second-tone dot. Afterward, the encoding module generates a data-bearing halftone image encoded with at least one of the codes by maintaining or changing the number of the first-tone dots in one of the image cells based on one of the encoding rules associated with the at least one of the codes.

First claim

What is claimed is:

1 . A method for generating a data-bearing halftone image, the method to be implemented by an encoding system that includes a halftoning module and an encoding module that stores a plurality of encoding rules associated with respective codes therein, the method comprising the steps of:
converting, by the halftoning module, a grayscale image into a halftone image by screening the grayscale image using a predetermined threshold matrix that includes a plurality of grayscale threshold values, the halftone image having a plurality of image cells each corresponding to the predetermined threshold matrix in size, each of the image cells consisting of a plurality of dots, at least one of which is a first-tone dot and each of the rest of which is a second-tone dot; and generating, by the encoding module, a data-bearing halftone image that is encoded with at least one of the codes by maintaining or changing the number of the first-tone dots in one of the image cells according to one of the encoding rules that is associated with the at least one of the codes.

2 . The method of claim 1 , the encoding module storing sixteen of the encoding rules associated respectively with sixteen four-bit codes, wherein generating the data-bearing halftone image includes:
defining at least one encodable block that includes adjacent four of the image cells of the halftone image; and encoding the at least one encodable block with one of the four-bit codes by performing an encoding action on each of the image cells included in the at least one encodable block according to one of the encoding rules that is associated with the one of the four-bit codes, the encoding action including one of increasing the number of the first-tone dots in the image cell by one, decreasing the number of the first-tone dots in the image cell by one, and maintaining the number of the first-tone dots in the image cell.

3 . The method of claim 1 , the encoding system further including an image optimization module, the method further comprising the step of performing image optimization on each of the image cells of the data-bearing halftone image by:
for each first-tone dot in the image cell, calculating a differential value between the image cell and a corresponding portion of the grayscale image; for each first-tone dot in the image cell, calculating a differential value between the corresponding portion of the grayscale image and each of at least one candidate image cell that is obtained by swapping the first-tone dot with a corresponding second-tone dot adjacent to the first-tone dot within the image cell; determining a lowest one of the differential values thus calculated; and replacing the image cell with one of the image cell and the candidate image cell(s) that has the lowest differential value.

4 . The method of claim 3 , wherein the image optimization is performed for each of the image cells in an order from left to right and from top to bottom.

5 . The method of claim 1 , wherein the predetermined threshold matrix is a square matrix having a screen tile vector set composed of two two-dimensional vectors [0, m] and [m, 0], and has m×m grayscale threshold values.

6 . The method of claim 5 , wherein the grayscale threshold values in the threshold matrix are generated using one of clustered-dot ordered dithering and dispersed-dot ordered dithering.

7 . The method of claim 1 , wherein:
in increasing the number of the first-tone dots in the image cell by one, one of the second-tone dots is randomly selected and converted into a first-tone dot; and in decreasing the number of the first-tone dots in the image cell by one, one of the first-tone dots is randomly selected and converted into a second-tone dot.

8 . A method for decoding a data-bearing halftone image, the data-bearing halftone image being encoded with a code and including a plurality of image cells, each of image cells consisting of a plurality of dots, at least one of which is a first-tone dot and each of the rest of which is a second-tone dot, the method being implemented by a decoding system including a database, a halftoning module and a decoding module, the database storing therein a grayscale image that corresponds to the data-bearing halftone image, a predetermined threshold matrix that includes a plurality of grayscale threshold values, and a plurality of encoding rules associated with respective codes, the method comprising:
converting, by the halftoning module, the grayscale image into a halftone image by screening the grayscale image using the predetermined threshold matrix, the halftone image having a plurality of image cells each corresponding to the predetermined threshold matrix in size; and decoding, by the decoding module, a data-bearing block of the data-bearing halftone image by
identifying the data-bearing block of the data-bearing halftone image that corresponds in location to an encodable block in the halftone image, the data-bearing block including adjacent four of the image cells of the data-bearing halftone image,
determining, between each of the image cells in the encodable block of the halftone image and a corresponding one of the image cells in the data-bearing block of the data-bearing halftone image, a difference of a number of first-tone dots contained therein, and
determining the code represented by the data-bearing block of the data-bearing halftone image based on the plurality of sets of encoding rules, and on the difference of the number of first-tone dots between each of the image cells in the encodable block of the halftone image and corresponding one of the image cells in the data-bearing block of the data-bearing halftone image.

9 . The method of claim 8 , wherein the predetermined threshold matrix is a square matrix having a screen tile vector set composed of two two-dimensional vectors [0,m] and [m,0], and has m*m grayscale threshold values.

10 . The method of claim 9 , wherein the grayscale threshold values in the threshold matrix are generated using one of clustered-dot ordered dithering and dispersed-dot ordered dithering.

Assignees

• Univ Nat Taipei Technology

Inventors

• Chen Yung-Yao
• Chi Kuan-Yu
• Chen Po-Han
• Chen Wei-Sheng
• Chen Kai-Wen

Classifications

• G06T2201/0061

  Embedding of the watermark in each block of the image, e.g. segmented watermarking · CPC title

• H04N1/32256

  in halftone data · CPC title

• G06T1/0028 Primary

  Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking · CPC title

• H04N1/4051

  producing a dispersed dots halftone pattern, the dots having substantially the same size (different sizes H04N1/4057) · CPC title

• G06T1/0021 Primary

  Image watermarking · CPC title