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Grid-line watermarking: A novel method for creating a high-performance text-image watermark
(2013-01-01)
Yawai, Wiyada
;
Hiransakolwong, Nualsawat
This study aims to discover an effective method to watermark any text image in any language. The ultimate goal of this work is to generate invisible and more robust watermarks, increase the hiding capacity, and identify any change in the original text. Generally these are the limitations of most text-image watermarking methods. Using a grid of horizontal and vertical lines is one of the most effective methods to overcome these limitations. These grid lines run across textimage character-skeleton lines to finely mark and detect watermarks on these line-character intersection points; there is one intersection for one specific zero watermark pixel. Each intersection point is defined by one hiding bit of the watermark such that the more reference horizontal and vertical lines of grid pattern are plotted, the more points of intersection are obtained. This approach increases the hiding-bit capacity to watermark embedding, which is a disadvantage shared by many text-image watermarking methods. In addition, if all positions of all intersection points are collected, these points will act as the identity reference points of all original characters to verify their integrities after they are modified.
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Applying of the cross ratio to significant increase the watermark redundancy of a text image
(2012-10-16)
Yawai, Wiyada
;
Hiransakolwong, Nualsawat
The objective of this experiment was to apply the cross ratio theory to significantly increase the watermark data redundancy and integrity verification performance of a multi-language text image. Here, the cross ratio of four collinear points was applied to control the watermark em-bedding and detection processes by using the intersection positions of the horizontal (H) and vertical (V) and double (H & V) grid lines which virtually run across the text-character skeleton lines as the guidelines. Three layers of grid-line intersections were tested using multi-language text images including Thai, English, Chinese and Arabic. Our experi-ments revealed that three layers of three patterns of grid-line intersec-tions on each multi-language text image page, in which these grid lines were drawn and used to create multiple layers of intersection points for embedding secret data bits for watermarking effectively yielded a huge watermark hiding-bit redundancy. Nevertheless, when all points are embedded, it would be helpful for owners to be able verify their integrity.
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Increase the hiding-bit capacity and strength for text watermarking with the line intersection on text image
(2012-10-08)
Yawai, Wiyada
;
Hiransakolwong, Nualsawat
This research presents how to use the intersection position of horizontal line, virtually run across text character skeleton line on a text image under the cross ratio applying, to be the marking point of zero watermark; means watermarking without any actual watermark, which consequently increase the remarkable watermark hiding-bit capacity and robustness. One point of intersection across one text character skeleton line is one specific pixel which defined as one hiding-bit of zero watermark; just only marking its pattern, so that the more reference horizontal lines plotting, the more points of intersection would be got and increasing the hiding-bit capacity for watermarking which generally is the most limitation of other text watermarking methods. The high capacity for hiding bits means more chance to make many sets of redundant encrypted watermark data, in case some parts of text document image have been modified or tampered with. In addition, intersection points for virtually embedding watermarks still have a great strength for identifying the point of text which has been modified if all positions of intersection points are collected. Moreover, these intersection positions also has been applied with the cross ratio of four collinear points, to build up its robustness in order to survive from possibly attacking. The testing proved that this watermarking method can be effectively used to hide more redundant data, verify its integrity, be robust and easily apply it to multi-language text images such as English, Thai, Chinese and Arabic languages. © 2012 AICIT.
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Projective-invariant digital image watermarking technique using four co-planar feature points
(2005-12-01)
Chotikakamthorn, Nopporn
;
Pantuwong, Natapon
;
Yawai, Wiyada
The problem of digital image watermarking invariant to planar projective transformation is considered in this paper. Methods that are invariant to certain spatial transformations, such as 2D geometric, and a more general affine transformation, are now widely available. However, those methods fail if a possibly watermarked image has undergone a projective transformation. A method based on a well-known projective invariant property of triangle area ratios, constructed from a set of four co-planar feature points, is described in this paper. The proposed method makes use of such invariant property to compute watermark embedding locations. Formation of the required four feature points for such computation is described. Experimental results are shown to demonstrate failure of an existing affine-invariant watermarking method even at very small projective distortion, as well as the success of the proposed method in withstanding distortion due to the same transformation over wide projection angles. © 2005 IEEE.
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Digital watermarking technique for projective-distorted images using collinear points
(2005-01-01)
Pantuwong, Natapon
;
Yawai, Wiyada
;
Chotikakamthorn, Nopporn
Detection of a digital watermark in images distorted by geometric transforms is made difficult by the so-called synchronization problem. Many watermarking methods have been developed to be robust against an affine transform. Based on such assumption, those methods fail under a more general projective transform. In this paper, a method that is invariant to planar projective transform is presented. The method is based on a projective invariance property of the cross-ratio of four collinear points. Based on four coplanar points as obtained by extracting feature points from the host image, two sets of three collinear points are obtained. From each set of three collinear points, each watermark embedding location can be obtained through its cross-ratio relationship with those aforementioned three collinear points. A method to increase the number of embedding points in addition to those primarily derived from these sets of collinear points is also proposed. An algorithm to form a set of four coplanar points from feature points is also described.

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