18-03-2014, 01:00 PM
Generic Lossless Visible Watermarking-A New Approach
INTRODUCTION
The advance of computer technologies and the proliferation of the Internet have made reproduction and distribution of digital information easier than ever before. Copyright protection of intellectual properties has, therefore, become an important topic. One way for copyright protection is digital watermarking [1]-[7], which mean embedding of certain specific information about the copyright holder (company logos, ownership descriptions, etc.) into the media to be protected. Digital watermarking methods for images are usually categorized into two types: invisible and visible.
The first type aims to embed copyright information imperceptibly into host media such that in cases of copyright infringements, the hidden information can be retrieved to identify the ownership of the protected host. It is important for the watermarked image to be resistant to common image operations to ensure that the hidden information is still retrievable after such alterations. Methods of the second type, on the other hand, yield visible watermarks which are generally clearly visible after common image operations are applied. In addition, visible watermarks convey ownership information directly on the media and can deter attempts of copyright violations. Embedding of watermarks, either visible or invisible, degrade the quality of the host media in general.
LITERATURE SURVEY
The first watermark ever put on personal property is still under debate, but it is believed to have begun in Bologna, Italy in 1282. It was found on a piece of paper, and although the purpose of it is still under debate as well, there are many that believe watermarks were used for similar reasons they are used for today. Some even speculate that certain watermarks “were used by mystical groups to carry signals with hidden meanings,” somewhat similar to what they are used for today . Today watermarks can be visible, seen by the human eye, or invisible, only detectable by computer software. Over the past few years, there has been tremendous growth in computer networks and more specifically, the World Wide Web. This phenomenon, coupled with the exponential increase of computer performance, has facilitated the distribution of multimedia data such as images. Publishers, artists, and photographers, however, may be unwilling to distribute pictures over the Internet due to a lack of security; images can be easily duplicated and distributed without the owner’s consent. Digital watermarks have been proposed as a way to tackle this tough issue. This digital signature could discourage copyright violation, and may help determine the authenticity and ownership of an image.
WATERMARK CLASSIFICATION
There are several criteria how watermarks for images or video sequences can be classified. Watermarking techniques can be classified into spatial or frequency domain by place of application. Spatial domain watermarking is performed by modifying values of pixel color samples of a video frame whereas watermarks of frequency domain techniques are applied to coefficients obtained as the result of a frequency transform of either a whole frame or single block-shaped regions of a frame. Discrete Fourier Transform and Discrete Wavelet Transform belong among whole-frame frequency transforms. The representative of the block frequency transform is Discrete Cosine Transform. Classification into these groups is according to the way how the transforms are usually used in practice.
CHARACTERISTICS OF WATERMARKS
Imperceptibility
The watermark must be invisible with the human eye. It is necessary to take into account to the maximum model HVS (Human Visual System). Let us take two very
simple examples to stress its importance. Let us imagine an image in level of gray with
a broad uniform zone. If one adds a little noise, this immediately will be seen in this
zone. It is rather necessary to put the watermark in zones of strong gradient (edges of
forms, strongly textured zones) where the eye is less sensitive. Another example
comes from the watermarking of the images colors. It is known that the human eye is not sensitive in the same way to all the wavelengths. One can thus more or less dissimulate information according to the color considered.
Robustness
We could separate this heading in two parts: “the robustness and the security”.
These two characteristics are often confused especially in the case of the watermarking.
Usually, robustness is used to define the resistance of the watermarking vis-a-vis
transformations of the watermarked image. These transformations can be of geometrical
type (rotation, zoom, cropping). They can modify certain characteristics of the image
(histogram of the colors, saturation). They can also be all the types of frequential
degradations of the image (lossy compression, high pass filters or low pass filter,
analogical->numérique->analogique passage, impression of the image, etc).
WATERMARKING APPLICATIONS
There are two main applications of watermarking, copyright protection and information hiding. For the area of copyright protection, the user can unambiguously identify themselves as the owner of the image (video, audio etc.) For information hiding, data can be hidden in a seemingly normal image and the image transmitted. The data can then be extracted at the other end, assuming that the user at the other end has the relevant information to do so. In this section, we describe seven applications of the watermarking techniques. In order to fully understand the main challenges involved in the development of
watermarking-related tools, some applications of invisible watermarks are listed hereto.
CONCLUSION AND FUTURE WORK
In this paper, a new method for reversible visible watermarking with lossless image recovery capability has been proposed. The method uses one-to-one compound mappings that can map image pixel values to those of the desired visible watermarks. Relevant lemmas and theorems are described and proved to demonstrate the reversibility of the compound mappings for lossless reversible visible watermarking. The compound mappings allow different types of visible watermarks to be embedded, and two applications have been described for embedding opaque monochrome watermarks as well as translucent full-color ones.