Color in Image Watermarking

Color in Image Watermarking

Gaël Chareyron (École Supérieure d’Ingénieurs Léonard de Vinci, France), Jérôme Da Rugna (École Supérieure d’Ingénieurs Léonard de Vinci, France) and Alain Trémeau (Laboratoire Hubert Curien, Université Jean Monnet, France)
DOI: 10.4018/978-1-61520-903-3.ch003
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This chapter summarizes the state-of-the-art color techniques used in the emerging field of image watermarking. It is now well understood that a color approach is required when it comes to deal with security, steganography and watermarking applications of multimedia contents. Indeed, consumers and business expectations are focused on the protection of their contents, which are here color images and videos. In the past few years, several gray-level image watermarking schemes have been proposed but their application to color image is often inadequate since they usually work with the luminance or with individual color channel. Unfortunately, color cannot be considered as a simple RGB decomposition and all of its intrinsic information must be integrated in the watermarking process. Therefore, it is the chapter objective to present, first, the major difficulties associated with the treatment of color images, and second, the state-of-the-art methods used in the field of color image watermarking.
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In the last decade, we have seen a tremendous growth in color and color-based applications within the signal, image and video processing communities. Color is no longer interpreted as an extension of gray scale and is now considered as a key element for a number of image and video processing systems. In particular, color space transforms have played a central role in coding, compression and transmission applications. Color also plays a major role in pattern recognition and digital multimedia, where color based-features and color segmentations have been proven effective in indexing and multimedia content access. Moreover, the fusion of color and edge based features has improved the performance of image retrieval applications. Furthermore, color has become more recently a major component in security, steganography, and watermarking applications of multimedia contents (Trémeau et al., 2008)

This chapter presents the state-of-the-art watermarking techniques that are specifically designed for color images. Watermarking algorithms are generally used for content origin identification, copy protection, illegal copies tracking, fingerprinting, and content access control (Elbasi & Eskicioglu, 2006; Lukac & Plataniotis, 2007). The main objective of the watermarking techniques is to embed data into a host image by introducing changes that are imperceptible to the human eye but recoverable by a computer program. The signature locations in the image are determined by a secret key that prevents possible attacks or alterations from:

  • Signal processing algorithms, like compression, coding transformations, contrast enhancement, color enhancement, dithering, re-sampling.

  • Geometrical transformations, such as rotation, translation, cropping, scaling.

  • Watermark removal, watermark duplication or unauthorized detection.

In general, watermarking algorithms are based either on an additive process, a multiplicative or a quantization process. The watermark is extracted from the marked image either blindly or with a secret key. Most of the watermarking schemes are symmetric (i.e. the embedding and detection keys are identical). While several methods have been proposed to watermark grey level images, only a few have been designed for color images. Most of the time, these methods integrate color information and human vision system by using histogram and quantization scheme, frequency domain transform or spatial domain processing. Recently, these approaches have clearly demonstrated that, for many demanding applications (High Definition video as example), reaching an invisible and robust mark requires, at least, the integration of the color information within the watermarking process. For these reasons, this chapter is divided in two parts. The first part is focused on the major difficulties associated with color treatment and the second part presents the state-of-the-art methods in use in the field of color image watermarking.


Color In Image Watermarking: Issues And Problems

Since the traditional color Red Green Blue (RGB) triplet has been proven successful in numerous applications, it is not surprising that the color information is processed in parallel for each color component independently of each other. Reducing the color information to three components is a simple abstraction that ignores the intrinsic information contained in the color. In particular, the Human Visual System and the inter-correlation between these colors components cannot be ignored (Sharma, 2002). Since the RGB values are the only data usually available, the goal of color imaging is to produce new algorithms that take into account the color definition and the color image formation. Furthermore, the transition from scalar to vector-valued image processing is not yet addressed in the watermarking literature and therefore it becomes essential to clarify first what is behind color information and what are the concepts associated with vector-valued color image processing.

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