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Abstract the rapid growth in the demand and consumption of the digital multimedia content in the past decade has led to some valid concerns over issues such as content security, authenticity, and digital rights management. Multimedia data hiding is defined as imperceptible embedding of information into a multimedia host. It provides potential solutions such as one used in satellite and medical applications and military which is called reversible data hiding. Reversibility allows original media to be completely recovered from marked media without distortion after embedded message has been extracted. Toward this direction, this thesis presents two proposed reversible data hiding methods. In the first proposed method, a reversible data embedding method that hides data through images in the spatial domain is proposed. Though the proposed reversible data embedding method distorts the original image to embed data into the image, the method restores the original image as well as extracts hidden data from the image in which the data are embedded. To guarantee the losslessness of data embedding, all pixel values after embedding must be in the dynamic range of pixels. Because the proposed method modifies some pixels to embed data and leaves other pixels as their original values in the spatial domain, it can easily keep all pixel values after embedding in the dynamic range of pixels. Thus, both the capacity and the image quality of generated images are simultaneously improved. Moreover, the proposed reversible data embedding method uses three embedding parameters based on the statistics of pixel blocks to embed and extract data. By using these embedding parameters, this method does not require any reference images to extract embedded data nor any memorization of the positions of pixels in which data are hidden to extract embedded data. In addition, the proposed reversible data embedding method can control the capacity for hidden data and the quality of images conveying hidden data by controlling the three parameters. Simulation results show the effectiveness of the proposed reversible data embedding method; in particular, it offers images with superior image quality compared with conventional methods. Based on experimental results, the proposed reversible data embedding method has more than 25% embedding capacity improvement ratio. Experimental results show that the proposed reversible data embedding method not only can improve the payload capacity but also can maintain good image quality. In the second proposed method, a reversible data hiding scheme based on histogram modification is proposed. The distribution of pixel differences is used to achieve large hiding capacity while keeping distortion low. The proposed improved histogram-based reversible data hiding approach employed a 3-by-3 box filter prediction scheme and has the capability of embedding two bits for each pixel. The main objective of the proposed improved histogram-based technique is to increase the heights of the peak points around the origin in the histogram, in order to increase the embedding capacity of the proposed improved histogram-based reversible data hiding method. The proposed improved histogram-based reversible data hiding scheme provides high payload capacity for gray level images and maintains high stego-image quality after hiding data. So, the proposed improved histogram-based reversible data hiding method improves the capacity for hidden data and maintains good quality for stego images, simultaneously. Finally, this method restores the original image as well as extracts hidden data from stego image. |