| Summary: | 碩士 === 國立交通大學 === 資訊科學與工程研究所 === 98 ===
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created from a grayscale image of a secret document, yielding a steganographic effect
of hiding the secret document into the mosaic image, though visibly. The selection of
the most similar target image from a database is based on a newly-proposed k-feature
of the grayscale value, which speeds up the image creation process. Finally, for secret
sharing, a secret image is shared to yield multiple secret-fragment-visible mosaic
images. In order to disperse tile images evenly in selected target images, the target
images take turns randomly to pick appropriate tile images.
In addition, various security enhancement measures were proposed to make the
embedded data more random to prevent hackers’ attacks. Experimental results show
the feasibility of the proposed methods for image creation and data hiding
applications. In this study, a new type of art image is created, which is called
secret-fragment-visible mosaic image. And this kind of new mosaic image is used for
three applications of data hiding, namely, covert communication, steganography, and
secret sharing.
First, the newly-proposed secret-fragment-visible mosaic image is created to be
composed of rectangular-shaped fragments which come from division of a secret
image. A new 1-D h-colorscale is proposed to represent the color distribution of an
image based on the color feeling of human vision. To create a secret-fragment-visible
mosaic image, a new image similarity measure based on the h-colorscale is proposed,
and the most similar candidate image from an image database is selected accordingly
as a target image. Then, a greedy algorithm is adopted to fit every tile image in the
secret image into an appropriate block in the target image. Furthermore, to solve the
problem of using an insufficiently-large database, a remedy method by enlarging the
size of a target image is also proposed. Secondly, for covert communication, based on
the fact that tile images which are in an identical histogram bin have similar colors,
the tile images in an identical histogram bin are reordered, or equivalently, the relative
positions of the tile images are switched, to embed secret message bits imperceptibly.
Third, for image steganography, a grayscale secret-fragment-visible mosaic image is
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