本週課程主題是討論
J. Fridrich 論文
A New Steganographic Method for Palette Images 的核心觀念！我們從本篇論文的摘要(abstract)開始討論, 希望讓同學體認到一篇論文的菁華, 其實都在這邊了！
AbstractIn this paper, we present a new steganographic technique for embedding messages in palette-based images, such as GIF files. The new technique embeds one message bit into one pixel (its pointer to the palette). The pixels for message embedding are chosen randomly using a
pseudo-random number generator seeded with a
secret key. For each pixel at which one message bit is to be embedded, the palette is searched for closest colors. The closest color with the same parity as the message bit is then used instead of the original color. This has the advantage that both the overall change due to message embedding and the maximal change in colors of pixels is smaller than in methods that perturb the least significant bit of indices to a luminance-sorted palette, such as
EZ Stego. Indeed, numerical experiments indicate that the new technique introduces approximately four times less distortion to the carrier image than EZ Stego. The maximal color change is 45 times smaller for the new technique than that of EZ Stego. A technique that introduces less distortion to the carrier image will generally cause changes that are more difficult to detect, and will therefore provide more security.
在了解核心觀念之後, 請同學重新思考上週在
Homework Show @ IHC 所提出的問題, 看看是否已經可以解答自己的問題了。本週的作業是重新在閱讀一次本篇論文, 然後請同學針對自己與同學們提出的問題去回應。
