Affiliations: Department of Information Engineering and Computer
Science, Feng Chia University, Taichung, Taiwan, 40724. E-mail: ccc@cs.ccu.edu.tw | Department of Computer Science and Information
Engineering, National Chung Cheng University Chiayi, Taiwan, 621. E-mail: {gary,tcs92}@cs.ccu.edu.tw
Abstract: This study proposes a new secret image sharing method based on the
(t,n)-threshold. The sharing method is completed through three main steps: (1)
quantizing the secret image, (2) generating n shadows from the quantized image,
and (3) sharing the n shadows among n cover images. Our goal is both to attain
good stego-image and secret image quality preservation effects and to limit the
size of each shadow image down to 1/t of that of the secret image for
convenient transmission and storage. In the first step, the secret image is
divided into non-overlapping 4 × 4 blocks that are quantized
according to the results of block testing. Each block, after the block testing
procedure, is judged to be either a smooth block or a non-smooth one. Smooth
blocks can be neatly restored after being hidden into the cover image, while
non-smooth blocks can be somewhat lossy, but such modification is perceptually
invisible. The second step is to apply Shamir's (t,n)-threshold,
which uses a (t−1)-degree polynomial to generate n shadows so that the secret
image can be restored from any t out of n shadows. The last step involves a
modulo operation to hide the n shadows in n cover images. According to our
experimental results, the PSNR values of the reconstructed secret images by our
method center around 39 dB, outperforming other recent methods.
