  Visual secrete sharing (VSS) is an encryption technique that utilizes human
visual system in the recovering of the secret image and it does not require any
complex calculation. Pixel expansion has been a major issue of VSS schemes. A
number of probabilistic VSS schemes with minimum pixel expansion have been
proposed for binary secret images. This paper presents a general probabilistic
(k, n)-VSS scheme for gray-scale images and another scheme for color images.
With our schemes, the pixel expansion can be set to a user-defined value. When
this value is 1, there is no pixel expansion at all. The quality of
reconstructed secret images, measured by Average Relative Difference, is
equivalent to Relative Difference of existing deterministic schemes. Previous
probabilistic VSS schemes for black-and-white images with respect to pixel
expansion can be viewed as special cases of the schemes proposed here
