Random grid-based threshold visual secret sharing with improved visual quality and lossless recovery ability

Visual secret sharing (VSS) by random grids (RG) has gained much attention since it avoids the pixel expansion problem as well as requires no basic matrixes design. However, most of the previous RG-based threshold VSS still suffer from low visual quality or worse reconstructed secrets when more shadows are stacked. In this paper, a new RG-based threshold VSS with improved visual quality and lossless recovery ability is proposed. The random bits are utilized to improve the visual quality as well as to decrease the darkness of the reconstructed secret image. And the secret image can be losslessly recovered in the proposed scheme if the computational device is available. Simulation results and analyzes show the effectiveness of the proposed scheme. In addition, this paper gave the preliminary definition and evaluation of progressive secret sharing (PSS) based on mathematical differential and expectations.