A secret sharing scheme suitable for encrypting colour images is introduced. The required colour shares are obtained during encryption by operating at the bit-levels. Perfect reconstruction is achieved by the decryption module using only logical operations. Introduction: Cryptographic secret sharing techniques are essential for cost-effective image protection of scanned documents and digital personal photographs that are distributed via public networks. These techniques are based on the principle of sharing secret information among a group of participants. The shared secret can be recovered only when a coalition of willing participants are polling their encrypted images, the so-called shares, together [1] . Using the well-known {k, n}-visual sharing scheme (VSS) [1] the commonly used solutions first produce a halftoned version of the input colour image and then apply the VSS strategy to generate n shares. If k (or more) shares are stacked together, the decryption process allows for the recovery of the visual information. In the case of the simple {2, 2}-VSS, the dithered version of the continuous-tone colour image is encrypted into two shares [1] . Both shares should be stacked together for the visual message to be revealed. Note that colour visual cryptography schemes currently in use generate decrypted images with noticeable visual impairments. This can be attributed to (i) the need for binary or dithered inputs [2] , and (ii) the limited number of colours for which the schemes work well [3] . It is therefore necessary to develop a new method capable of processing true colour images in a cost-effective manner.
R. Lukac and K.N. Plataniotis REF proposed a secret sharing technique for cryptographic color image processing.
Colour image secret sharing
Electronics Letters
Mathematics