Essential secret image sharing with increasable shadows

Li et al. and Yang et al. proposed ( t,s,k,n )-essential secret image sharing methods to share a secret image into essential shadows and nonessential shadows. However, if the shadows have been distributed to the holders and extra shadows are required, the processes of regenerating and retransmitting shadows are necessary. In the proposed method, when receiving t essential shadows and k − t nonessential shadows, the total size of the adopted shadow is the same as the size of the secret image. Most importantly, the proposed method achieves less size of total required shadows (when using the minimal essential shadows) than what was proposed by Li et al. and achieves less size of essential shadow than the method contended by Yang et al. Moreover, we can have the additional shadows relate to other existing shadows without regenerating.