An Intragroup and Intergroup Multiple Secret Images’ Sharing Scheme with Each Participant Holding One Shadow Image

Algorithm 1

The shadow image generation process of SIS within one group and between groups.

	Input: the secret images and the order numbers of the participants
	Output: the shadow images
	Step 1: repeat Steps 2–7 for each pixel of the secret images , and , where
	Step 2: write the polynomial expressions for SIS within and between groups
	Step 3: find the equations that the sharing coefficients need to satisfy
	Step 4: count the variables and the number of equations that need to be satisfied
	Step 5: pick coefficients randomly and assign them to a random number between 0 and 250
	Step 6: use the inverse matrix method to solve the system and find the values of the remaining unspecified coefficients
	Step 7: calculate the values of the shadow pixel based on the sharing polynomial, in which the polynomial coefficients are known