Unlike visual secret sharing schemes which require the halftoning process to encrypt gray-scale or color visual data, image secret sharing solutions operate directly on the bit planes of the digital input. The input image is decomposed into bit-levels which can be viewed as binary images. Using the {k,n} threshold concept, the image secret sharing procedure encrypts individual bit-planes into the binary shares which are used to compose the share images with the representation identical to that of the input image. Depending on the number of the bits used to represent the secret (input) image, the shares can contain binary, gray-scale or color random information. Thus, the degree of protection afforded by image secret sharing methods increases with the number of bits used to represent the secret image.

		®		+		=
	Secret gray-scale image		Share 1		Share 2		Decrypted image

The decryption operations are performed on decomposed bit-planes of the share images. Using the contrast properties of the conventional {k,n}-schemes, the decryption procedure uses shares' bits to recover the original bit representation and compose the secret image. The decrypted output is readily available in a digital format, and is identical to the input image. Because of the symmetry constraint imposed on the encryption and decryption process, image secret sharing solutions hold the perfect reconstruction property. This feature in conjunction with the overall simplicity of the approach make this approach attractive for real-time secret sharing based encryption/decryption of natural images.   ® + =     Secret color image   Share 1   Share 2   Decrypted image