How an image is divided into number of shares in visual cryptography?

Answer 1

as a simple example assume you want divide a gray level secret image to two shares.

Each pixel in the secret image is expanded to four subpixels in each share that consist of white and black so width and height of shares is twice of secret image.

first share is an image wich has random pixels of black or white with equal probability.

in second share, if corresponding pixel in main secret image is white then the pixel in second share is the same as first share and if pixel in the secret image is black, corresponding pixel in second share would be inverse of the same pixel in first share.