This demo lets the user type in a text message, choose an image to hide the message in (from the list of demo images shipped with MATLAB), and choose the bit plane to encode the message in. It converts the message string into ASCII code and then into a binary string. It assigns the bits to the selected bit plane of the image pixels starting at the upper left pixel and going down the column(s). Because the text is encoded in ASCII and mixed with the gray levels bits, it's not noticeable.