Name

---

    SCRAMBLE_IMAGE

Purpose

---

    This function returns a version of the provided image in which
    the digital count value locations have been scrambled a specified
    number of times (numberTransformations) using toral automorphism
    (G. Voyatzis and I. Pitas, Applications of toral automorphism in
    image watermarking, Proceedings of the IEEE Conference on Image
    Processing, Volume 2, pp. 237-240, 1996).

Category

---

    Image Processing.

Calling Sequence

---

    Result = SCRAMBLE_IMAGE( image, $
                            key, $
                            numberTransformations,
                            [PERIOD=period], $
                            [/UNSCRAMBLE] )

Inputs

---

    image
      An NxN two-dimensional array containing the image to be
      scrambled.
    key
      A secret key used to define the toral automorphism
      transformation matrix.
    numberTransformations
      The number of toral automorphism transforms to be applied to
      scramble the pixel positions (in the case where the image is
      being unscrambled, this argument should still be defined as the
      original number of transformations used to scramble the image,
      the congugate number with respect to the period of the
      specified toral automorphism due to the provide key will be
      computed).

Keyword Parametrs

---

      PERIOD
        The period of the toral automorphism defined by the
        supplied secret key.
      UNSCRAMBLE
        Set this keyword to unscramble the scambled image by applying
        the conjugate number of transformations K to the number of
        transfomations used to originally scramble the image N where;
        the period of the toral automorphism T defined by the
        supplied secret key follows the constraint that T = N + K.

Return Value

---

    Result is a scrambled version of the provided image that has
    undergone a specied number of transformations or a -1 upon
    failure.
  :ERROR CHECKING:
    RETURN, -1
      If the number of transformations requested by the calling routine
      exceeds the period of the toral automorphism defined by the provide
      secret key (key).
    RETURN, -2
      If the provide image is not square.

Side Effects

---

    None

Requires

---

    None

Modification History

---

    Written by: Carl Salvaggio
    November, 2007 Original code
   

Disclaimer

---

    This source code is provided "as is" and without warranties as to performance
    or merchantability. The author and/or distributors of this source code may
    have made statements about this source code. Any such statements do not
    constitute warranties and shall not be relied on by the user in deciding
    whether to use this source code.
    This source code is provided without any express or implied warranties
    whatsoever. Because of the diversity of conditions and hardware under which
    this source code may be used, no warranty of fitness for a particular purpose
    is offered. The user is advised to test the source code thoroughly before
    relying on it. The user must assume the entire risk of using the source code.