ok let me try this one.

suppose u want to choose the key based on the day and last 2 digits of some of
your favorite people. assuming that the matrix supports this key system in terms
of dimensions.

try this for a 256 X 256 image

image_X = rand(256); % generating any random image of size 256 X 256

key = [randint(256,1,[1,31]), randint(256,1,[1,99])];

watermark_indices = image_X(key);

hope this helps

david hali wrote:

Thanks. The 2nd one ,let me expalin it in this way for example , Image X

,and compute 2nd level discrete Haar wavelet tranform of host image X , and

embed watermark in LL band, but want to select the coeff. using secret key

or seed and use the same secret key or seed to extract the watermark , any

one who doesnt know secret key , cant exract the watermark. Hope u

understand me now .

Thanks in advance once more

>From: Amit Pathania

>To: david hali , m...

>Subject: Re: Hello friend Amit

>Date: Sun, 17 Jun 2007 17:21:33 -0700 (PDT)

>

>the way i understand your question, u want to pick say 5 largest numbers

>from a 5 by 5 matrix where all elements of the matrix are unique .. look at

>the code below-

>

> X = rand(5,5);

> X_sort = sort(X(:),'descend');

>

> largest_5 = X_sort(1:5);

>

> i could not understand the second question properly, please elaborate

>what you mean by a Key. if u want to select elements based on a pattern

>just generate the indices and select them from your given matrix.

>david hali wrote:

> Hello Dear Amit

>Hope You wont mind by emailing privately

>I have seen your suggestion how to select randomly N elements from X

>matrix. But my question is how to select N largest elements from matrix X?.

>let X be 256 by 256 and the second question is how to select cofficients

>from matrix Y by using Key? for example want to select position

>Y(1,3),Y(2,7) and so on, let Y be 256 by 256 size

>thanks in advance

>hali

>