Error: Missing variable or function.
%COXWMK Insert a random watermark.% = COXWMK(I) watermarks the grayscale picture I using
% Cox's scheme with default parameters. J is the watermarked
% picture and W is the watermark.
% The watermark W is drawn from a Normal random process N(0,1)
% if it is not given by the user as last parameter.
%
% = COXWMK(I, Alpha, N) watermarks the grayscale picture I
% using modifying the Nth largest DCT coefficients v_i in the
% following way: v_i := v_i * (1 + Alpha * w_i) where w_i
% are the components of the watermak.
%
% Use IMSHOW(mat2gray(J)) to display the output.
%
% See: COXDETECT
% Fabien A.P. Petitcolas 26-11-97
% Copyright (c) 1997 by the University of Cambridge
% $Revision: 0.6$
% References:
% 1) Ross J. Anderson,7 editor. Information hiding: first
% international workshop, volume 1174 of Lecture notes
% in computer science. University of Cambridge, Isaac
% Newton Institute, Springer Verlag, Berlin, Germany,
% May 1996.
% 2) Ingemar J. Cox, Joe Kilian, Tom Leighton, and Talal
% Shamoon. A secure, robust watermark for multimedia.
% In Anderson , pages 183-206
function = CoxWmk(I, alpha, N,w)
if (nargin == 1)
N = 1000;
alpha = 0.1;
W = randn(1,N);
elseif (nargin == 2)
N = 1000;
W = randn(1,N);
elseif (nargin == 3)
W = randn(1,N);
end
sI = size(I);
if ((sI(1) * sI(2)) < N)
error('Image too small or too many coefficients.');
end
% Generate the random watermark
%W = randn(1,N);
% Compute the DCT of the image
DCTI = dct2(I);
% Find the N largest coefficients in the DCT matrix
% Better if the extraction of the N largest was done
% at the same time than the computation of the DCT...
Index = FindNLargest(abs(DCTI), N);
% Modify these coefficients
for i = 1:N
DCTI(Index(1,i),Index(2,i)) = DCTI(Index(1,i),Index(2,i)) * (1 + alpha * W(i));
end
% Simply take the inverse DCT of the modifyied matrix
J = idct2(DCTI);
subplot(1,2,1);imshow(I);title("原始图像");
subplot(1,2,2);imshow(J);title("加入水印图像");
imwrite(J,"graywatermark.jpg");
运行此函数提示Error: Missing variable or function.不知怎么回事，求教。 个人水平专业有限, 建议楼主说清楚些!
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