Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / signal-1.1.3 / dctmtx.m

diff --git a/octave_packages/signal-1.1.3/dctmtx.m b/octave_packages/signal-1.1.3/dctmtx.m
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+## Copyright (C) 2001 Paul Kienzle <pkienzle@users.sf.net>
+##
+## This program is free software; you can redistribute it and/or modify it under
+## the terms of the GNU General Public License as published by the Free Software
+## Foundation; either version 3 of the License, or (at your option) any later
+## version.
+##
+## This program is distributed in the hope that it will be useful, but WITHOUT
+## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+## details.
+##
+## You should have received a copy of the GNU General Public License along with
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## T = dctmtx (n)
+## Return the DCT transformation matrix of size n x n.
+##
+## If A is an n x n matrix, then the following are true:
+##     T*A    == dct(A),  T'*A   == idct(A)
+##     T*A*T' == dct2(A), T'*A*T == idct2(A)
+##
+## A dct transformation matrix is useful for doing things like jpeg
+## image compression, in which an 8x8 dct matrix is applied to
+## non-overlapping blocks throughout an image and only a subblock on the
+## top left of each block is kept.  During restoration, the remainder of
+## the block is filled with zeros and the inverse transform is applied
+## to the block.
+##
+## See also: dct, idct, dct2, idct2
+
+function T = dctmtx(n)
+  if nargin != 1
+    print_usage;
+  endif
+
+  if n > 1
+    T = [ sqrt(1/n)*ones(1,n) ; \
+        sqrt(2/n)*cos((pi/2/n)*([1:n-1]'*[1:2:2*n])) ];
+  elseif n == 1
+    T = 1;
+  else
+    error ("dctmtx: n must be at least 1");
+  endif
+
+endfunction