2-D discrete cosine transform   B = dct2(A) B = dct2(A,m,n) B =
dct2(A,[m n])   B = dct2(A) returns the two-dimensional discrete
cosine transform of A. The matrix B is the same size as A and
contains the discrete cosine transform coefficients B(k1,k2).  B
= dct2(A,m,n) pads the matrix A with 0's to size m-by-n before
transforming. If m or n is smaller than the corresponding
dimension of A, dct2 truncates A.  B = dct2(A,[m n]) same as
above.  Class Support  A can be numeric or logical. The returned
matrix B is of class double.   The commands below compute the
discrete cosine transform for the autumn image. Notice that most
of the energy is in the upper left corner.  RGB =
imread('autumn.tif'); I = rgb2gray(RGB); J = dct2(I);
imshow(log(abs(J)),[]), colormap(jet(64)), colorbar  Now set
values less than magnitude 10 in the DCT matrix to zero, and
then reconstruct the image using the inverse DCT function idct2.
J(abs(J) < 10) = 0; K = idct2(J); figure, imshow(K,[0 255])
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