Discrete cosine transform (DCT)
DCT object computes the discrete cosine
transform (DCT) of input.
To compute the DCT of input:
Starting in R2016b, instead of using the
to perform the operation defined by the System
object™, you can
call the object with arguments, as if it were a function. For example,
= step(obj,x) and
y = obj(x) perform
dct = dsp.DCT returns
a discrete cosine transform (DCT) object,
to compute the DCT of a real or complex input signal.
dct = dsp.DCT(' returns a DCT object,
dct, with each
property set to the specified value.
Method to compute sines and cosines
Specify how the DCT object computes the trigonometric values
|step||Discrete cosine transform (DCT) of input|
Note: This example runs only in R2016b or later. If you are using an earlier release, replace each call to the function with the equivalent
step syntax. For example, myObject(x) becomes step(myObject,x).
Use DCT to analyze the energy content in a sequence:
x = (1:128).' + 50*cos((1:128).'*2*pi/40); dct = dsp.DCT; X = dct(x);
Set the DCT coefficients which represent less than 0.1% of the total energy to 0 and reconstruct the sequence using IDCT.
[XX, ind] = sort(abs(X),1,'descend'); ii = 1; while (norm([XX(1:ii);zeros(128-ii,1)]) <= 0.999*norm(XX)) ii = ii+1; end disp(['Number of DCT coefficients that represent 99.9%',... 'of the total energy in the sequence: ',num2str(ii)]);
Number of DCT coefficients that represent 99.9%of the total energy in the sequence: 10
XXt = zeros(128,1); XXt(ind(1:ii)) = X(ind(1:ii)); idct = dsp.IDCT; xt = idct(XXt); plot(1:128,[x xt]); legend('Original signal','Reconstructed signal',... 'location','best');
This object implements the algorithm, inputs, and outputs described on the DCT block reference page. The object properties correspond to the block parameters.
Usage notes and limitations:
See System Objects in MATLAB Code Generation (MATLAB Coder).