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dsp.IDCT System object

Package: dsp

Inverse discrete cosine transform (IDCT)


The IDCT object computes the inverse discrete cosine transform (IDCT) of an input.

To compute the IDCT of an input:

  1. Define and set up your IDCT object. See Construction.

  2. Call step to compute the IDCT of an input according to the properties of dsp.IDCT. The behavior of step is specific to each object in the toolbox.

    Note:   Starting in R2016b, instead of using the step method to perform the operation defined by the System object™, you can call the object with arguments, as if it were a function. For example, y = step(obj,x) and y = obj(x) perform equivalent operations.


H = dsp.IDCT returns a inverse discrete cosine transform (IDCT) object, H. This object computes the IDCT of a real or complex input signal using the Table lookup method.

H = dsp.IDCT('PropertyName',PropertyValue,...) returns an inverse discrete cosine transform (IDCT) object, H, with each property set to the specified value.



Method to compute sines and cosines

Specify how the IDCT object computes the trigonometric function values as Trigonometric function or Table lookup. You must set this property to Table lookup for fixed-point inputs. The default is Table lookup.

 Fixed-Point Properties


cloneCreate inverse discrete cosine transform object with same property values
getNumInputsNumber of expected inputs to step method
getNumOutputsNumber of outputs of step method
isLockedLocked status for input attributes and nontunable properties
releaseAllow property value and input characteristics changes
stepInverse discrete cosine transform (IDCT) of input


Use DCT to analyze the energy content in a sequence:

x = (1:128).' + 50*cos((1:128).'*2*pi/40);
hdct = dsp.DCT;

X = step(hdct, 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;

disp(['Number of DCT coefficients that represent 99.9%',...
'of the total energy in the sequence: ',num2str(ii)]); 
XXt = zeros(128,1);
XXt(ind(1:ii)) = X(ind(1:ii));
hidct = dsp.IDCT;
xt = step(hidct, XXt);

plot(1:128,[x xt]);
legend('Original signal','Reconstructed signal',...


This object implements the algorithm, inputs, and outputs described on the IDCT block reference page. The object properties correspond to the block parameters.

Introduced in R2012a

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