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# vision.IDCT System object

Package: vision

Compute 2-D inverse discrete cosine transform

## Description

The IDCT object computes 2-D inverse discrete cosine transform of the input signal. The number of rows and columns of the input matrix must be a power of 2.

## Construction

H = vision.IDCT returns a System object, H, used to compute the two-dimensional inverse discrete cosine transform (2-D IDCT) of a real input signal.

H = vision.IDCT(Name,Value) returns a 2-D inverse discrete cosine transform System object, H, with each specified property set to the specified value. You can specify additional name-value pair arguments in any order as (Name1, Value1,...,NameN,ValueN).

## Properties

 SineComputation Specify how the System object computes sines and cosines as Trigonometric function, or Table lookup. This property must be set to Table lookup for fixed-point inputs.

## Methods

 clone Create 2-D inverse discrete cosine transform object with same property values getNumInputs Number of expected inputs to step method getNumOutputs Number of outputs from step method isLocked Locked status for input attributes and nontunable properties release Allow property value and input characteristics changes step Compute 2-D inverse discrete cosine transform of the input

## Examples

Use 2-D discrete cosine transform (DCT) to analyze the energy content in an image. Set the DCT coefficients lower than a threshold of 0. Reconstruct the image using 2-D inverse discrete cosine transform (IDCT).

``` hdct2d = vision.DCT;
J = step(hdct2d, I);
imshow(log(abs(J)),[]), colormap(jet(64)), colorbar

hidct2d = vision.IDCT;
J(abs(J) < 10) = 0;
It = step(hidct2d, J);
figure, imshow(I, [0 255]), title('Original image')
figure, imshow(It,[0 255]), title('Reconstructed image')

```

## Algorithms

This object implements the algorithm, inputs, and outputs described on the 2-D IDCT block reference page. The object properties correspond to the block parameters.