# Documentation

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# vision.IDCT System object

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.

### 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.

## 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

 step Compute 2-D inverse discrete cosine transform of the input
Common to All System Objects
`clone`

Create System object with same property values

`getNumInputs`

Expected number of inputs to a System object

`getNumOutputs`

Expected number of outputs of a System object

`isLocked`

Check locked states of a System object (logical)

`release`

Allow System object property value changes

## 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; I = double(imread('cameraman.tif')); 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.