Accelerating the pace of engineering and science

# Documentation Center

• Trial Software

# vision.DCT System object

Package: vision

Compute 2-D discrete cosine transform

## Description

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

## Construction

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

H = vision.DCT(Name,Value) returns a 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 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 discrete cosine transform on input

## Examples

Use 2-D discrete cosine transform to analyze the energy content in an image. Set the DCT coefficients lower than a threshold of 0, and then reconstruct the image using the 2-D inverse discrete cosine transform object.

``` 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 DCT block reference page. The object properties correspond to the block parameters.