fi.helsinki.cs.ohtu.mpeg2.video
Class SimpleDiscreteCosineTransform

java.lang.Object
  fi.helsinki.cs.ohtu.mpeg2.video.SimpleDiscreteCosineTransform

All Implemented Interfaces:

DiscreteCosineTransform, InverseDiscreteCosineTransform

public class SimpleDiscreteCosineTransform
extends java.lang.Object
implements DiscreteCosineTransform, InverseDiscreteCosineTransform

The algorithms in this class are the trivial algorithms directly based on the definitions of the transforms. Both have a complexity of O(n^2), where n is the number of elements in the input. However, the constant factor is quite low due to pre-calculating lookup tables for the more expensive terms in the calculations.

Field Summary

private static java.util.HashMap<java.lang.Integer,double[]>

cosPrecalc

Constructor Summary

SimpleDiscreteCosineTransform()

Method Summary

private static double	C(int a)
private static double[]	getPrecalc(int size) Performs calculating the most expensive term of the DCT process in advance and caches the result.
double[]	transformFromFrequencySpace(int[] input, int size) Transforms one image with the IDCT.
double[]	transformToFrequencySpace(int[] input, int size) Transforms one image with the DCT.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

cosPrecalc

private static java.util.HashMap<java.lang.Integer,double[]> cosPrecalc

Constructor Detail

SimpleDiscreteCosineTransform

public SimpleDiscreteCosineTransform()

Method Detail

transformToFrequencySpace

public double[] transformToFrequencySpace(int[] input,
                                          int size)

Description copied from interface: DiscreteCosineTransform

Transforms one image with the DCT.

Specified by:

transformToFrequencySpace in interface DiscreteCosineTransform

Parameters:

input - The image to be transformed

size - The number of rows and columns in the image

Returns:

The transformed image

transformFromFrequencySpace

public double[] transformFromFrequencySpace(int[] input,
                                            int size)

Description copied from interface: InverseDiscreteCosineTransform

Transforms one image with the IDCT.

Specified by:

transformFromFrequencySpace in interface InverseDiscreteCosineTransform

Parameters:

input - The image to be transformed

size - The number of rows and columns in the image

Returns:

The transformed image

C

private static double C(int a)

Parameters:

a - The coordinate for which to calculate the coefficient

Returns:

1/sqrt(2) if a is zero, 1 otherwise

getPrecalc

private static double[] getPrecalc(int size)

Performs calculating the most expensive term of the DCT process in advance and caches the result. The value at index i * size + j in the returned array will contain the value cos(((2 * j + 1) * i * Math.pi) / (2 * size)). The use of this precalc doesn't in any way hamper the thread-safety of the DCT.

Returns:

The precalculated array.