edu.emory.mathcs.jtransforms.fft

Class RealFFTUtils_2D

java.lang.Object

edu.emory.mathcs.jtransforms.fft.RealFFTUtils_2D

public class RealFFTUtils_2D
extends Object

This is a set of utility methods for R/W access to data resulting from a call to the Fourier transform of real data. Memory optimized methods, namely

• DoubleFFT_2D.realForward(double[])
• DoubleFFT_2D.realForward(double[][])
• FloatFFT_2D.realForward(float[])
• FloatFFT_2D.realForward(float[][])

are implemented to handle this case specifically. However, packing of the data in the data array is somewhat obscure. This class provides methods for direct access to the data, without the burden of all necessary tests.

Example for Fourier Transform of real, double precision 1d data

   DoubleFFT_2D fft = new DoubleFFT_2D(rows, columns);
   double[] data = new double[2 * rows * columns];
   ...
   fft.realForwardFull(data);
   data[r1 * 2 * columns + c1] = val1;
   val2 = data[r2 * 2 * columns + c2];
 

is equivalent to

   DoubleFFT_2D fft = new DoubleFFT_2D(rows, columns);
   RealFFTUtils_2D unpacker = new RealFFTUtils_2D(rows, columns);
   double[] data = new double[rows * columns];
   ...
   fft.realForward(data);
   unpacker.pack(val1, r1, c1, data);
   val2 = unpacker.unpack(r2, c2, data, 0);
 

Even (resp. odd) values of c correspond to the real (resp. imaginary) part of the Fourier mode.

Example for Fourier Transform of real, double precision 2d data

   DoubleFFT_2D fft = new DoubleFFT_2D(rows, columns);
   double[][] data = new double[rows][2 * columns];
   ...
   fft.realForwardFull(data);
   data[r1][c1] = val1;
   val2 = data[r2][c2];
 

is equivalent to

   DoubleFFT_2D fft = new DoubleFFT_2D(rows, columns);
   RealFFTUtils_2D unpacker = new RealFFTUtils_2D(rows, columns);
   double[][] data = new double[rows][columns];
   ...
   fft.realForward(data);
   unpacker.pack(val1, r1, c1, data);
   val2 = unpacker.unpack(r2, c2, data, 0);
 

Even (resp. odd) values of c correspond to the real (resp. imaginary) part of the Fourier mode.

Author:

Sébastien Brisard

Constructor Summary

Constructors

Constructor and Description
RealFFTUtils_2D(int rows, int columns) Creates a new instance of this class.

Method Summary

Modifier and Type	Method and Description
int	getIndex(int r, int c) Returns the 1d index of the specified 2d Fourier mode.
void	pack(double val, int r, int c, double[][] packed) Sets the specified Fourier mode of the transformed data.
void	pack(double val, int r, int c, double[] packed, int pos) Sets the specified Fourier mode of the transformed data.
void	pack(float val, int r, int c, float[][] packed) Sets the specified Fourier mode of the transformed data.
void	pack(float val, int r, int c, float[] packed, int pos) Sets the specified Fourier mode of the transformed data.
double	unpack(int r, int c, double[][] packed) Returns the specified Fourier mode of the transformed data.
double	unpack(int r, int c, double[] packed, int pos) Returns the specified Fourier mode of the transformed data.
float	unpack(int r, int c, float[][] packed) Returns the specified Fourier mode of the transformed data.
float	unpack(int r, int c, float[] packed, int pos) Returns the specified Fourier mode of the transformed data.

Methods inherited from class java.lang.Object

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

Constructor Detail

RealFFTUtils_2D

public RealFFTUtils_2D(int rows,
                       int columns)

Creates a new instance of this class. The size of the underlying DoubleFFT_2D or FloatFFT_2D must be specified.

Parameters:

rows - number of rows

columns - number of columns

Method Detail

getIndex

public int getIndex(int r,
                    int c)

Returns the 1d index of the specified 2d Fourier mode. In other words, if packed contains the transformed data following a call to DoubleFFT_2D.realForward(double[]) or FloatFFT_2D.realForward(float[]), then the returned value index gives access to the [r][c] Fourier mode

• if index == Integer.MIN_VALUE, then the Fourier mode is zero,
• if index >= 0, then the Fourier mode is packed[index],
• if index < 0, then the Fourier mode is -packed[-index],

Parameters:

r - the row index

c - the column index

Returns:

the value of index

pack

public void pack(double val,
                 int r,
                 int c,
                 double[] packed,
                 int pos)

Sets the specified Fourier mode of the transformed data. The data array results from a call to DoubleFFT_2D.realForward(double[]).

Parameters:

val - the new value of the [r][c] Fourier mode

r - the row index

c - the column index

packed - the transformed data

pos - index of the first element in array packed

pack

public void pack(double val,
                 int r,
                 int c,
                 double[][] packed)

Sets the specified Fourier mode of the transformed data. The data array results from a call to DoubleFFT_2D.realForward(double[][]).

Parameters:

val - the new value of the [r][c] Fourier mode

r - the row index

c - the column index

packed - the transformed data

pack

public void pack(float val,
                 int r,
                 int c,
                 float[] packed,
                 int pos)

Sets the specified Fourier mode of the transformed data. The data array results from a call to FloatFFT_2D.realForward(float[]).

Parameters:

val - the new value of the [r][c] Fourier mode

r - the row index

c - the column index

packed - the transformed data

pos - index of the first element in array packed

pack

public void pack(float val,
                 int r,
                 int c,
                 float[][] packed)

Sets the specified Fourier mode of the transformed data. The data array results from a call to FloatFFT_2D.realForward(float[][]).

Parameters:

val - the new value of the [r][c] Fourier mode

r - the row index

c - the column index

packed - the transformed data

unpack

public double unpack(int r,
                     int c,
                     double[] packed,
                     int pos)

Returns the specified Fourier mode of the transformed data. The data array results from a call to DoubleFFT_2D.realForward(double[]).

Parameters:

r - the row index

c - the column index

packed - the transformed data

pos - index of the first element in array packed

Returns:

the value of the [r][c] Fourier mode

unpack

public double unpack(int r,
                     int c,
                     double[][] packed)

Returns the specified Fourier mode of the transformed data. The data array results from a call to DoubleFFT_2D.realForward(double[][]) .

Parameters:

r - the row index

c - the column index

packed - the transformed data

Returns:

the value of the [r][c] Fourier mode

unpack

public float unpack(int r,
                    int c,
                    float[] packed,
                    int pos)

Returns the specified Fourier mode of the transformed data. The data array results from a call to FloatFFT_2D.realForward(float[]) .

Parameters:

r - the row index

c - the column index

packed - the transformed data

pos - index of the first element in array packed

Returns:

the value of the [r][c] Fourier mode

unpack

public float unpack(int r,
                    int c,
                    float[][] packed)

Returns the specified Fourier mode of the transformed data. The data array results from a call to FloatFFT_2D.realForward(float[][]) .

Parameters:

r - the row index

c - the column index

packed - the transformed data

Returns:

the value of the [r][c] Fourier mode