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## Functions

int | vips_fwfft () |

int | vips_invfft () |

int | vips_freqmult () |

int | vips_spectrum () |

int | vips_phasecor () |

## Description

To and from Fourier space, filter in Fourier space, convert Fourier-space images to a displayable form.

## Functions

### vips_fwfft ()

int vips_fwfft (,`VipsImage *in`

,`VipsImage **out`

);`...`

Transform an image to Fourier space.

VIPS uses the fftw Fourier Transform library. If this library was not available when VIPS was configured, these functions will fail.

See also: `vips_invfft()`

.

[method]

### vips_invfft ()

int vips_invfft (,`VipsImage *in`

,`VipsImage **out`

);`...`

Optional arguments:

: only output the real part`real`

Transform an image from Fourier space to real space. The result is complex.
If you are OK with a real result, set * real*
, it's quicker.

VIPS uses the fftw Fourier Transform library. If this library was not available when VIPS was configured, these functions will fail.

See also: `vips_fwfft()`

.

[method]

### vips_freqmult ()

int vips_freqmult (,`VipsImage *in`

,`VipsImage *mask`

,`VipsImage **out`

);`...`

Multiply * in*
by

*in Fourier space.*

`mask`

* in*
is transformed to Fourier space, multipled with

*, then transformed back to real space. If*

`mask`

*is already a complex image, just multiply then inverse transform.*

`in`

See also: `vips_invfft()`

, `vips_mask_ideal()`

.

[method]

### vips_spectrum ()

int vips_spectrum (,`VipsImage *in`

,`VipsImage **out`

);`...`

Make a displayable (ie. 8-bit unsigned int) power spectrum.

If * in*
is non-complex, it is transformed to Fourier space. Then the
absolute value is passed through

`vips_scale()`

in log mode, and `vips_wrap()`

.See also: `vips_fwfft()`

, `vips_scale()`

, `vips_wrap()`

.

[method]

### vips_phasecor ()

int vips_phasecor (,`VipsImage *in1`

,`VipsImage *in2`

,`VipsImage **out`

);`...`

Convert the two input images to Fourier space, calculate phase-correlation, back to real space.

See also: `vips_fwfft()`

, `vips_cross_phase()`

,