# Fourrier Transform

A Fourier transform (FT) is a mathematical transform that decomposes functions into frequency components, which are represented by the output of the transform as a function of frequency. This transformation is widely used in imaging because it allows to see signals at regular frequencies.

Siril allows to transform an image in the frequency space thanks to a
Fast Fourier Transform
algorithm. The result is in the form of two images. The first one,
automatically loaded, contains the magnitude (or modulus) of the transform, the
second one contains the phase. The location of the two images must be entered
in the **Direct Transform** tab (see illustration below) of the dialog. It is
then possible to modify the modulus image by removing frequency peaks
corresponding to unwanted signals. It is important not to forget to save the
changes.

The Centered option, when checked, centers the origin of the Direct Fourier Transform. If not, the origin is at the top-left corner.

To reconstruct the image, click on the **Inverse Transform** tab and enter the
filepath of the modulus and phase images.

Siril command line

```
fftd modulus phase
```

**modulus**and

**phase**given in argument are the names of the saved in FITS files

Siril command line

```
ffti modulus phase
```

**modulus**and

**phase**arguments are the input file names, the result will be the new loaded image