Module: Autocorrelation

Description:

From an greyscale input image, performs an autocorrelation, i.e. a cross-correlation of the image with a translated version of itself (values range between -1 and 1). The centre pixel corresponds to the autocorrelation with 0-translation, giving a correlation value of 1.

Left: example image. Right: resulting autocorrelation

Connections:

Data

[required]
Input image.

Ports:

NOTE : Apart for the compute button, the ports are only avalaible in expert mode. See Commands section.

Preprocess

Centres the Fourier transform, putting the 0-frequency at the image centre.

FFT1

Performs the Fourier transform.

FFT2

Performs the inverse Fourier transform.

Postprocess

Normalises in the Fourier space (for a normalised correlation).

Compute button

Push the button to start the computation, and push the second button to do the same thing, but on the module's output.

Commands:

Additional options can be accessed when typing in the console Autocorrelation COMMAND_NAME. Typing the command again usually reverts back to original settings.

`verbose`

Displays timing information after the computation. Retype to hide info.

`create`

Runs the computation. Returns the name of the output, so it can be used in a script, such as set RESULT [Autocorrelation create].

`expertMode`

Allows to choose whether image centering, FFT, normalisation, etc. is performed. For centred normalised autocorrelation to be computed, expertMode is not required. Retype to revert to simple mode.