2D Data Objects

Data objects come in two varieties: volume data and projection data (sinograms), and can be manipulated using the following commands:

create

id = astra.data2d.create('-vol', vol_geom)
id = astra.data2d.create('-vol', vol_geom, initializer)

This creates an initialized 2D volume data object for the geometry vol_geom.

Initializer may be:

  • a scalar: the object is initialized with this constant value.

  • a matrix: the object is initialized with the contents of this matrix. The matrix must be of size (y,x) as defined in the volume geometry. It must be of class single, double or logical.

If an initializer is not present, the volume is initialized to zero.

id = astra.data2d.create('-sino', proj_geom)
id = astra.data2d.create('-sino', proj_geom, initializer)

This creates an initialized 2D projection data object for the geometry proj_geom.

Initializer may be:

  • a scalar: the object is initialized with this constant value.

  • a matrix: the object is initialized with the contents of this matrix. The matrix must be of size (angles,u), where u is the number of detector pixels as defined in the projection geometry. It must be of class single, double or logical.

If an initializer is not present, the volume is initialized to zero.

get

A = astra.data2d.get(id)

This fetches the data object as a 2D array with dtype float32.

get_shared

A = astra.data2d.get_shared(id)

This fetches the data object as a 2D numpy array sharing its memory with the Astra object. Changes to the returned array will be visible to Astra, and vice versa. Deleting the Astra object while the resulting Python object still exists will lead to undefined behaviour and potentially memory corruption and crashes.

get_single

Only available in MATLAB interface.

set / store

astra.data2d.store(id, A)

This stores the matrix A in the data object. The dimensions of A must be the same as the existing data object.

Set and store are synonyms in the MATLAB interface.

get_geometry

geom = astra.data2d.get_geometry(id)

This gets the (volume or projection) geometry attached to the object.

NB: This is not fully implemented yet and the return value may not accurately represent the geometry.

change_geometry

astra.data2d.change_geometry(id, geom)

This changes the (volume or projection) geometry attached to the object. It cannot change the dimensions of the data object. This can be used to change the pixel dimensions or projection angles, for example.

delete

astra.data2d.delete(id)

Free the memory of a data object.

clear

astra.data2d.clear()

Free all data objects.

info

astra.data2d.info()

Print basic information about all allocated data objects.

shepp_logan

Added in version 2.2.

id, data = astra.data2d.shepp_logan(vol_geom, modified)

Creates a Shepp-Logan transform. modified=True creates a phantom with improved contrast (default).