2D Data Objects

Volume and projection data

ASTRA data objects come in two varieties: volume data and projection data (sinograms). A data object can be created using the following commands:

create

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

id = astra_mex_data2d('create', '-vol', vol_geom);
id = astra_mex_data2d('create', '-vol', vol_geom, initializer);

Create 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 by the volume geometry. In Python, it must be convertible to float32. In MATLAB, it must be of class single, double or logical.

If no initializer is given, the volume is initialized to all zeros.

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

id = astra_mex_data2d('create', '-sino', proj_geom);
id = astra_mex_data2d('create', '-sino', proj_geom, initializer);

Create 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 defined by the projection geometry. In Python, it must be convertible to float32. In MATLAB, it must be of class single, double or logical.

If no initializer is given, the projection data object is initialized to all zeros.

link

id = astra.data2d.link('-sino', proj_geom, array)
id = astra.data2d.link('-vol', vol_geom, array)

Create an ASTRA data object that shares its memory with the specified CPU or GPU array supporting the DLPack interface. This includes arrays from NumPy, PyTorch, JAX, TensorFlow and CuPy libraries. The array must be contiguous, have float32 dtype, and a shape compatible with the specified geometry. No copying is performed, so changes to the linked array will be visible to ASTRA, and vice versa. Linking the array increments the reference count of the underlying memory, so deleting the original array will not destroy the created ASTRA object.

Added in version 2.5: Accept any 2D array supporting DLPack protocol. Before, only NumPy arrays were supported.

Phantom generation

ASTRA includes a built-in generator for the Shepp-Logan phantom:

shepp_logan

Added in version 2.2.

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

Create a Shepp-Logan phantom as an ASTRA volume data object (id), and a NumPy array (data). modified=True creates a phantom with improved contrast (default).

API

get

A = astra.data2d.get(id)

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

A = astra_mex_data2d('get', id);

Fetch the data object as a 2D matrix of class double.

get_shared

A = astra.data2d.get_shared(id)

Fetch 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.

A = astra_mex_data2d('get_single', id);

Fetch the data object as a 2D matrix of class single.

set / store

astra.data2d.store(id, A)

astra_mex_data2d('set', id, A)
astra_mex_data2d('store', id, A)

This stores the matrix A in the data object. The dimensions of A must match the dimensions of the existing data object.

Set and store are synonyms in the MATLAB interface.

get_geometry

geom = astra.data2d.get_geometry(id)

geom = astra_mex_data2d('get_geometry', id);

Get the (volume or projection) geometry attached to the object.

Note

The returned geometry may slightly deviate from the original geometry because of internal data type conversions.

change_geometry

astra.data2d.change_geometry(id, geom)

astra_mex_data2d('change_geometry', id, geom);

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

delete

astra.data2d.delete(id)

astra_mex_data2d('delete', id);

Free the memory of a data object.

clear

astra.data2d.clear()

astra_mex_data2d('clear');

Free all data objects.

info

astra.data2d.info()

astra_mex_data2d('info')

Print basic information about all allocated data objects.