2D Data Objects

astra_mex_data2d

astra_mex_data2d is used to manage 2D data objects. It is a wrapper around the MEX file astra_mex_data2d_c.

2D data objects come in two varieties: volume data and projection data (sinograms).

astra_mex_data2d contains the following commands.

  • create

  • link (python)

  • get

  • get_shared (python)

  • get_single (matlab)

  • set / store

  • get_geometry

  • change_geometry

  • delete

  • clear

  • info

  • shepp_logan (python)

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.

link

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

Creates an Astra data object that shares its memory with the specified numpy.ndarray. The ndarray must be contiguous, have float32 dtype, and be of the right shape. Changes to the ndarray will be visible to Astra, and vice versa. This increments the reference count of the underlying memory, so it is safe to delete the linked ndarray while the Astra object still exists.

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

N/A

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

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

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