SIRT
====

This is a CPU implementation of the Simultaneous Iterative Reconstruction Technique (SIRT) for 2D data sets. It takes projection data and an initial reconstruction as input, and returns the reconstruction after a specified number of SIRT iterations.

Supported geometries: parallel, parallel_vec, fanflat, fanflat_vec, matrix.

Configuration options
---------------------

=============================== ========	==================================================================================================================================================
name 				type 		description
=============================== ========	==================================================================================================================================================
cfg.ProjectorId 		required 	The astra_mex_projector ID of the projector.
cfg.ProjectionDataId 		required 	The astra_mex_data2d ID of the projection data
cfg.ReconstructionDataId 	required 	The astra_mex_data2d ID of the reconstruction data. The content of this when starting SIRT is used as the initial reconstruction.
cfg.option.SinogramMaskId 	optional 	If specified, the astra_mex_data2d ID of a projection-data-sized volume to be used as a mask.
cfg.option.ReconstructionMaskId optional 	If specified, the astra_mex_data2d ID of a volume-data-sized volume to be used as a mask.
cfg.option.MinConstraint 	optional 	If specified, all values below MinConstraint will be set to MinConstraint. This can, for example, be used to enforce non-negative reconstructions.
cfg.option.MaxConstraint 	optional 	If specified, all values above MaxConstraint will be set to MaxConstraint.
=============================== ========	==================================================================================================================================================

Example
-------

.. tabs::
  .. group-tab:: Python
    .. code-block:: python

      import astra
      import matplotlib.pyplot as plt
      import numpy

      # create geometries and projector
      proj_geom = astra.create_proj_geom('parallel', 1.0, 256, numpy.linspace(0, numpy.pi, 180, endpoint=False))
      vol_geom = astra.create_vol_geom(256,256)
      proj_id = astra.create_projector('linear', proj_geom, vol_geom)

      # generate phantom image
      V_exact_id, V_exact = astra.data2d.shepp_logan(vol_geom)

      # create forward projection
      sinogram_id, sinogram = astra.create_sino(V_exact, proj_id)

      # reconstruct
      recon_id = astra.data2d.create('-vol', vol_geom, 0)
      cfg = astra.astra_dict('SIRT')
      cfg['ProjectorId'] = proj_id
      cfg['ProjectionDataId'] = sinogram_id
      cfg['ReconstructionDataId'] = recon_id
      cfg['option'] = { 'MinConstraint': 0, 'MaxConstraint': 1 }
      sirt_id = astra.algorithm.create(cfg)
      astra.algorithm.run(sirt_id, 100)
      V = astra.data2d.get(recon_id)
      plt.gray()
      plt.imshow(V)
      plt.show()

      # garbage disposal
      astra.data2d.delete([sinogram_id, recon_id, V_exact_id])
      astra.projector.delete(proj_id)
      astra.algorithm.delete(sirt_id)


  .. group-tab:: Matlab
    .. code-block:: matlab

	%% create phantom
	V_exact = phantom(256);

	%% create geometries and projector
	proj_geom = astra_create_proj_geom('parallel', 1.0, 256, linspace2(0,pi,180));
	vol_geom = astra_create_vol_geom(256,256);
	proj_id = astra_create_projector('linear', proj_geom, vol_geom);

	%% create forward projection
	[sinogram_id, sinogram] = astra_create_sino(V_exact, proj_id);

	%% reconstruct
	recon_id = astra_mex_data2d('create', '-vol', vol_geom, 0);
	cfg = astra_struct('SIRT');
	cfg.ProjectorId = proj_id;
	cfg.ProjectionDataId = sinogram_id;
	cfg.ReconstructionDataId = recon_id;
	cfg.option.MinConstraint = 0;
	cfg.option.MaxConstraint = 255;
	sirt_id = astra_mex_algorithm('create', cfg);
	astra_mex_algorithm('iterate', sirt_id, 100);
	V = astra_mex_data2d('get', recon_id);
	imshow(V, []);

	%% garbage disposal
	astra_mex_data2d('delete', sinogram_id, recon_id);
	astra_mex_projector('delete', proj_id);
	astra_mex_algorithm('delete', sirt_id);