| Algorithm |
Description |
Advantages |
Disadvantages |
| Back
Projection |
Most basic method of image reconstruction.
Multiplies the calibrated event list by the collimator modulation patterns
to construct a 'dirty map' of the image. |
Very fast. Linear. Simple. |
Poor quality images with sidelobes. No
reliable source sizes. |
| Clean |
Iteratively identifies peaks in the back
projection map and removes contributions from the associated sources
convolved with the Point Spread Function. The reconstructed image is
the sum of Gaussians based on the point source fluxes. |
Relatively fast. Positive fluxes. Removes
sidelobes. |
Prone to photometric errors. Likely to
misinterpret extended sources. |
| Forward Fit |
Assumes the source(s) can be presented as a
simple functional form with a few free parameters (for example, a circular
Gaussian source) and looks for the parameters that produce a map that
is consistent with the data. |
Fast. Positive fluxes. Provides
source sizes and errors on parameters. |
Requires that assumptions concerning the number
of sources and their shapes are accurate. |
| Pixon |
Seeks a superposition of circular sources or
pixons of different sizes and parabolic profiles that best reproduces the
measured modulations from the different detectors. The goal is to construct
the image with the fewest degrees of freedom (the fewest pixons) that is
consistent with the observations. |
Robust. Accurate image photometry. Best
method to image extended sources in the presence of compact sources. |
Slow. Subjective smoothing required to avoid
source breakup at high resolution. |
| MEM NJIT |
Maximum Entropy Method algorithm based on
visibilities. This is a 2-D version of radio astronomy's SSMEM
provided by NJIT. |
Fast. Accurate image photometry and
morphology. Capable of super-resolution. |
Subject to source breakup when using data from
the finest grids. |
| VIS FWDFIT |
Forward-fit algorithm based on visibilities.
Like the Forward-Fit algorithm, assumes there are a limited number of simple
individual sources that can be parameterized. Adjusts the source
parameters such that the model-predicted visibilities agree best with the
measured visibilities. |
Fast. Provides uncertainties on source
parameters. |
Requires that assumptions concerning the number
of sources and their shapes are accurate. Currently limited to one or
two circular or elliptical Gaussians, or a single loop. |
| UV
SMOOTH |
Performs a Fast Fourier Transform of 2-D spline-interpolated
visibilities. |
Fast. Good photometry. |
Vulnerable to missing visibilities. |
| MEM Sato
(no longer supported) |
Maximum Entropy Methods (MEM) algorithm finds
the 'most plausible' solution which has the maximum configuration entropy
among those solutions that are consistent with the observation. |
Relatively fast. Positive fluxes. |
Unsupported. |
| MEM Vis
(no longer supported) |
Similar to MEM Sato, except works with
visibilities instead of counts. |
Relatively fast. Positive fluxes. |
Unsupported. |
