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wiener stsdas.analysis.restore


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SEE_ALSO

NAME

wiener -- Noniterative Fourier deconvolution filter (2-D)

USAGE

wiener input psf output

DESCRIPTION

This task applies a Fourier noniterative deconvolution filter to 2-dimensional images. The filter form may be chosen among inverse, Wiener, geometric mean and parametric types. (Type "help wiener opt=sys" to see a more detailed explanation of filter characteristics, limitations, and usage.) You may use the task with its default parameter settings, supplying only the required parameters. However, to fully exploit the task capabilities (and hopefully achieve better restorations), reading the opt=sys help pages is recommended.

Psets are used to input information to the task. There are separate psets dedicated to the Point Spread Function (PSF), filter parameters, signal model parameters, noise parameters and an optional low-pass filter.

The PSF can be input from either a separate file, or from the input image to be deconvolved. In either case, the PSF need not be centered in the field. You may specify the center coordinates px0 and py0 of the PSF in the PSF image section, or, leaving either one, or both, as INDEF, instructing the task to find them automatically. In this case, the pixel with maximum intensity in the PSF image section will be taken as the PSF center. A circular mask with low leakage can be used to isolate a suitable star in a crowded field. The radius is specified by task parameter mask (in pixels), and must be wide enough to not affect the point source image, but narrow enough to eliminate field stars. The PSF must be background-subtracted before using it with this task. When extracting the PSF directly from the input image, this image must have the background already subtracted.

Besides the PSF, the Wiener filter needs additional information about the undegraded image and noise statistics. This information is derived using the signal model and noise parameters in the corresponding psets. The meaning of these parameters is described in detail in the system-level help by typing "help wiener opt=sys".

After deconvolving the input image, the task may optionally apply a low-pass filter to the deconvolution result. This low-pass filtering step is particularly important in the case of inverse filter deconvolution. Use task parameter lowpass in the appropriate pset to specify filter type, and fwhm parameter to specify the width of the smoothing kernel in image pixel units. A circularly symmetric or an axially symmetric (in frequency domain) filter can be selected, or you can specify that no filter is to be used at all. The square filter has proven to be effective at eliminating rings around the deconvolved point sources. The filter is an apodizing function which minimizes side-bands.

The output deconvolved image is normalized to the same total flux as in the input image.

Any image size and aspect ratio may be used as input for this task. The input and PSF images may have different size axis. However, for efficiency purposes, the input image axis sizes must be even. If the input image contains an odd-size axis, the last row or column will be stripped off. The Fast Fourier Transform algorithm used by this task is faster when the axis sizes are composite numbers (i.e., non-primes), faster yet when rich in factors of 2, and even faster with exact powers of 2. One limitation in input image size may come from the amount of memory available to the task. For a 512 X 512 image, the task will use about 5 MB of memory for data storage.

The filter function itself can optionally be written to an output image file. This image will contain the amplitude squared of the complex filter function, eventually multiplied by the low-pass filter function. The filter task parameter specifies the file name to be created; if left as a null string (""), no filter output is generated. Similarly, if task parameter output is set to null, then no deconvolved image is generated. This option saves some execution time, and is useful when running the task repeatedly, for example, when you are interested in the filter function form only.

The task can process an image template or list of files passed to input. In this case, output is either a matching list of images or a directory. Both psf and filter must be always single images.

History records with filter parameter information are appended to the output image header.

Typical CPU times (Sparc 2, 512 X 512 image): 45 sec for inverse filter; 90 sec for geometric mean filter with external image signal model.

PARAMETERS

input [file name template]
Input 2-dimensional image(s) section(s) to be deconvolved. This may optionally be a list of files to be processed.
psf [file name]
Input PSF 2-dimensional image section.
output [file name]
File name for the output deconvolved image(s). This parameter will also take the name of a directory. If left as a null string (""), no output is produced. Output images are always of type real, regardless of input image type.
(filter = "") [file name]
Output filter image. If left as a null string (""), no filter image is produced.
(psfpars) [pset]
Pset with PSF parameters:
(nlpsf = yes) [boolean]
Is the PSF noiseless? If the PSF is taken from an observed image, this parameter must be set to "no", in which case, a "prunning" filter will be used in processing the PSF image. If the PSF is synthetic and without noise, this parameter must be set to "yes".
(px0, py= INDEF) [real, min=1.]
Center coordinates, in pixels, of PSF in psf image section. If either one, or both, are left as INDEF, the task will locate the maximum pixel value in the PSF image section, and use its coordinates instead.
(mask = INDEF) [real, min=1.]
PSF masking radius, in pixels. If INDEF, no masking is performed.
(filterpars) [pset]
Pset with filter parameters:
(ftype = Wiener) [string, allowed values: Wiener | inverse |
parametric | geometric]

Filter type to be used.

(gamma = 1.) [real, min=0.]
When using parametric filter form, this is the constant value. Not used in other filter forms.
(modelpars) [pset]
Pset with signal model parameters:
(signalm = input) [string, allowed values: white | input |
Markov | Gaussian | psf | image file name]

Theoretical (undegraded) signal model to be used in Wiener and geometric mean filter forms. When none of the first five options is entered, the task attempts to open and read an IRAF image with the name given by the signalm parameter.

(correl = 2.) [real, min=0.]
Correlation factor to be used when the undegraded signal model is to be estimated from the input degraded image itself (i.e., when signalm=input). If set as INDEF, signal model will be computed from input and psf images.
(mfwhm = 2.) [real]
Model Gaussian FWHM. Used when the undegraded signal model is a Gaussian.
(noisepars) [pset]
Pset with noise parameters:
(statistic = independent) [string, allowed values: independent | Poisson]

Noise model.

(fnoise = INDEF) [real, min=1.]
Frequency, in frequency domain pixels, where the task will measure the noise power spectral density. If INDEF, the highest available frequency is used (recomended).
(lowpars) [pset]
Pset with low-pass filter parameters:
(lowpass = "none") [string, allowed values: none | square | circular]

Type of low-pass filter.

(fwhm = INDEF) [real, min=1.]
Full width at half maximum of low-pass filter smoothing kernel, in image pixel units. If INDEF, no filtering is performed regardless of lowpass value.
(verbose = no) [boolean]
Print file names and execution times?

EXAMPLES

BUGS

REFERENCES

This task was written by I.Busko

SEE ALSO

Type "help wiener opt=sys" for more information about this task.


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