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FASTMED-Applies a square median filter of user defined size to an input
image
- Description:
The method used employs a rolling histogram and allows
the whole image to be filtered.
The median pixel value in the region surrounding each input
image pixel is calculated. This value is then subtracted from
the value of the pixel being considered. Finally, the original
background count is added to the result, which is placed in the
corresponding pixel of the output image.
- Usage:
FASTMED IN OUT BACK SIGMA WIDTH
- Parameters:
-
BACK = _REAL (Read)
-
Image background count value. Units counts.
-
IN = _NDF (Read)
-
The name of the NDF to which the filter will be applied.
-
OUT = _NDF (Write)
-
The name of the output NDF that will be created.
-
SIGMA = _REAL (Read)
-
Standard deviation of the background count value. Units counts.
-
WIDTH = _INTEGER (Read)
-
The width of the filter to be employed. Units pixels.
- Examples:
-
fastmed in=field out=flatgal back=760. sigma=27. width=72
-
In this example, a 72x72 pixel filter will be applied to
the input image FIELD. The resulting median filtered image
will be placed in output image FLATGAL. The input image
(FIELD) had a global background count value of 760 with
an associated standard deviation of 27 counts.
- Notes:
With small filters it may be found that the resulting output
images are noisy. This is due to the small
number of pixels contributing to the histogram. The problem will
be most obvious at the image edges and corners. For this reason
some users may find it necessary to clip the output image by
WIDTH/2 pixels on each edge to generate better results.
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Up: Description of the ESP routines
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ESP --- Extended Surface Photometry
Starlink User Note 180
Norman Gray
Mark Taylor
Grant Privett
27 January 2000
E-mail:ussc@star.rl.ac.uk
Copyright © 2002 Council for the Central Laboratory of the Research Councils