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Дата изменения: Fri Jan 10 22:48:37 2003
Дата индексирования: Sat Dec 22 08:11:29 2007
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XMM-Newton Science Analysis System


asmooth (asmooth-2.10.2) [xmmsas_20030110_1802-5.4.1]

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Description

This task performs adaptive smoothing of FITS images. It has two purposes: firstly, the cosmetic purpose of smoothing out grainy backgrounds; secondly, as an alternative to esplinemap for producing background maps.

Although the task was designed with EPIC X-ray images in mind, it makes few requirements of the input files and can be used to smooth any FITS image in the appropriate data format (see section 6).

The task employs truncated gaussian smoothing kernels of the form

$$K_{i,j} = \frac{k_{i,j}}{\sum_{i=-N}^{N} \sum_{j=-N}^{N} k_{... ...rt i\vert \le N$\ and $\vert j\vert \le N$, $K_{i,j}=0$\ else}$$

where

$$k_{i,j} = exp\left(-\frac{i^{2} + j^{2}}{2\sigma^{2}}\right)\rm {.}$$ (1)

Here $i$ and $j$ are the distances in pixels from the centre of the gaussian and the units of $\sigma$ (although non-integer) are also pixels. $N$ is set equal to $1 +$floor($5 \sigma$).

The value of $\sigma$ can either be kept constant over the extent of the image to produce uniform, non-adaptive smoothing (parameter smoothtype = `simple') or can be made different at different parts of the image (smoothtype = `adaptive').