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Дата изменения: Mon Apr 18 23:42:54 1994 Дата индексирования: Sun Dec 23 19:34:20 2007 Кодировка: Поисковые слова: rings |
To illustrate the use of the algorithm to control noise amplification, we have
reconstructed a 256256 pixels planetary nebula simulation for the PC
camera prepared by R. Hanisch at ST ScI. The PSF has a similar radius to the
ring of the planetary nebula. The images combine background, a diffuse object,
and several bright stars. Fig. 1 (left) shows the raw image.
We have reconstructed the raw image using the FMAPEVAR algorithm with a space
variant parameter. We set
for the background,
for the diffuse planetary nebula and a high value for the
bright stars of
allowing the algorithm to reach maximum
likelihood in the stars.
Fig. 1 (right) shows the result of this three-channel restoration. We obtained a smooth background, a well reconstructed nebula, and sharp images of the stars. We suppressed the noisy amplification in the background and in the nebula, while fully developing the images of the stars.
In order to compare the new algorithm with the constant approach and
to study the photometric properties of the restoration, we made two
restorations of the raw image using a constant value of
and a
constant
respectively. Since this is a simulated image, we
can quantitatively study the restorations with respect to the true unblurred
image. For the restorations, we computed the percentage of energy recovered in
a 7
7 box located in the background, the ring, the central star and the
brightest star.
Fig. 2 shows the results. The restoration with constant only has correct photometry for the background. The restoration with
constant
performs well in the background and in the ring
(although the background is too noisy in the restoration) but the photometry is
poor in the stars because the stars are not properly developed. However, the
restoration with variable
in three channels performs much better in
the stars, while maintaining the quality the photometry in the ring and the
background. We obtained an accuracy better than 95%(or 0.05 mag.) for the
whole image. We adjusted the values of the variable
approximately
without any local cross-validation or segmentation. Thus, by using an optimum
adjustment it is possible to obtain even better photometry.