An adaptive filter for processing of astronomical images is developed and described. The filter recognizes the local signal resolution (which usually varies strongly across the image) and adapts its own impulse response to this resolution.
This study reports on the results of the application of an adaptive filtering technique to the two-dimensional photometric mapping of galaxies. For this test we used the elliptical galaxy NGC 3379, which is a luminosity standard. Our plate material (B-band), obtained with the Tautenburg Schmidt telescope, was digitized with the Babelsberg microdensitometer and with the ESO PDS. The 2-D scans were reduced according to the Babelsberg Image Processing Systems, whose key feature is an adaptive filter called 'H-Transform'. By comparing our results (E-Wlight profile and isophotal parameters) to the most recent studies of NGC 3379 CAPACCIOLI 1979, and NIFTO andVIDAL 1984), we found no systematic errors in the photometric calibration and in the reduction procedure, with typical mean residuals from the other studies not larger than 0.05 B-mag up to a threshold of 1 % of the night sky level on each plate. We also re-confirmed the geometrical properties of the galaxy. The new filtering technique proved quite efficient in reducing the noise, with negligible effects on the photometric and geometric characteristics of the star-like sources.Die Ergebnisse einer adaptiven Filterung meidimensionaler Bilder zur photometrischen Untersuchung von Galaxien werden mitgeteilt. Die mit dem Tautenburger Schmidtteleskop aufgenommenen Photoplatten der elliptischen Galaxie NGC 3379 wurden am Flachenphotometer der Sternwarte Babelsberg und am PDS der Europaischen Siidsternwarten ESO abgetastet. Die Datenauswertung erfolgte mit Hilfe des Babelsberger Programmsystems zur Bildverarbeitung, das ein adaptives Filtersystem auf der Basis der H-Transformation realisiert. Unsere Ergebnisse wurden mit den Messungen der photometrischen Standard-Galaxie NGC 3379 CAPACCIOLI 1979, NIETO andVIDAL 1984) verglichen. Die photometrische Eichung der Platten und die Auswertungsmethodik sind frei von systematischen Fehlern und zeigen mittlere Abweichungen von kleiner als 0.05 mag bis zum 1 % Niveau der Nachthimmelshelligkeit auf den untersuchten Platten. Wir bestatigen die geometrischen Eigenschaften der Galaxie.
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