Magentakorrektur-Filter
This is a cosmetic filter designed to reduce the effect of purple fringing around stars that may be visible when using an achromat refractor especially when broadband imaging. It operates on stretched colour images.
Tipp
Dieser Filter ist für die Bearbeitung nichtlinearer Bilder ausgelegt. Daher muss er unbedingt nach der Streckung des Histogramms angewendet werden.
Der Filter bietet zwei Modi an, die seine Wirkung nur auf Sterne limitieren oder auf alles anwenden.
It reduces purple fringing by applying a luminance mask to the blue channel based on the green channel, and by allowing you to reduce the blue channel intensity. When in starmask mode, it limits the effects to areas around identified stars.
Global
Dieser Modus ist nützlich, wenn man mit einer Sternmaske oder einem Bild arbeitet, das nur Sterne enthält, beispielsweise ein Kugelsternhaufen. Er ist nicht so nützlich für Nebel oder Bilder von Galaxien, in denen die Farbe verändert dadurch werden könnte.
To use, you should reduce the Blue Adjustment slider until the effects are optimal. This is generally around 0.15.
You may also increase the Threshold slider to restrict the effects to those pixels where the luminance is above this value. In this mode, the optimal value will be quite low.
Sternenmaske
Dieser Modus ist nützlich, um bei kombinierten Bildern den Effekt dieses Filters nur auf Sterne zu begrenzen.
To use, you should tick Use Starmask. If you've not already defined a starmask using the Dynamic PSF function, there will be a delay of a few seconds whilst the starmask is generated. You may now temporarily reduce the Blue Adjustment to zero. Your stars should now be yellow. If you still see purple fringing, you should increase the Threshold slider until the fringing is entirely covered by yellow. Now you can increase the Blue Adjustment slider until your stars are not yellow but your purple fringing is reduced or eliminated, typically around 0.12-0.15.
Comparison before/after application of the unpurple filter. We can see very clearly that the stars have a better color, without the purple ring.
Siril Kommandozeile
unpurple [-starmask] [-blue=value] [-thresh=value]