Green-controls the level of green to be subtracted from the image.Type directly in the text box or drag the slider to set the value. Red-controls the level of red to be subtracted from the image.Grey-controls the level of gray to be subtracted from the image.Radius-controls the distance from which color is sampled around the handle, up to a maximum of 20 px.Sample color at handle-when selected (recommended), the gray and RGB levels for the selected handle are automatically read from the handle's position.The following settings can be adjusted in the filter dialog:

Manually setting any of these values will cause Sample color at handle to become deselected for the selected handle. caused by light pollution, sky glow or moon illumination.Īlternatively, specify your own gray and RGB levels for subtraction by selecting a handle and manually setting the filter's Grey, Red, Green and Blue values. Click within the document view to create additional handles to remove gradients, e.g. Use a single handle to remove a fairly uniform background. Drag it to reposition as needed to sample a background tone to be subtracted. The filter is destructive, so it is recommended to apply it to a merged pixel layer that is created after tone-stretching but before any other post-processing has been applied to your image.Ī color-sampling handle is precreated at the center of the image. This filter can be found in the Filters menu, in the Astrophotography category.

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