7.38. Threshold Alpha

7.38. Threshold Alpha
	7. The “Layer” Menu

The Threshold Alpha command converts semi-transparent areas of the active layer into completely transparent or completely opaque areas, based on a threshold you set. It only works on layers which have an alpha channel. If the Lock alpha channel option is checked in the Layers dialog, the filter will have no effect.

7.38.1. Activating the Command

You can access this command from the menubar through Layer → Transparency → Threshold Alpha....

7.38.2. Description of the Dialog Window

图 16.121. The “Threshold Alpha” filter options dialog

Presets, Input Type, Blending Options, Preview, Split view

	注意
	These options are described in 第 2 节 “Common Features”.

Value

The threshold alpha value determines which values will become transparent or opaque. You can set the transparency value to be used by using the slider or by entering a value between 0 and 1 in the input box. All transparency values above this threshold will become opaque and all transparency values below or equal to this threshold will become completely transparent.

	注意
	This command will never make completely transparent pixels (alpha value = 0) opaque.

图 16.122. Threshold Alpha example

A transparency gradient 0-255.

Threshold set to 50, 127, 210.