16. Filtres Canal alfa a logotip

16. Filtres Canal alfa a logotip
	Capítol 17. Filtres

16.1. Introducció

Figura 17.369. Menú dels filtres Canal alfa a logotip

These filters correspond to the logo-generating Script-Fu scripts. They add all kinds of special effects to the alpha channel of the active layer (that is, to the pixels with a non-zero alpha value).

	Nota
	The menu items and the corresponding functions are enabled only if the active layer has an alpha channel. If you see that the menu items are grayed out, try to add an alpha channel.

The filter effect will always be applied according to the alpha values. The alpha of any pixel has a value ranging from 0 (transparent) to 255 (fully opaque). It is possible to apply a filter only partially to some (or all) pixels by using alpha values from 1 to 254.

You will notice that this is similar to selecting pixels partially. In fact, internally these filters always create a selection from the alpha channel by transferring the alpha values to the channel which represents the selection, and then work on the selection.

How to apply an “Alpha to Logo” filter to a selection?

If the active layer is the background layer, make sure that an alpha channel exists, otherwise add an alpha channel.

	Suggeriment
	If a layer name in the Layer Dialog is in bold, then this layer has no Alpha channel.

Inverteix la selecció: Selecciona → Inverteix.
Remove the (inverted) selection: Edit → Clear.
Aplica el filtre “Canal alfa a logotip” (els filtres ignoren la selecció, per tant no us cal tornar a revertir-la).