Basic Use

Inkscape » Filter Effects—Custom » Basic Use

Filters can be defined and applied through the Filter Effects dialog. The Gaussian Blur filter can also be used directly through the Fill and Stroke dialog. The Blend filter can also be applied to an entire Layer through the Layers dialog.

The Fill and Stroke dialog has a Blur slider that when moved from zero, creates and attaches a Gaussian Blur filter to selected objects. If the slider is reset to zero, the filter is automatically removed and deleted. The same principle works on the Layers dialog where a choosing anything but Normal creates a Blend filter and attaches it to the Layer. Setting the drop-down menu back to Normal deletes the filter. Filters can also be removed from an object by using the menu entry Filters → Remove Filters.

The Filter Effects dialog (Filters → Filter Editor...) is used to build complex Filters out of Filter primitives. An example of a complex Filter is the “Drop-Shadow” filter. The dialog is also used to apply Filters to objects.

The source of the graphic used as an input for a Filter primitive is either the output of another Filter primitive or one of the following sources:

Source Graphic. Use the object as the source for the Filter primitive.
Source Alpha. Use the Alpha of the object as the source for the Filter primitive.
Background Image. Use the region under the Filter at the time the Filter is invoked.
Background Alpha. Use the Alpha of the region under the Filter at the time the Filter is invoked.
Fill Paint: Not implemented. Use the Fill of the target object as the input to a Filter primitive as if the object had an infinite extent. Useful if the Fill is a Gradient or Pattern with transparent or semitransparent regions.
Stroke Paint: Not implemented. Use the Stroke of the target object as the input to a Filter primitive (see Fill Paint above).

	Need to add “enable-background” tag!
Whenever an input to a Filter is specified to be Background Image or Background Alpha, the SVG file must include the “enableBackground” tag to tell the SVG renderer it must keep a copy of the background around. Inkscape does not add this tag for you except in the case of using the Layer dialog to add a blend. A work-around is to use the Layer dialog to temporarily add and then remove a Blend filter; this will leave the necessary tag in place.

Need to add “enable-background” tag!

Whenever an input to a Filter is specified to be Background Image or Background Alpha, the SVG file must include the “enableBackground” tag to tell the SVG renderer it must keep a copy of the background around. Inkscape does not add this tag for you except in the case of using the Layer dialog to add a blend. A work-around is to use the Layer dialog to temporarily add and then remove a Blend filter; this will leave the necessary tag in place.

A filter effect is applied to a region defined relative to the object to which it is attached. By default, the Filter Effects Region ranges from −0.1 to 1.1 in units of the object's bounding box width and height. This area may not always be sufficient. For example, if a large shift is prescribed in the Offset filter, the area must be increased. The area can be adjusted under the Filter General Settings tab of the Filter Effects dialog. (It can also be set through the XML Editor dialog, attributes x, y, width, and height.)

The default Filter Effects Region is shown for the red circle.

The Filter Effects Region can be defined in terms of the object's bounding box or by units in the current user coordinate system by setting the “filterUnits” parameter to “objectBoundingBox” or “userSpaceOnUse”. Inkscape currently supports only the use of the first in the GUI.

	Color Space For Filters
	Inkscape uses the sRGB color space with filters. The SVG standard specifies that by default, the linearRGB color space should be used. This is a known problem with Inkscape. If you wish your drawings to look the same in other SVG renderers, you need to manually add the attribute `color-interpolation-filters="sRGB"` to the <filter> tag. (This is already done for the prebuilt filters.)