feMerge Filter Element¶
This filter primitive composites input image layers on top of each other using the over operator with Input1 (corresponding to the first feMergeNode child element) on the bottom and the last specified input, InputN (corresponding to the last feMergeNode child element), on top.
Many effects produce a number of intermediate layers in order to create the final output image. This filter allows us to collapse those into a single image. Although this could be done by using n-1 Composite-filters, it is more convenient to have this common operation available in this form, and offers the implementation some additional flexibility.
Each feMerge element can have any number of feMergeNode subelements, each of which has an in attribute.
The canonical implementation of feMerge is to render the entire effect into one RGBA layer, and then render the resulting layer on the output device. In certain cases (in particular if the output device itself is a continuous tone device), and since merging is associative, it might be a sufficient approximation to evaluate the effect one layer at a time and render each layer individually onto the output device bottom to top.
If the topmost image input is
'SourceGraphic' and this feMerge is the
last filter primitive in the filter, the implementation is encouraged to render
the layers up to that point, and then render the SourceGraphic directly from its
vector description on top.
For common properties see: Filter Primitives Overview
Parameters: layernames (list) – layernames as strings
Create a feMerge filter, containing several feMergeNode subelements, with the input sources specified by layernames.