Add "Desaturate Background" to Filters

[prkos]

Please add a filter that when applied to an object, it makes the background behind the object show through but with colors desaturated.

Maybe it makes sense to add it under Color submenu, or possibly Overlay?

This was inspired by a forum post:
How to shine B&W background through a shape
http://www.inkscapeforum.com/viewtopic.php?p=93612#p93576

select the overlay shape. it should have a fill (any colour would do as long as it's not transparent)
go to filers/filter editor
new
add an fx : choose colormatrix and click add a fx
link color matrix to background-image
choose saturation as type in fx parameter

add a new fx: choose composite and click add a fx
the first node should be linked to color matrix by default ; don't change this.
link the second node to source image
chose "in" as operator

done

[Hachmann (marenhachmann)]

File with v1nce's filter in use (on a rectangle with a gradient).

[jazzynico (jazzynico)]

Interesting filter, thanks for the idea and the file!

[jazzynico (jazzynico)]

@Ivan, once again, we need you expertise on filters ;)
Any thought on that new filter request? Is it something we can already do with the existing filters? If not, do you think we should keep it simple or add some parameters?
Thanks!

[ivan louette (ivan-louette)]

@jazzynico, the proposed filter seems excellent. However "Enable Background" should be activated in the default template to allow it to work. And this is not the case at the moment in trunk.