Made a new template file with this wave pattern:
To suit the pattern, made some tracing of Japan related images.
Figure of speech because for the actual tracing I used the online upload option of openclipart -potrace at openclipart.com.
Haven't seen the svg-s they generated, but probably they have 100000+nodes.
As they generate inkscape made svg-s thumbnails with inkscape 0.91, some previous attempts had thumbnail issues -missing- so it's also a safe bet that they may not render best inside inkscape at the moment.
Anyway, the process was the following:
opening this template
importing a raster image from pixabay,
resizing it if necessary to a roughly 4800 px/3600 px size -not really necessary-
and creating a raster copy (Alt+B) and deleting both images.
This results creating a raster image with the filter flattened inside the svg's folder, which then I uploaded to the mentioned potrace site.
Still rendering the raster copy took some time.
Here are a few examples:
Maybe the filter should be tweaked so that the full black/white tones wouldn't cause unfilled/flooded areas.