I use MapProxy for caching WMS/WMTS tiles and it works fine up to a certain zoom level. But for higher zoom levels MapProxy fills the empty parts of the layers in black. This happens for certain geometries, mostly polygons where I only showe their stroke but they have an empty fill.
It seems to be a problem with transparencies as the white parts also should be transparent. I define transparent true at the sources configuration in mapproxy.yaml:
sources: test_wms: type: wms req: url: http://qgis-server.com/service? layers: Test WMS transparent: true
I additionally tried (without success) to define a global format and use in in cache:
globals: image: formats: imgformat: format: image/png mode: P transparent: true
Another test was to add the image parameter to the layer source configuration:
image: transparent_color: '#ffffff' transparent_color_tolerance: 0