Photoshop Filters and Forests

Hi
When I look at some of the amazing community maps that people have done I often see them mention they used a photoshop filter or Gimp filter etc, but never say what the filter was. Can people suggest good filters to use on maps to give them an old style look.
Forests, I like to use the Herwin Wielink style a lot but I do not like the Forest fill, (similar to 13th Age style and hating the Mountains) can anyone recommend a Forest Fill style that would work with Herwin Wielink style.
Thanks
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