This is a somewhat experimental option which allows you to apply a texture to to final wallpaper by modifying the lightness of the image according to the lightness of a texture image. The texture image is tiled across the surface of the processed image.
The sliders are used to vary the effect. The default settings are a good starting point for most textures. Just experiment with the settings to get the best result depending on your chosen texture file.
(Note: all credit for the texturising process lies with Steve McMahon at vbaccelerator.com)