This is the Frei0r sigmoidaltransfer MLT filter by Janne Liljeblad.
Desaturates image and creates a particular look that could be called Stamp, Newspaper or Photocopy.
Brightness: Controls Brightness of image. Range 0 to 1.
Sharpness: Controls sharpness of transfer. Range 0 to 1.
Both parameters default to 0 in Kdenlive - which is unfortunate because this results in a totally black frame. You need to have numbers above zero to see the effect.