Blacklevel compensation is only available on Pandoras Box Servers.
For blacklevel compensation layers are needed that are not included in the first render pass, the composition pass (the render passes are explained in the topic Video Processing Pipeline ). To exclude a layer from the composition pass, check the radio button "Output" in the layer's Inspector. This layer is now not affected by the output settings in regards to warp object, keystone and softedge settings.
Use the layer with effects that suit your need (area-coloring or black lifting colors), e.g Gradient or Shapes FX. There are effects available, e.g. triangle and square gradients / shapes, to set up a geometry that matches exactly the shape needed. The different overlapping types are depicted in the above image. In addition, the shapes can be adjusted with different colors per corner. This is important when working with projectors that show a gradient due to lens errors or worn out lamps.