The Refraction Filter Render Element is an image that stores refraction information calculated from the materials’ refraction values in the scene. Materials with no refraction values appear as black, while refractive materials appear as white (maximum refraction) or gray (lesser amounts of refraction). If any hue (color) is specified in the material’s Refractive Color parameter, that hue and value will be represented here in the Refraction Filter as well as being affected by the refraction’s Amount parameter.
In comparison, the V-Ray Raw Refraction Render Element is a color render element that takes materials and their colors into account when rendering refraction. Multiplying these two render elements together produces the V-Ray Refraction Render Element.
To properly calculate the Refraction Filter Render Element, the Refraction Render Element must also be added to the list of render elements being calculated during the rendering process to properly determine all the refraction information in the scene.