The Raw Refraction Render Element is a color image that stores refraction information calculated from materials’ refraction values in the scene. Surfaces with no refraction values set in their materials will contain no information in the render element and therefore will render as black.
In comparison, the Refraction Filter Render Element is a render element that indicates varying degrees of refraction in the scene through brightness values in the image. Multiplying these two render elements together produces the V-Ray Refraction Render Element .
Note: To properly calculate the Raw Refraction 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.