The Reflection Filter Render Element stores reflection information calculated from the materials' reflection values reflection values in the scene. Surfaces with no reflection values set in its material(s) will contain no information in the render pass and will therefore render as black.
While the vrayRE_Raw_Reflection Render Element gives the full reflection of objects reflecting in the scene, vrayRE_Reflection_Filter shows how much of that reflection should come through in the composite. In other words, the filter defines the strength of the reflection, while the raw image defines what is being reflected in the image. When these two elements are multiplied, the true level of reflection is given and produces vrayRE_Reflection. Using these component parts of the reflection, you can better fine tune the reflection in your final composite.
Reflection element is a key component in the main Beauty Pass.
To use render elements, select from the Available render elements column and click the Add button to add the passes you wish to generate at render time. When you render the scene, the added render elements listed in the column on the right, will also render, which can be viewed from the VFB window's channel drop-down menu.
For more information on the parameters on this dialog, see the Render Elements tab page.
