The Set Background/Create Stencil function was performed to simultaneously set this picture of a sidewalk, people, puddle, etc. as the Mask Background and also create a stencil based on the lightness/darkness of the same image.  A photo of a lamp behind a lacy curtained window was then loaded and a Kaleider Split Oval Funnel was rendered.  This image illustrates Masking with the Mode set to Blend, which caused the Background image to merge translucently with the rendered pattern, blending elements according to degrees of lightness/darkness.  Using On/Off Mode, on the other hand, would produce sharply defined regions that are either totally opaque or entirely transparent.