In architecture, a gargoyle is a carved stone grotesque with a spout designed to convey water from a roof and away from the side of a building. Preventing rainwater from running down masonry walls is important because running water erodes the mortar between the stone blocks. Architects often used multiple gargoyles on buildings to divide the flow of rainwater off the roof to minimize the potential damage from a rainstorm. A trough is cut in the back of the gargoyle and rainwater typically exits through the open mouth. Gargoyles are usually an elongated fantastic animal because the length of the gargoyle determines how far water is thrown from the wall. When Gothic flying buttresses were used, aqueducts were sometimes cut into the buttress to divert water over the aisle walls.
Chroma key compositing, or chroma keying, is a special effects / post-production technique for compositing (layering) two images or video streams together based on color hues (chroma range). The technique has been used heavily in many fields to remove a background from the subject of a photo or video – particularly the newscasting, motion picture and videogame industries. A color range in the foreground footage is made transparent, allowing separately filmed background footage or a static image to be inserted into the scene. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as color keying, colour-separation overlay (CSO; primarily by the BBC), or by various terms for specific color-related variants such as green screen, and blue screen – chroma keying can be done with backgrounds of any color that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from most human skin colors. No part of the subject being filmed or photographed may duplicate the color used as the backing.