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Photons interact with an object by some combination of reflection, absorption and transmission. Some materials, such as plate glass and clean water, transmit much of the light that falls on them and reflect little of it; such materials are called optically transparent. Many liquids and aqueous solutions are highly transparent.
By using two parabolic cylindric mirrors and one plane mirror, the image of the background is directed around an object, making the object itself invisible - at least from two sides. Invisibility is the state of an object that cannot be seen. An object in this state is said to be invisible (literally, "not visible").
An opaque object is neither transparent (allowing all light to pass through) nor translucent (allowing some light to pass through). When light strikes an interface between two substances, in general, some may be reflected, some absorbed, some scattered, and the rest transmitted (also see refraction ).
Because it is often transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window panes, tableware, and optics. Some common objects made of glass are named after the material, e.g., a "glass" for drinking, "glasses" for vision correction, and a "magnifying glass".
Incidentally, this also makes the objects completely transparent when the viewpoint camera is located inside them, because then all the surfaces of the object are facing away from the camera and are culled by the renderer. To prevent this the object must be set as double-sided (i.e. no back-face culling is done) or have separate inside surfaces.
Some image formats, such as PNG and TIFF, also allow partial transparency through an alpha channel, which solves the edge limitation problem. Instead of each pixel either being transparent or not transparent, it can be set to 254 levels of partially transparent, allowing some of the background image to show through the foreground image.
Objects don’t have feelings, but some people treat them like they do. It’s called anthropomorphizing, and it’s natural to do to objects and animals, experts say.
The usual result is a negative shadow image that shows variations in tone that depends upon the transparency of the objects used. Areas of the paper that have received no light appear white; those exposed for a shorter time or through transparent or semi-transparent objects appear grey, [1] while fully-exposed areas are black in the final print.