In photography, a negative may refer to three different things, although they are all related.
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Film for 35 mm cameras comes in long narrow strips of chemical-coated plastic. As each image is captured by the camera onto the film strip, the film strip advances so that the next image is projected onto unexposed film. When the film is developed it is a long strip of small negative images. This strip is often cut into sections for easier handling. In larger cameras this piece of film may be as large as a full sheet of paper, or even larger, with a single image captured onto one piece. Each of these negative images may be referred to as a negative and the entire strip or set of images may be collectively referred to as negatives. These negative images are the master images, from which all other copies will be made, and thus they are treated with care.
A positive image is a normal image. A negative image is a tonal inversion of a positive image, in which light areas appear dark and vice versa. A negative color image is additionally color reversed, with red areas appearing cyan, greens appearing magenta and blues appearing yellow.
Film negatives usually also have much less contrast than the final images. This is compensated by the higher contrast reproduction by photographic paper or by increasing the contrast when scanning and post processing the scanned images.
Many photographic processes create negative images: the chemicals involved react when exposed to light, and during developing these exposed chemicals are retained and become opaque while the unexposed chemicals are washed away. However, when a negative image is created from a negative image (just like multiplying two negative numbers in mathematics) a positive image results (see Color print film, C-41 process). This makes most chemical based photography a two step process. These are called negative films and processes. Special films and development processes have been devised such that positive images can be created directly from film; these are called positive, or slide, or (perhaps confusingly) reversal film (see Transparency, Black and white reversal film, E-6 process).
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