- The inch (abbreviation: in or ″) is a unit of length in the (British) imperial and United States customary systems of measurement now formally equal to ?1/36 yard but usually understood as ?1/12 of a foot. Derived from the Roman uncia ("twelfth"), inch is also sometimes used to translate related units in other measurement systems, usually understood as deriving from the width of the human thumb. Traditional standards for the exact length of an inch have varied in the past, but since the adoption of the international yard during the 1950s and 1960s it has been based on the metric system and defined as exactly 2.54 cm..
In digital imaging, a pixel, pel,dots, or picture element is a physical point in a raster image, or the smallest addressable element in an all points addressable display device; so it is the smallest controllable element of a picture represented on the screen.
Each pixel is a sample of an original image; more samples typically provide more accurate representations of the original. The intensity of each pixel is variable. In color imaging systems, a color is typically represented by three or four component intensities such as red, green, and blue, or cyan, magenta, yellow, and black.