Monochrome
Monochrome comes from the Greek  (monochromos), meaning of one color, which is a combination of  (monos), meaning alone or solitary, and  (chroma), meaning color.  Monochromatic light is light of a single wavelength, though in practice it can refer to light of a narrow wavelength range.  A monochromatic object or image is one whose range of colors consists of shades of a single color or hue; monochrome images in neutral colors are also known as grayscale or black-and-white.

# Theory
In physics, the word is used more generally to refer to electromagnetic radiation of a single wavelength. In the physical sense, no real source of electromagnetic radiation is purely monochromatic, since that would require a wave of infinite duration as a consequence of the Fourier transform's localization property (cf. spectral coherence). Even sources such as lasers have some narrow range of wavelengths (known as the spectral linewidth) within which they operate.  In practice, filtered light, diffraction grating separated light and laser light are all routinely referred to as monochromatic.  Often light sources can be compared and one be labeled as more monochromatic (in a similar usage as monodispersity).  And a device which isolates light sources of a narrow bandwidth are called monochromators, even though the bandwidth is often explicitly specified, and thus a collection of wavelengths is understood.

# Application
For an image, the term monochrome is usually taken to mean the same as black-and-white or, more likely, grayscale, but may also be used to refer to other combinations containing only tones of a single color, such as green-and-white or green-and-black. It may also refer to sepia displaying tones from light tan to dark brown or cyanotype (blueprint) images, and early photographic methods such as Ambrotype, Tintype and Daguerreotype, each of which may be used to produce a monochromatic  image.
In computing, monochrome has two meanings:
- it may mean having only one color which is either on or off,
- allowing shades of that color, although the latter is more correctly known as grayscale.
A monochrome computer display is able to display only a single color, often green, amber, red or white, and often also shades of that color.
In film photography, monochrome is typically the use of black and white film.
Originally, all photography was done in monochrome until the invention of color film plates in the early 20th century.
In digital photography, monochrome is the capture of only shades of black by the sensor, or by post-processing a color image to present only the perceived brightness by combining the values of multiple channels (usually red, blue, and green). The weighting of individual channels may be selected to achieve a desired artistic effect - if only the red channel is selected by the weighting then the effect will be similar to that of using a red filter on panchromatic film. If the red channel is eliminated and the green and blue combined then the effect will be similar to that of Orthochromatic film or the use of a cyan filter on panchromatic film. The selection of weighting thus allows a wide range of artistic expression in the final monochromatic image.
For production of an anaglyph image the original color stereogram source may first be reduced to monochrome in order to simplify the rendering of the image. This is sometimes required in cases where a color image would render in a confusing manner given the colors and patterns present in the source image and the selection filters used (typically red and its complement cyan),