![MSU-MR-Meteor-M2-2](https://upload.wikimedia.org/wikipedia/commons/c/cf/MSU-MR-Meteor-M2-2.png)
False color (or pseudo color) refers to a group of
color
Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
rendering methods used to display images in color which were recorded in the
visible
Visibility, in meteorology, is a measure of the distance at which an object or light can be seen.
Visibility may also refer to:
* A measure of turbidity in water quality control
* Interferometric visibility, which quantifies interference contrast ...
or non-visible parts of the
electromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from ...
. A false-color image is an image that depicts an object in
color
Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
s that differ from those a
photograph
A photograph (also known as a photo, image, or picture) is an image created by light falling on a photosensitive surface, usually photographic film or an electronic image sensor, such as a CCD or a CMOS chip. Most photographs are now create ...
(a true-color image) would show. In this image, colors have been assigned to three different
wavelengths
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
that our eyes cannot normally see.
In addition, variants of ''false color'' such as pseudocolor, density slicing, and choropleths are used for
information visualization
Information is an abstract concept that refers to that which has the power to inform. At the most fundamental level information pertains to the interpretation of that which may be sensed. Any natural process that is not completely random, ...
of either data gathered by a single grayscale channel or data not depicting parts of the electromagnetic spectrum (e.g. elevation in relief maps or tissue types in
magnetic resonance imaging
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...
).
Types of color renderings
True color
The concept behind true color can help in understanding false color. An image is called a ''true-color'' image when it offers a natural
color
Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
rendition, or when it comes close to it. This means that the colors of an object in an image
appear to a human observer the same way as if this same observer were to directly view the object: A green tree appears green in the image, a red apple red, a blue sky blue, and so on.
When applied to black-and-white images, ''true-color'' means that the perceived lightness of a subject is preserved in its depiction.
![Burns cliff](https://upload.wikimedia.org/wikipedia/commons/a/a4/Burns_cliff.jpg)
Absolute true-color rendering is impossible.
There are three major sources of color error (
metameric
In biology, metamerism is the phenomenon of having a linear series of body segments fundamentally similar in structure, though not all such structures are entirely alike in any single life form because some of them perform special functions.
In ...
failure):
* Different
spectral sensitivities of the human eye and of an image capture device (e.g. a
camera
A camera is an Optics, optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), ...
).
* Different spectral emissions / reflections of the object and of the image render process (e.g. a
printer
Printer may refer to:
Technology
* Printer (publishing), a person or a company
* Printer (computing), a hardware device
* Optical printer for motion picture films
People
* Nariman Printer (fl. c. 1940), Indian journalist and activist
* James ...
or
monitor
Monitor or monitor may refer to:
Places
* Monitor, Alberta
* Monitor, Indiana, town in the United States
* Monitor, Kentucky
* Monitor, Oregon, unincorporated community in the United States
* Monitor, Washington
* Monitor, Logan County, West ...
).
* Differences in spectral irradiance in the case of reflective images (e.g. photo prints) or reflective objects – see
color rendering index
A color rendering index (CRI) is a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with a natural or standard light source. Light sources with a high CRI are desirable in ...
(CRI) for details.
The result of a metameric failure would be for example an image of a green tree which shows a different shade of green than the tree itself, a different shade of red for a red apple, a different shade of blue for the blue sky, and so on.
Color management
In digital imaging systems, color management (or colour management) is the controlled conversion between the color representations of various devices, such as image scanners, digital cameras, monitors, TV screens, film printers, computer printer ...
(e.g. with
ICC profile
In color management, an ICC profile is a set of data that characterizes a color input or output device, or a color space, according to standards promulgated by the International Color Consortium (ICC). Profiles describe the color attributes of a ...
s) can be used to mitigate this problem within the physical constraints.
Approximate true-color images gathered by spacecraft are an example where images have a certain amount of metameric failure, as the spectral bands of a spacecraft's camera are chosen to gather information on the physical properties of the object under investigation, and are not chosen to capture true-color images.
False color
In contrast to a true-color image, a false-color image sacrifices natural color rendition in order to ease the
detection of features that are not readily discernible otherwise – for example the use of near infrared for the detection of vegetation in satellite images.
While a false-color image can be created using solely the visual spectrum (e.g. to accentuate color differences), typically some or all data used is from
electromagnetic radiation
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, inf ...
(EM) outside the
visual spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' or simply light. A typical human eye will respond to wavele ...
(e.g.
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
,
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
or
X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
). The choice of spectral bands is governed by the physical properties of the object under investigation.
As the human eye uses three spectral bands (see
trichromacy
Trichromacy or trichromatism is the possessing of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats.
The normal expla ...
for details), three spectral bands are commonly combined into a false-color image. At least two spectral bands are needed for a false-color encoding,
and it is possible to combine more bands into the three visual RGB bands – with the eye's ability to discern three channels being the limiting factor. In contrast, a "color" image made from one spectral band, or an image made from data consisting of non-EM data (e.g. elevation, temperature, tissue type) is a pseudocolor image (see below).
For true color, the
RGB
The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three addi ...
channels (red "R", green "G" and blue "B") from the camera are mapped to the corresponding RGB channels of the image, yielding a "RGB→RGB" mapping. For false color this relationship is changed. The simplest false-color encoding is to take an RGB image in the visible spectrum, but map it differently, e.g. "GBR→RGB". For traditional false-color satellite images of
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
a "NRG→RGB" mapping is used, with "N" being the near-infrared spectral band (and the blue spectral band being unused) – this yields the typical "vegetation in red" false-color images.
False color is used (among others) for satellite and space images: Examples are
remote sensing
Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Earth ...
satellites (e.g.
Landsat
The Landsat program is the longest-running enterprise for acquisition of satellite imagery of Earth. It is a joint NASA / USGS program. On 23 July 1972, the Earth Resources Technology Satellite was launched. This was eventually renamed to Lan ...
, see example above),
space telescope
A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first operational telescopes were the American Orbiting Astronomical Observatory, OAO-2 launched ...
s (e.g. the
Hubble Space Telescope
The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
) or
space probe
A space probe is an artificial satellite that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; or ent ...
s (e.g. ''
Cassini-Huygens''). Some spacecraft, with
rovers (e.g. the
Mars Science Laboratory
Mars Science Laboratory (MSL) is a robotic spacecraft, robotic space probe mission to Mars launched by NASA on November 26, 2011, which successfully landed ''Curiosity (rover), Curiosity'', a Mars rover, in Gale (crater), Gale Crater on August ...
''Curiosity'') being the most prominent examples, have the ability to capture approximate true-color images as well.
Weather satellite
A weather satellite or meteorological satellite is a type of Earth observation satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be polar orbiting (covering the entire Earth asynchronously), or ge ...
s produce, in contrast to the spacecraft mentioned previously, grayscale images from the visible or infrared spectrum.
False color has a range of scientific applications. Spacecraft often employ false-color methods to help understand the composition of structures in the universe such as nebula and galaxies. The frequency of light emitted by different ions in space are assigned contrasting colors, allowing the chemical composition of complex structures to be better separated and visualised. The image of the Eagle Nebula above is a typical example of this; the Hydrogen and Oxygen ions have been assigned green and blue respectively. The large amounts of green and blue in the image show that there is a large amount of Hydrogen and Oxygen in the nebula.
On 26 October 2004, the NASA/ESA Cassini-Huygens spacecraft captured a false-color image of Titan, Saturn's largest moon. The image was captured in Ultraviolet and Infrared wavelengths, both invisible to the human eye. In order to provide a visual representation, false color techniques were used. The infrared data was mapped to red and green colors, and ultraviolet mapped to blue.
Pseudocolor
A pseudocolor image (sometimes styled pseudo-color or pseudo color) is derived from a
grayscale image
In digital photography, computer-generated imagery, and colorimetry, a grayscale image is one in which the value of each pixel is a single sample representing only an ''amount'' of light; that is, it carries only intensity information. Gray ...
by mapping each
intensity value to a color according to a table or function. Pseudo color is typically used when a single channel of data is available (e.g. temperature, elevation, soil composition, tissue type, and so on), in contrast to false color which is commonly used to display three channels of data.
Pseudocoloring can make some details more visible, as the
perceived difference in
color space
A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of colorwhether such representation entails an analog or a digital represent ...
is bigger than between successive gray levels alone. On the other hand, the color mapping function should be chosen to make sure the
lightness
Lightness is a visual perception of the luminance (L) of an object. It is often judged relative to a similarly lit object. In colorimetry and color appearance models, lightness is a prediction of how an illuminated color will appear to a stan ...
of the color is still monotonic, or the uneven change would make it hard to interpret levels, for both normal and colorblind viewers. One offender is the commonly-used "rainbow" palette, with a back-and-forth change in lightness. (See also .)
A typical example for the use of pseudo color is
thermography
Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a Thermographic camera, thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are ...
(thermal imaging), where
infrared camera
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
s feature only one spectral band and show their grayscale images in pseudo color.
Another familiar example of pseudo color is the encoding of
elevation
The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § Vert ...
using
hypsometric tints
Hypsometric tints (also called layer tinting, elevation tinting, elevation coloring, or hysometric coloring) are colors placed between contour lines to indicate elevation. These tints are shown as bands of color in a graduated scheme or as a co ...
in physical
relief maps, where negative values (below
sea level
Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...
) are usually represented by shades of blue, and positive values by greens and browns.
Depending on the table or function used and the choice of data sources, pseudocoloring may increase the information contents of the original image, for example adding geographic information, combining information obtained from infrared or ultra-violet light, or other sources like
MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...
scans.
A further application of pseudocoloring is to store the results of image elaboration; that is, changing the colors in order to ease understanding an image.
Density slicing
![Tasmania 27nov81](https://upload.wikimedia.org/wikipedia/commons/1/15/Tasmania_27nov81.png)
Density slicing, a variation of pseudo color, divides an image into a few colored bands and is (among others) used in the analysis of
remote sensing
Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Earth ...
images. For density slicing the range of grayscale levels is divided into intervals, with each interval assigned to one of a few discrete colors – this is in contrast to pseudo color, which uses a continuous color scale. For example, in a grayscale
thermal image the temperature values in the image can be split into bands of 2 °C, and each band represented by one color – as a result the temperature of one spot in the thermograph can be easier acquired by the user, because the discernible differences between the discrete colors are greater than those of images with continuous grayscale or continuous pseudo color.
Choropleth
A choropleth is an
image
An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...
or
map
A map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes.
Many maps are static, fixed to paper or some other durable medium, while others are dynamic or interactive. Although ...
in which areas are colored or patterned proportionally to the
category
Category, plural categories, may refer to:
Philosophy and general uses
* Categorization, categories in cognitive science, information science and generally
*Category of being
* ''Categories'' (Aristotle)
*Category (Kant)
*Categories (Peirce)
* ...
or
value
Value or values may refer to:
Ethics and social
* Value (ethics) wherein said concept may be construed as treating actions themselves as abstract objects, associating value to them
** Values (Western philosophy) expands the notion of value beyo ...
of one or more
variables being represented. The variables are mapped to a few colors; each area contributes one data point and receives one color from these selected colors. Basically it is density slicing applied to a pseudocolor overlay. A choropleth map of a
geographic
Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and ...
area is thus an extreme form of false color.
False color in the arts
While artistic rendition lends to subjective expression of color,
Andy Warhol
Andy Warhol (; born Andrew Warhola Jr.; August 6, 1928 – February 22, 1987) was an American visual artist, film director, and producer who was a leading figure in the visual art movement known as pop art. His works explore the relationsh ...
(1928–1987) has become a culturally significant figure of the
modern art
Modern art includes artistic work produced during the period extending roughly from the 1860s to the 1970s, and denotes the styles and philosophies of the art produced during that era. The term is usually associated with art in which the tradi ...
movement by creating false-color paintings with
screen printing
Screen printing is a printing technique where a mesh is used to transfer ink (or dye) onto a substrate, except in areas made impermeable to the ink by a blocking stencil. A blade or squeegee is moved across the screen to fill the open mes ...
techniques. Some of Warhol's most recognizable prints include a replication of
Marilyn Monroe
Marilyn Monroe (; born Norma Jeane Mortenson; 1 June 1926 4 August 1962) was an American actress. Famous for playing comedic " blonde bombshell" characters, she became one of the most popular sex symbols of the 1950s and early 1960s, as wel ...
, her image based on a
film frame
In filmmaking, video production, animation, and related fields, a frame is one of the many ''still images'' which compose the complete ''moving picture''. The term is derived from the historical development of film stock, in which the sequentia ...
from the movie ''
Niagara''. The subject was a
sex symbol
A sex symbol or icon is a person or character widely considered sexually attractive.Pam Cook, "The trouble with sex: Diana Dors and the Blonde bombshell phenomenon", In: Bruce Babinigton (ed.), ''British Stars and Stardom: From Alma Taylor to ...
and
film noir
Film noir (; ) is a cinematic term used primarily to describe stylish Hollywood crime dramas, particularly those that emphasize cynical attitudes and motivations. The 1940s and 1950s are generally regarded as the "classic period" of American ' ...
starlet whose death in 1962 influenced the artist. A series of prints were made with endearment but expose her persona as an illusion through his
assembly line
An assembly line is a manufacturing process (often called a ''progressive assembly'') in which parts (usually interchangeable parts) are added as the semi-finished assembly moves from workstation to workstation where the parts are added in seq ...
style of art production which are non-erotic and slightly grotesque. Using various ink color palettes, Warhol immersed himself in a process of repetition that serves to compare personas and everyday objects to the qualities of
mass production
Mass production, also known as flow production or continuous production, is the production of substantial amounts of standardized products in a constant flow, including and especially on assembly lines. Together with job production and batch ...
and
consumerism
Consumerism is a social and economic order that encourages the acquisition of goods and services in ever-increasing amounts. With the Industrial Revolution, but particularly in the 20th century, mass production led to overproduction—the supp ...
. The colors of ink were selected through experimentation of
aesthetics
Aesthetics, or esthetics, is a branch of philosophy that deals with the nature of beauty and taste, as well as the philosophy of art (its own area of philosophy that comes out of aesthetics). It examines aesthetic values, often expressed thr ...
and do not correlate to false-color rendering of the
electromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from ...
employed in
remote sensing
Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Earth ...
image processing. For years the artist continued
screen printing
Screen printing is a printing technique where a mesh is used to transfer ink (or dye) onto a substrate, except in areas made impermeable to the ink by a blocking stencil. A blade or squeegee is moved across the screen to fill the open mes ...
false-color images of Marilyn Monroe, perhaps his most referenced work being ''
Turquoise Marilyn'' which was bought in May 2007 by a private collector for 80 million US dollars.
See also
*
Color coding in data visualization
Data visualization achieves its significance today due to information technology: big data processed in computers with capable visualization software, combined with statistical techniques and color coding on electronic displays. This article is ...
*
NASA World Wind
NASA WorldWind is an open-source (released under the NOSA license and the Apache 2.0 license) virtual globe. According to the website (https://worldwind.arc.nasa.gov/), "WorldWind is an open source virtual globe API. WorldWind allow ...
uses several false-color satellite image layers
*
*
Imaginary colors
Impossible colors are colors that do not appear in ordinary visual functioning. Different color theories suggest different hypothetical colors that humans are incapable of perceiving for one reason or another, and fictional colors are rou ...
, points in a color space that correspond to a color perception that cannot be produced by any physical (non-negative) light spectrum.
*
Spectral imaging
Spectral imaging is imaging that uses multiple bands across the electromagnetic spectrum. While an ordinary camera captures light across three wavelength bands in the visible spectrum, red, green, and blue (RGB), spectral imaging encompasses ...
, collects and processes information from across the electromagnetic spectrum.
References
External links
NASA: Landsat
{{DEFAULTSORT:False-Color
Photographic techniques
Color
Visualization (graphics)
Scientific visualization