False-color
Encyclopedia
A false-color image is an image that depicts a subject in color
s that differ from those a full-color photograph would show.
In a false-color se human visual perception
is limited to three independent coordinates (Combination of Red, Green and Blue) at most three measurements can be depicted in such a way.
value to a color according to a table or function. A familiar example is the encoding of altitude
using hypsometric tints
in physical relief maps
, where negative values (below sea level
) are usually represented by shades of blue, and positive values by greens and browns. Pseudo-coloring can make some details more visible, by increasing the distance in color space
between successive gray levels. Pseudo-coloring can be used to store the results of image elaboration; that is, changing the colors in order to ease understanding the image. Alternatively, depending on the table or function used, pseudo-coloring may increase the information contents of the original image, for example adding geographic information, combining information obtained from infra-red or ultra-violet light, or MRI
scans.
Pseudo-color images differ from false-color images in that they are made from only one original gray-scale image, rather than two or three.
False-color and pseudo-color images are frequently used for viewing satellite images, such as from weather satellite
s, the Hubble Space Telescope
, and the Cassini-Huygens
space probe
's images of the rings of Saturn
. Infrared cameras used for thermal imaging often show their image in false colors. In the notes for a toolkit called GIPSY that might be used for this application area (written in 2001) it is said:
The used term PseudoColor refers to a pixel encoding category for X11 systems that represents pseudo color. This category is still present in the current implementation provided by Xorg. Even if hardware based 8 bit palletized modes might be a rather common bitness variant for the semiconductor based implementation (the most prominent ancestor is the IBM VGA graphics adapter) of pseudo-color modes still the principle is not at all limited to that depth. E.g. announcements for medical devices from 1999 report RAMDAC designs with 10 bit being fed with image data of 12 bit width using a 12-to-10-bit conversion table plus several other modes.
or map
in which areas are colored or patterned proportionally to the category
or value
of one or more variables
being represented, with little regard for details of the form of the underlying object. A choropleth map of a geographic area is thus an extreme form of false-color.
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
s that differ from those a full-color photograph would show.
True- and false-color
A true-color image of a subject is an image that appears to the human eye just like the original subject would: a green tree appears green in the image, a red apple red, a blue sky blue, etc. When applied to black-and-white images, true-color means that the perceived lightness of a subject is preserved in its depiction. Absolute true-color is impossible to achieve due to the differences between the chemistry of the display medium and the materials in the original scene.In a false-color se human visual perception
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
is limited to three independent coordinates (Combination of Red, Green and Blue) at most three measurements can be depicted in such a way.
Pseudo-color
A pseudo-color image is derived from a greyscale image by mapping each pixelPixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
value to a color according to a table or function. A familiar example is the encoding of altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
using hypsometric tints
Hypsometric tints
Hypsometric tints are related to contour lines. They can be used to depict ranges of elevation as bands of color, usually in a graduated scheme, or as a color ramp applied to contour lines themselves. A typical scheme progresses from dark greens for lower elevations up through yellows/browns, and...
in physical relief maps
Cartographic relief depiction
Terrain or relief is an essential aspect of physical geography, and as such its portrayal presents a central problem in cartography, and more recently GIS and 3D Visualization....
, where negative values (below sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
) are usually represented by shades of blue, and positive values by greens and browns. Pseudo-coloring can make some details more visible, by increasing the distance in color space
Color space
A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components...
between successive gray levels. Pseudo-coloring can be used to store the results of image elaboration; that is, changing the colors in order to ease understanding the image. Alternatively, depending on the table or function used, pseudo-coloring may increase the information contents of the original image, for example adding geographic information, combining information obtained from infra-red or ultra-violet light, or MRI
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
scans.
Pseudo-color images differ from false-color images in that they are made from only one original gray-scale image, rather than two or three.
False-color and pseudo-color images are frequently used for viewing satellite images, such as from weather satellite
Weather satellite
The weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be either polar orbiting, seeing the same swath of the Earth every 12 hours, or geostationary, hovering over the same spot on Earth by orbiting over the equator while...
s, the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
, and the Cassini-Huygens
Cassini-Huygens
Cassini–Huygens is a joint NASA/ESA/ASI spacecraft mission studying the planet Saturn and its many natural satellites since 2004. Launched in 1997 after nearly two decades of gestation, it includes a Saturn orbiter and an atmospheric probe/lander for the moon Titan, although it has also returned...
space probe
Space probe
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...
's images of the rings of Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
. Infrared cameras used for thermal imaging often show their image in false colors. In the notes for a toolkit called GIPSY that might be used for this application area (written in 2001) it is said:
- The TrueColor visual lacks the capability of PseudoColor to modify the color representation of images after they have been put onto the display. In GIPSY this capability is used to offer the user a fast and convenient way to change contrast, brightness and colors of displayed images. In TrueColor this is not easily possible. There the image needs to be recalculated and reloaded.
The used term PseudoColor refers to a pixel encoding category for X11 systems that represents pseudo color. This category is still present in the current implementation provided by Xorg. Even if hardware based 8 bit palletized modes might be a rather common bitness variant for the semiconductor based implementation (the most prominent ancestor is the IBM VGA graphics adapter) of pseudo-color modes still the principle is not at all limited to that depth. E.g. announcements for medical devices from 1999 report RAMDAC designs with 10 bit being fed with image data of 12 bit width using a 12-to-10-bit conversion table plus several other modes.
Choropleth
A choropleth is an imageImage
An image is an artifact, for example a two-dimensional picture, that has a similar appearance to some subject—usually a physical object or a person.-Characteristics:...
or map
Map
A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes....
in which areas are colored or patterned proportionally to the category
Category (mathematics)
In mathematics, a category is an algebraic structure that comprises "objects" that are linked by "arrows". A category has two basic properties: the ability to compose the arrows associatively and the existence of an identity arrow for each object. A simple example is the category of sets, whose...
or value
Value (mathematics)
In mathematics, value commonly refers to the 'output' of a function. In the most basic case, that of unary, single-valued functions, there is one input and one output .The function f of the example is real-valued, since each and every possible function value is real...
of one or more variables
Variable (mathematics)
In mathematics, a variable is a value that may change within the scope of a given problem or set of operations. In contrast, a constant is a value that remains unchanged, though often unknown or undetermined. The concepts of constants and variables are fundamental to many areas of mathematics and...
being represented, with little regard for details of the form of the underlying object. A choropleth map of a geographic area is thus an extreme form of false-color.
See also
- A false-color satellite image of Las Vegas
- NASA World WindNASA World WindWorld Wind is an open-source virtual globe developed by NASA and the open source community for use on personal computers. Old versions need Microsoft Windows but the more recent Java version, , is cross platform and provides a suite of . The World Wind Java version was awarded in November 2009...
uses several false-color satellite image layers - Density slicingDensity slicingDensity slicing is a digital data interpretation method used in analysis of remotely sensed imagery to enhance the information gathered from an individual brightness band. Density slicing is done by dividing the range of brightnesses in a single band into intervals, then assigning each interval to...
- List of software palettes - False color palettes section