A "false color" image showing the Chesapeake Bay and the city of Baltimore. The Chesapeake Bay is the largest Estuary in the United States.

This "true color" image shows the same region as the "false color" image above, but uses true colors, e. g. , the plants are shown in green.

A false-color image is an image that depicts a subject in colors that differ from those a faithful full-color photograph would show.

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 chemistries of the display media and an eye.

In a false-color image this close correspondence between subject color and image color is violated. That can happen in many ways. For example, a photographic negative could be called a false-color image, since it shows the complementary colors of its subject. In photography a negative may refer to three different things although they are all related However, the term "false-color" is typically used to describe images whose colors represent measured intensities outside the visible portion of the electromagnetic spectrum (or outside the electromagnetic spectrum altogether). The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies

For example infrared film captures a small region of the near infrared spectrum (wavelengths from about 700 nm to 900 nm). Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Black-and-white infrared film maps the average intensity in this portion of the spectrum to a "false" gray value. Typical color infrared film is sensitive in the visible and near infrared range; it is usually used, in conjunction with a blue-cut filter, for shifting the near infrared spectrum into the visible spectrum (ca. 400 nm to 700 nm). Loosely speaking, this process effectively subtracts ca. 150 nm from the subject wavelength: a green subject is depicted as blue; a red subject is depicted as green; and an infrared subject is depicted as red (blue subjects cannot be depicted; they appear black).

More generally, false-color images can be generated by digital image processing techniques to represent up to three independent measurements over a two-dimensional map or image. Digital image processing is the use of computer Algorithms to perform Image processing on Digital images As a subfield of Digital signal processing For example, a satellite might capture average intensities in short ranges of the ultraviolet spectrum and the near infrared spectrum. This article is about artificial satellites For natural satellites also known as moons see Natural satellite. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays These measurements can be combined with altitude information in such a way that blue represents ultraviolet, green represents altitude, and red represents infrared. Then a bright yellow pixel indicates a high-altitude object that emits or reflects infrared light but not ultraviolet light; a magenta pixel indicates a low-altitude object that emits or reflects both infrared and ultraviolet light; etc. Because 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. In Psychology, visual perception is the ability to interpret information from Visible light reaching the Eyes The resulting Perception is also

A pseudo-color image is derived from a greyscale image by mapping each pixel value to a color according to a table or function. In Computing, a grayscale or greyscale Digital image is an image in which the value of each Pixel In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image 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. Altitude is the Elevation of a point or object from a known level or datum (plural data 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 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 Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface Although pseudo-coloring does not increase the information contents of the original image, it can make some details more visible, by increasing the distance in color space between successive gray levels. 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 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 satellites, the Hubble Space Telescope, and the Cassini-Huygens space probe's images of the rings of Saturn. This article is about artificial satellites For natural satellites also known as moons see Natural satellite. A weather satellite is a type of Satellite that is primarily used to monitor the Weather and Climate of the Earth. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into Cassini–Huygens is a joint NASA / ESA / ASI Robotic spacecraft mission currently studying the planet Saturn and its A space probe is a scientific Space exploration mission in which a Robotic spacecraft leaves the Gravity well of Earth and approaches the Infrared cameras used for thermal imaging often show their image in false colors. A thermographic camera, sometimes called a FLIR (Forward Looking InfraRed or an infrared camera less specifically is a device that forms an image using Infrared wiki stranglesnakejpg|thumb|Thermographic image of a Snake held by a human]] Infrared Thermography, thermal imaging, or thermal video, is a type of

See also

• A false-color satellite image of Las Vegas
• NASA World Wind uses several false-color satellite image layers
• Density slicing
• List of software palettes - False color palettes section

External links

• Why do satellite images look so different?
• UCSC
• NASA
• Harvard
• Kodak Tech Pub TI2323