CMYK
The CMYK color model (process color, four color) is a subtractive color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key (black). Though it varies by print house, press operator, press manufacturer, and press run, ink is typically applied in the order of the abbreviation.
The "K" in CMYK stands for key since in four-color printing cyan, magenta, and yellow printing plates are carefully keyed or aligned with the key of the black key plate. Some sources suggest that the "K" in CMYK comes from the last letter in "black" and was chosen because B already means blue. However, this explanation, although useful as a mnemonic, is incorrect.
The CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected. Such a model is called subtractive because inks "subtract" brightness from white.
In additive color models such as RGB, white is the "additive" combination of all primary colored lights, while black is the absence of light. In the CMYK model, it is the opposite: white is the natural color of the paper or other background, while black results from a full combination of colored inks. To save money on ink, and to produce deeper black tones, unsaturated and dark colors are produced by using black ink instead of the combination of cyan, magenta and yellow.
http://en.wikipedia.org/wiki/CMYK_color_model
RGB
The RGB color model is an additive color model in which red, green, and blue light are added together in various ways to reproduce a broad array of colours. The name of the model comes from the initials of the three additive primary colours, red, green, and blue.
The main purpose of the RGB color model is for the sensing, representation, and display of images in electronic systems, such as televisions and computers, though it has also been used in conventional photography. Before the electronic age, the RGB color model already had a solid theory behind it, based in human perception of colours.
RGB is a device-dependent color model: different devices detect or reproduce a given RGB value differently, since the color elements (such as phosphors or dyes) and their response to the individual R, G, and B levels vary from manufacturer to manufacturer, or even in the same device over time. Thus an RGB value does not define the same color across devices without some kind of color management.
Typical RGB input devices are color TV and video cameras, image scanners, and digital cameras. Typical RGB output devices are TV sets of various technologies (CRT, LCD, plasma, etc.), computer and mobile phone displays, video projectors, multicolor LED displays, and large screens such as JumboTron, etc. Color printers, on the other hand, are not RGB devices, but subtractive color devices (typically CMYK color model).
This article discusses concepts common to all the different color spaces that use the RGB color model, which are used in one implementation or another in color image-producing technology.
http://en.wikipedia.org/wiki/RGB_color_model
Hexachrome
Hexachrome was a six-color printing process designed by Pantone Inc. In addition to custom CMYK inks, Hexachrome added orange and green inks to expand the color gamut, for better color reproduction. It was therefore also known as a CMYKOG process. Hexachrome was discontinued by Pantone in 2008 when Adobe Systems stopped supporting their HexWare plugin software. While the details of Hexachrome were not secret, use of Hexachrome was limited by trademark and patent to those obtaining a license from Pantone. The inventor of Hexachrome was Richard Herbert, who is also the president of Pantone Inc.
http://en.wikipedia.org/wiki/Hexachrome
Spot Colour
In offset printing, a spot color is any color generated by an ink (pure or mixed) that is printed using a single run.
The widely spread offset-printing process is composed of four spot colors: Cyan, Magenta, Yellow, and Key (black) commonly referred to as CMYK. More advanced processes involve the use of six spot colors (hexachromatic process), which add Orange and Green to the process (termed CMYKOG). The two additional spot colors are added to compensate for the ineffective reproduction of faint tints using CMYK colors only. However, offset technicians around the world use the term spot color to mean any color generated by a non-standard offset ink; such as metallic, fluorescent, spot varnish, or custom hand-mixed inks.
When making a multi-color print with a spot color process, every spot color needs its own lithographic film. All the areas of the same spot color are printed using the same film, hence, using the same lithographic plate. The dot gain, hence the screen angle and line frequency, of a spot color vary according to its intended purpose. Spot lamination and UV coatings are sometimes referred to as 'spot colors', as they share the characteristics of requiring a separate lithographic film and print run.
http://en.wikipedia.org/wiki/Spot_color
The Pantone Color Matching System
The Pantone Color Matching System is largely a standardized color reproduction system. By standardizing the colors, different manufacturers in different locations can all refer to the Pantone system to make sure colors match without direct contact with one another.
One such use is standardizing colors in the CMYK process. The CMYK process is a method of printing color by using four inks — cyan, magenta, yellow, and black. A majority of the world's printed material is produced using the CMYK process, and there is a special subset of Pantone colors that can be reproduced using CMYK. Those that are possible to simulate through the CMYK process are labeled as such within the company's guides.
However, most of the Pantone system's 1,114 spot colours cannot be simulated with CMYK but with 13 base pigments (15 including white and black) mixed in specified amounts.
The Pantone system also allows for many special colors to be produced, such as metallics and fluorescents. While most of the Pantone system colors are beyond the printed CMYK gamut, it was only in 2001 that Pantone began providing translations of their existing system with screen-based colors. (Screen-based colors use the RGB color model — red, green, blue — system to create various colours.) The Goe system has RGB and LAB values with each color.
Pantone colours are described by their allocated number (typically referred to as, for example, "PMS 130"). PMS colors are almost always used in branding and have even found their way into government legislation and military standards (to describe the colors of flags and seals). In January 2003, the Scottish Parliament debated a petition to refer to the blue in the Scottish flag (saltire) as "Pantone 300". Countries such as Canada and South Korea and organizations such as the FIA have also chosen to refer to specific Pantone colors to use when producing flags. U.S. states including Texas have set legislated PMS colors of their flags. It has also been used in an art project by the Brazilian photographer Angelica Dass. which applies Pantone to the human skin color spectrum.
http://en.wikipedia.org/wiki/Pantone
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