Understanding Color Models and Spot Color Systems

A color model is a system for creating a full range of colours from a small set of primary colors. There are two types of colour models: additive and subtractive. Additive color models use light to display color, while subtractive color models use printing inks. The most common color models that graphic designers work with are the CMYK model for printing and the RGB model for computer display. 

RGB Additive Color Model The RGB color model is an additive color model. In this case red, green and blue light are added together in various combinations to reproduce a wide spectrum of colors. The primary purpose of the RGB color model is for the display of images in electronic systems, such as on television screens and computer monitors and it’s also used in digital photography. Cathode ray tube, LCD, plasma and LED displays all utilize the RGB model. In order to create a color with RGB, three colored light beams (one red, one green, and one blue) must be superimposed. With no intensity,each of the three colors is perceived as black, while full intensity leads to a perception of seeing white. Differing intensities produce the hue of a color, while the difference between the most and least intense of the colors make the resulting color more or less saturated. Note the white centers that appear in the two color charts above. For web-page design the colors used are commonly specified using RGB. Today, with the predominance of 24-bit displays, it enables most users to see 16.7 million colors of HTML RGB code. In web page design, there are 216 so-called ‘web-safe’ RGB colors represented by hexadecimal values. Quite simply, the web-safe color palette consists of the 216 combinations of red, green and blue.

CMYK Subtractive Color Model The CMYK color model (four-color process) is a subtractive color model. Primarily used in printing, CMYK works by partially or completely masking colors on a white background. The printed ink reduces the light that would otherwise be reflected. That’s why this model is called subtractive because inks ‘subtract’ brightness from a white background from four colors: cyan, magenta, yellow and black. It is frequently suggested that the ‘K’ in CMYK comes from the last letter in ‘black’ and was chosen because B already refers to blue. However, this explanation is incorrect. 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. Black is used because the combination of the three primary colors (CMY) doesn’t produce a fully saturated black. This is evident in the central black color created by the overlapping circles in the color chart above. CMYK is able to produce the entire spectrum of visible colors due to the process of half-toning. In this process, each color is assigned a saturation level and miniscule dots of each of the three colors are printed in tiny patterns. This enables the human eye to perceive a specific color made from the combination. In order to improve print quality and reduce moiré patterns, the screen for each color is set at a different angle.

Additional Color Modes and Models

Bitmap

In the computer graphics environment, a bitmap or pixmap is a type of memory organization or image file format used to store digital images. The term bitmap simply means a ‘map of bits’. The term bitmap implies one bit per pixel, while pixmap is used for images with multiple bits per pixel. Many graphical user interfaces use bitmaps in their built-in graphics subsystems for example, the Microsoft Windows and OS/2 platforms. For designers, this mode is mostly used in graphic design to save high resolution line art images, like a scanned signature or logo when the vector equivalent no longer exists.

Duotone

Duotone is a halftone reproduction of an image using the superimposition of one contrasting color halftone (traditionally black) over another color halftone. This is most often used to bring out middle tones and highlights of an image. By comparison, a fake duotone is created by printing a single solid color with a contrasting halftone over it. This process can generally lose a lot of the contrast in the image, but it also creates a rich effect. Duotones, tritones and quadtones can be easily created using image manipulation programs. Sepia toning effect gives a black-and-white photograph a warmer tone and creates an archival look. It serves as a good example of how duotone techniques are used today. Previously, chemicals were used to create this distinct print effect.

Grayscale

In the worlds of both photography and computing, a grayscale digital image is an image in which the value of each pixel is a single sample, which means it carries only intensity information. Images of this type, also known as black-and-white, are composed exclusively of shades of gray, varying from black at the weakest intensity to white at the strongest. Grayscale images are also called monochromatic, denoting the presence of only one (mono) colour (chrome). Color images are built of stacked grayscale channels. For example, RGB images are composed of three independent channels for red, green and blue primary color components; CMYK images have four channels for cyan, magenta, yellow and black ink plates, etc.

Halftone

Halftone is the ‘industry standard’ reprographic technique. It simulates continuous tone imagery through the use of dots, varying either in size, in shape or in spacing. A ‘halftone’ is also used to refer specifically to the image that is produced by this process. This reproduction technique relies on creating a basic optical illusion—that these tiny halftone dots are blended into smooth tones by the human eye. Color printing is made possible by repeating the halftone process for each subtractive color—most commonly using what is called the ‘CMYK color model’. The resolution of a halftone screen is measured in lines per inch (lpi). This refers to the number of lines of dots in one inch. The higher the resolution being used, the greater the detail that can be reproduced.

HSV

HSV, which stands for hue, saturation and value, depicts three-dimensional color. HSV seeks to depict relationships between colors, and improve upon the RGB color model. If you think about HSV as a wheel, the center axis goes from white at the top to black at the bottom, with other neutral colors in between. The angle from the axis depicts the hue, the distance from the axis depicts saturation, and the distance along the axis depicts value.

HSL

HSL, like HSV, is a 3-D representation of color. HSL stands for hue, saturation, and lightness. The HSL color model has distinct advantages over the HSV model, in that the saturation and lightness components span the entire range of values.

Indexed color

Simply explained, the color of each pixel is represented by a number; each number (the index) corresponds to a color in the color table (the palette). In computing, indexed colour is a technique used to manage digital image colours in a limited fashion, in order to save computer memory and file storage, while speeding up display refresh and file transfers. A graphic designer will usually encounter indexed color for web design or in multimedia applications.

LAB

LAB is designed to approximate human vision. Unlike RGB and CMYK, LAB is not device-dependent. In this three-dimensional model, the ‘L’ stands for the lightness of the color, with 0 producing black and 100 producing a diffused white. The ‘A’ is the redness vs. greenness, while the ‘B’ is the yellowness vs. blueness.

NCS

The Natural Color System (NCS) is a color opponency system based on six colors that cannot be used to describe one another: white, black, red, yellow, green and blue. Unlike the additive RGB system or the subtractive CMYK system, which are based on reactions of the eye’s color-receptive cones, NCS colors are processed in the retina’s ganglion cells.

Spot Color Systems Classification

Pantone Matching System (PMS)

Pantone Inc. is, by far, the world-renowned authority on color. It is best known for its Pantone Matching System (PMS) used in a variety of industries, but primarily in offset printing. The PANTONE® name is known worldwide as the standard language for color communication, from designer to manufacturer to retailer to customer. Most applications that support color printing allow you to specify colors by indicating the Pantone name or number. This assures that you get the right color when the file is printed, even though the color may not look right when displayed on your monitor.

ANPA

The American Newspaper Publishers Association (ANPA) has a palette of 300 spot colors for spot color usage in newspapers.

DIC

The DIC Colour Guide and TOYO are the common spot color matching systems used in Japan.

FOCOLTONE

A color matching system used to specify and match process colors. The FOCOLTONE Color Chart shows samples of 763 four-color combinations of the process colors.

Hexachrome

Hexachrome was a six-color printing process designed by Pantone Inc. In addition to custom CMYK inks, Hexachrome added orange and green inks for better color reproduction. Discontinued by Pantone in 2008 when Adobe Systems stopped supporting their software.

HKS

HKS is a color system which contains 120 spot colours and 3250 tones for both coated and uncoated paper. HKS is an abbreviation of three German printer’s ink manufacturers.

Munsell

The Munsell color system is a color space that specifies colors based on three color dimensions: hue, value (lightness) and chroma (colour purity). The Munsell system organizes color the way the human eye sees color. It is mostly used in manufacturing.

TOYO

The TOYO and DIC Color Guide are the common spot color matching systems used in Japan.

TRUEMATCH

An electronic equivalent to the Munsel and Pantone systems that is useful for accurate video color displays.