Tuesday, September 18, 2012

Digital Color Spaces

Digital visualization software offers a variety of color environments to suit the needs of illustrators and designers. Each environment has its own purpose and uses. Most of us are quite familiar with the color spaces we use. Still, a basic understanding of all of the color options can be useful.

RGB (The Monitor Model)

The RGB color model is composed of the primary colors of red, green, and blue. The model, also known as the transmitted model, is an additive color system. Color systems are classified by how the primary colors relate to white. An additive system means that when all three primary colors are added they create white.  When two of the primary colors are combined they produce a secondary color. In the RGB system the secondary colors are cyan, magenta and yellow. Color monitors and digital projectors use the RGB system to display color. According to the trichromatic, Young-Helmholtz theory of color vision, the RGB color system aligns very closely to the way the human eye processes color.

RGB color model. © 2012 Don Arday.

CMYK (The Print Model)

CMYK stands for cyan, magenta, yellow, and black. Not to be confused with the “B” in RGB, black is represented by “K”. Also referred to as a reflective model, the CMYK system is a subtractive color system. When CMY are combined they create black. White is produced by the total lack of color and a white paper surface. When two of the primary colors are combined they produce a secondary color. In the CMYK system the secondary colors are red, green and blue. This alignment creates compatibility between the CMYK and RGB systems when creating work for print output on a monitor system.

CMYK color model. © 2012 Don Arday.

HSV (The Color Theory Model)

HSV is the acronym for hue, saturation and value. This color model is also called HSB or hue, saturation and brightness; and HSL or hue, saturation, and lightness. Very familiar to illustrators, the HSV model is based on standard artists color theory. Although not specifically relating to display hardware or printing equipment, it is an available color model in many image software programs as a more intuitive system for use by artists.

The “hue” is a color. For instance, the color of sky on a clear day is a blue hue. Every color is a hue.

The “saturation”, also called chroma, is a variation in intensity of a color. It is the amount of grey proportionate to the hue. Saturation can be used to alter a hue.

The “value” is the amount of lightness or darkness in a color. Brightness can also be used to alter a hue.

HSV color model. © 2012 Don Arday.

Lab (The Color Opposition Model)

Lab is an acronym. The “L” stands for lightness; the “a” signifies the range of opposition between green and magenta; and the “b” signifies the range of opposition between blue and yellow. Starting at a neutral center greens are negative values while magentas are positive values. Similarly, blues are negative values and yellows are positive values. This complimentary color concept should seem familiar to illustrators and designers. A simpler way to understand Lab color is to think of warm colors as positives and cool colors as negatives. The type of Lab color used in computing is the CIELab model. The CIE stands for the International Commission on Illumination. The Lab system is based on the Munsell color system. Basically, the Lab and Munsell color spaces are extruded 3D versions of the familiar “color wheel”. Although an excellent model for helping artists to understand color, the Lab system is not as compatible as RGB or HSV for use on monitors or in software programming due to its complexity. The next time you are working with an image in Photoshop, switch over to the Lab color space just to see how surprisingly different the colors in your image appear.

Lab color model. © 2012 Don Arday.

Grayscale (The Luminosity Model)

The Grayscale model is simply a range of tones between black and none or white. The range in the grayscale model used by Adobe contains 255 shades of gray plus white, and it is an 8-bit mode.

Grayscale color model. © 2012 Don Arday.

Indexed Color (The Color Compression Model)

Like the 8-bit Grayscale model, an Indexed Color model is limited to a finite index of colors. There are several Indexed Color models in common use, including a 16 Color model, the PhotoImpact Optimization Palette, the Graphics Interchange Format palette, and others. The Standard Web Browser Palette with its limit of 216 colors is an Indexed Color model. The Index color space in Adobe Photoshop is limited to 256 colors. In the case of the Photoshop Indexed Color space, colors in a non-indexed color image are altered to match the 256 colors available. To achieve this each pixel color is shifted to the nearest color in the color palette and then dithered with similar colors to optically mix the non-available colors.

ANPA (American Newspaper Publishers Association) index of color