Introduction
Color gamut defines a more specific range of colors from the range of colors identifiable by the human eye (i.e., the visible spectrum). While color imaging devices include a wide range of devices, such as digital cameras, scanners, monitors, and printers, since the range of colors they can reproduce varies, the color gamut is established to make these differences clear and to reconcile the colors that can be used in common between devices.
Types of Gamut
There are actually two types of color gamuts, Additive and Subtractive. Additive refers to the color that is generated by mixing together colored light to generate a final color. This is the style used by computers, televisions and other devices. It is more often referred to as RGB based on the red, green and blue light used to generate the colors.
Subtractive color is that used by mixing together dyes that prevent reflection of light that then produce a color. This is the style used for all printed media such as photos, magazines, and books. It is also generally referred to as CMYK based on the cyan, magenta, yellow and black pigments used in the printing.
Gamut Representation
Various methods are used to express the color gamut, common method used for display products is the xy chromaticity diagram of the XYZ color system established by the International Commission on Illumination (CIE). In an xy chromaticity diagram, the colors of the visible range are represented using numerical figures and graphed as color coordinates. In the following xy chromaticity diagram, the area shaped like an upside-down “U” surrounded by dotted lines indicates the range of colors visible to human beings with the naked eye.
Three standards frequently cited in relation to personal computers are sRGB, Adobe RGB, CIE976, and NTSC. The color gamut defined by each standard is depicted as a triangle on the xy chromaticity diagram. These triangles show the peak RGB coordinates connected by straight lines. A larger area inside a triangle is regarded to represent a standard capable of displaying more colors. For LCD monitors, this means that a product compatible with a color gamut associated with a larger triangle can reproduce a wider range of colors on screen.
Above image shows a CIE XYZ color system xy chromaticity diagram. The areas enclosed in dotted lines represent the range of colors human beings can see with the naked eye. The ranges corresponding to the sRGB, Adobe RGB, and NTSC standards defining color gamuts appear as triangles connecting their RGB peak coordinates. The color gamut of an LCD monitor’s hardware can be indicated using similar triangles. An LCD monitor is not capable of reproduction (display) of colors outside its color gamut.
So, to quantify the various color gamuts in terms of their relative range of color of narrowest to widest would be: CIE 1976 < sRGB < AdobeRGB < NTSC.
Monitors Gamut
Monitors are generally rated on their color by the percentage of colors out of a color gamut that are possible. Thus, a monitor that is rated at 100% NTSC can display all of the colors within the NTSC color gamut. A screen with a 50% NTSC color gamut can only represent half of those colors. The average computer monitor will display around 70 to 75% of the NTSC color gamut.
An LCD monitor’s backlight is the key factor in determining its overall color gamut. The most common backlight used in an LCD is a CCFL (Cold-Cathode Fluorescent Light). These can generally produce around the 75% NTSC color gamut. Improved CCFL lights can be used to generate roughly 100% NTSC. Newer LED backlighting has been able to actually generate greater than 100% NTSC color gamuts.