Additive color mixing: adding red to green will yield yellow; adding yellow to blue will yield white.
The RGB color model is an additive color model in which red, green, and bluelight are combined in various ways to create other colors. The very idea for the model itself and the abbreviation "RGB" come from the three primary colors in additive light models.
Although the peak responsitivities of the cones do not occur at the red, green and blue wavelengths, those three colors are described as primary because they can be used relatively independently to stimulate the three kinds of cones.
To generate optimal color ranges for species other than humans, other primary colors would have to be used. For species with four different color receptors, such as many birds, one would use four primary colors; for species with just two kinds of receptors, such as most mammals, one would use two primaries.
One common application of the RGB color model is the display of colors on a cathode ray tube or liquid crystal display such as a television picture tube or a computer's monitor. Each pixel on the screen can be represented in the computer's memory as independent values for red, green and blue. These values are converted into intensities and sent to the cathode ray tube or LCD display. By using the appropriate combination of red, green and blue light intensities, the screen can reproduce many of the colors between its black level and white point. Typical display hardware used for computer monitors in 2003 uses a total of 24 bits of information for each pixel (commonly known as bits per pixel or bpp). This corresponds to 8 bits each for red, green, and blue, giving a range of 256 possible values, or intensities, for each color. With this system, approximately 16.7 million discrete colors can be reproduced.
RGB is a type of component video signal used in the video electronics industry. It consists of three signals - red, green and blue - carried on three separate cables. Extra cables are sometimes needed to carry synchronising signals. RGB signal formats are often based on modified versions of the RS-170 and RS-343 standards for monochrome video. This type of video signal is widely used in Europe since it is the best quality signal that can be carried on the standard SCART connector. Outside Europe, RGB is not very popular as a video signal format – S-Video takes that spot in most non-European regions. However, almost all computer monitors around the world use RGB.
Proper reproduction of colors in professional environments requires extensive color calibration of all the devices involved in the production process. This results in several transparent conversions between device-dependent color spaces during a typical production cycle in order to ensure color consistency throughout the process. Along with the creative processing, all such interventions on digital images inherently damage it by reducing its gamut. Therefore the denser the gamut of the original digitized image, the more processing it can support without visible degradation. Professional devices and software tools allow for 48 bpp images to be manipulated (16 bits per channel) in order to increase the density of the gamut.
Colors used in web design are commonly specified using RGB; see web colors for an explanation of how colors are used in HTML and related languages. Initially, the limited screen resolution of most monitors led to a limited color palette of 216 RGB colors - defined by the Netscape Color Cube. However, with the predominance of higher resolution screens now available, the use of the full 16.7 million colors of the HTML RGB color code no longer poses problems for most viewers.
The RGB color model for HTML was formally adopted as an Internet standard in HTML 3.2, however it had been in use for some time before that.
