Jump to content

RGB color model

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by Michael Hardy (talk | contribs) at 21:38, 17 March 2004. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.



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 blue light 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.

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.

When written, RGB values in 24 bpp are commonly specified using three integers between 0 and 255, each representing red, green, and blue intensities, in that order. For example:

There is also a 16 bpp mode, in which there are either 5 bits per color, called 555 mode, or an extra bit for green (because the eye can see more shades of green than of other colors), called 565 mode. The 24 bpp mode is typically called Truecolor, while the 16 bpp mode is called HiColor.

With the need for compositing images came a variant of RGB which includes an extra 8 bit channel for transparency, thus resulting in a 32 bpp format. The transparency channel is commonly known as the alpha channel, so the format is named RGBA. Please note that since it doesn't change anything in the RGB model, RGBA is not a distinct color model, it's only a file format which integrates transparency information along with the color information in the same file.

The intensity of the color output on computer display devices isn't always linear. That is, even though a value of 127 is very close to halfway between zero and 255, the color output of a computer display device when displaying (127, 127, 127) is often significantly less than halfway between the black level and white point of the display. This is because most display devices have a gamma characteristic different from 1 (i.e. the behavior of most display devices is not linear in the relationship between color value and output intensity), and require gamma correction.

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.

See also color model, List of colors, HSV color space, HLS color space, YUV

History of RGB color model

The use of the RGB color model as the standard for presentation of color on the Internet has its roots in the 1953 RCA color-tv standards and in Edwin Land's use of an RGB standard in the Land / Polaroid camera. The RGB color model was formally adopted as an Internet standard with the adoption of HTML 3.2.

3-dimensional mathematics of light and color

The RGB color model is also at the center of the Virtual Light & Colour Cubes - dedicated as Peace Cubes in 1997 - that embody a three-dimensional RGB mathematics of light and color in an evolving open source curriculum in the elements of light and color.

Video electronics

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.

Retrieved from "https://en.wikipedia.org/w/index.php?title=RGB_color_model&oldid=2818446"