According to AbbreviationFinder, RGB stands for Red, Green, Blue; red, green, blue. It refers to the composition of color in terms of the intensity of the primary colors with which these colors are formed.
Concept
It is a color model based on additive synthesis, with which it is possible to represent a color by mixing by adding the three primary light colors. The RGB color model does not define by itself what exactly red, green, or blue means, so the same RGB values can display noticeably different colors on different devices that use this color model. Even if they use the same color model, their color spaces can vary considerably.
Proportions with which each color is mixed
To indicate with what proportion each color is mixed, a value is assigned to each of the primary colors, so that the value 0 means that it does not intervene in the mixture and, as that value increases, it is understood that it contributes more intensity To the mix. Although the range of values could be anything (real values between 0 and 1, integer values between 0 and 37, and so on), it is common for each primary color to be encoded with one byte (8 bits). Thus, in a usual way, the intensity of each of the components is measured according to a scale that goes from 0 to 255.
RGB cube
Therefore, red is obtained with (255,0,0), green with (0,255,0) and blue with (0,0,255), obtaining, in each case, a monochromatic resulting color. The absence of color – what is known as black color – is obtained when the three components are 0, (0,0,0). The combination of two colors at level 255 with a third at level 0 gives rise to three intermediate colors. Thus yellow is (255,255,0), cyan (0,255,255) and magenta (255,0,255). Obviously, the white color is formed with the three primary colors at their highest level (255,255,255).
The set of all colors can be represented in the form of a cube. Each color is a point on the surface or inside it. The gray scale would be located on the diagonal that joins white with black.
Color on computer screens
On computer screens, the sensation of color is produced by the additive mixing of red, green, and blue. There are a series of tiny dots called pixels. Each point on the screen is a pixel and each pixel is actually a set of three sub-pixels; one red, one green and one blue, each of which glows with a certain intensity.
At first, the limitation on the color depth of most monitors led to a limited gamut of 216 colors, defined by the color cube. However, the dominance of 24-bit monitors made it possible to use 16.7 million colors from the HTML RGB color space.
The range of colors on the web consists of 216 combinations of red, green and blue, where each color can take one of six different values (in hexadecimal): # 00, # 33, # 66, # 99, #CC or #FF. You can see 63 gives the number of combinations, 216. These values in decimal correspond to 0, 51, 102, 153, 204 and 255, which have an intensity percentage of 0%, 20%, 40%, 60%, 80% and 100%, respectively. This allows the 216 colors to be divided into a cube of dimension 6.
It is intended that the pixels are of a color the more saturated the better, but it is never an absolutely pure color. Therefore, the production of colors with this system has a double limitation:
- The derivative of the operation of additive mixtures: only the interior colors of the triangle formed by the three light sources can be obtained.
- The derivative of the fact that the primary colors used are not absolutely monochromatic.
- In addition, the various screens are not exactly the same, in addition to being configurable by users, with which various parameters may vary.
This implies that the color codings intended for the displays should be interpreted as relative descriptions, and the accuracy understood according to the characteristics of the display.
Color perception and sensation
The eyes have two types of light-sensitive cells or photoreceptors: rods and cones. The latter are responsible for providing the color information. To know how a color is perceived, it must be taken into account that there are three types of cones with different frequency responses, and that they have maximum sensitivity to the colors that make up the RGB triple, red, green and blue.
While the cones, which receive information from green and red, have a similar sensitivity curve, the response to blue is one twentieth (1/20) of the response to the other two colors. This fact is taken advantage of by some image and video coding systems, such as JPEG or MPEG, consciously “losing” more information from the blue component, since the eyes will not perceive this loss.
The sensation of color can be defined as the response of each of the sensitivity curves to the spectrum radiated by the observed object. In this way, you get three different answers, one for each color.
The fact that the sensation of color is obtained in this way means that two observed objects, radiating a different spectrum, can produce the same sensation. And the color synthesis model is based on this limitation of human vision, through which it can be obtained from studied visual stimuli and with a mixture of the three primary colors, the color of an object with a certain spectrum.
Luminance signal
The sensation of luminosity is given by the brightness of an object and by its opacity, being able to produce two objects with different shades and prisms the same luminous sensation. The luminance signal is the quantification of that sensation of brightness. To maintain compatibility between black and white images and color images, current television systems (PAL, NTSC, SECAM) transmit three pieces of information: luminance and two color difference signals.
In this way, the old black and white models can ignore the information related to the color, and reproduce only the luminance, that is, the brightness of each pixel applied to a grayscale image. And color televisions obtain the information of the three RGB components from a matrix that relates each component to one of the color difference signals. For each of the television systems they are transmitted differently, which is why you can have problems when reproducing an NTSC signal in a PAL reproduction system.
