What is RGB (Red, Green, Blue)?

RGB (Red, Green, Blue) refers to the color composition in terms of the density of the primary colors from which the colors are created.

RGB Definition and Colors

What is RGB (Red, Green, Blue) Model?

It is a color model based on additive synthesis, where it is possible to represent a color by adding and mixing the three primary colors of light.

The RGB color model does not define precisely what red, green, or blue means. Therefore, the same RGB values ​​​​can show significantly different colors on different devices using this color model. Even if they use the same color model, color spaces can vary considerably.

Ratios in which Every Color is Blended

A value is assigned to each primary color to specify the ratio in which each color is mixed. Thus, a value of 0 means that it does not interfere with the mixture, and the higher this value is understood to contribute more intensity.

Although the range of values ​​can be any value (absolute values ​​between 0 and 1, integer values ​​between 0 and 37), it is expected to encode each primary color with a byte (8 bits). Thus, in the usual way, the intensity of each of the components is measured according to a scale ranging from 0 to 255.

Thus, (255,0,0) gives red, (0,255,0) gives green, and (0,0,255) gives blue, in each case resulting in a monochromatic color. The absence of the color known as black is obtained when the three components are 0, (0,0,0). The combination of two colors at level 255 with a third color at level 0 gives three intermediate colors.

Remember the following color codes: yellow (255,255,0), cyan (0,255,255), and magenta (255,0,255). Obviously, white color is created with the three primary colors at the maximum level (255,255,255).

All colors can be represented in a cube. Each color is a point on the surface or inside. Grayscale is located on the diagonal that connects white to black.

RGB Color on Computer Screens

On computer screens, the sensation of color is produced by an additive mixture of red, green, and blue. There are a series of tiny dots called pixels. Each dot on the screen is a pixel, and each pixel is actually a set of three subpixels. One red, one green, and one blue, each glowing at a certain intensity.

Initially, the limitation in color depth of most monitors led to a limited range of 216 colors defined by the color cube. However, the dominance of 24-bit monitors has made it possible to use 16.7 million colors from the HTML RGB color space.

The web’s color palette consists of 216 combinations of red, green, and blue, where each color can take on a value (in hexadecimal) among six different colors: #00, #33, #66, #99, #CC, or #FF. You can see that 63 gives the number of 216 combinations.

These decimal values ​​correspond to 0, 51, 102, 153, 204, and 255, which are the density percentages of 0%, 20%, 40%, 60%, 80%, and 100%, respectively. This allows the 216 colors to be divided into a cube of size 6.

The more saturated the pixels, the better. But it is certainly not a pure color. Therefore, the reproduction of colors with this system has two limitations:

  • A derivative of the work of the admixture mixtures: only the inner colors of the triangle formed by three light sources can be obtained.
  • This is a derivative of the fact that the primary colors used are absolutely not monochrome.
  • In addition, besides being configurable by users where various screens can change, multiple screens are not the same.

This means that screen color coding should be interpreted as relative descriptions, and accuracy should be understood based on the characteristics of the screen.

Color Perception and Feeling

There are two types of light-sensitive cells or photoreceptors in the eyes: rods and cones. The latter is responsible for providing color information.

To know how a color is perceived, it should be noted 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 triplets: red, green, and blue.

While the cones that receive information from green and red have a similar sensitivity curve, the response to the color blue is the twentieth (1/20) of the reaction to the other two colors.

This fact is used by some image and video encoding systems, such as JPEG or MPEG, because they consciously “lose” more information about the blue component because the eyes will not perceive this loss.

The color sensation can be defined as the response of each of the sensitivity curves to the spectrum emitted by the observed object. In this way, three different responses are obtained, one for each color.

This way of obtaining the color sensation means that two observed objects emitting a different spectrum can produce the same sensation.

This limitation of human vision is based on the model of color synthesis, according to which it is possible to obtain the color of an object with a particular spectrum, which is a mixture of the three primary colors and the visual stimuli examined.

RGB Brightness Signal

The sense of brightness is given by the brightness and opacity of an object, and two objects with different tones and prisms can produce the same sense of light. The brightness signal is the quantity of this sense of brightness.

To ensure compatibility between black and white images and color images, current television systems (PAL, NTSC, SECAM) transmit three pieces of information: the brightness and two color difference signals.

In this way, old black-and-white models can ignore the color information and produce only the brightness, that is, the brightness of each pixel applied to a grayscale image.

Color televisions receive the information of the three RGB components from a matrix that associates each element with one of the color difference signals. They are transmitted differently for each television system, so there may be problems producing an NTSC signal in a PAL reproduction system.

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