The RGB Color Model

We live in a world in which colors play an important role – and that’s nothing new. Goethe con­sid­ered his 1810 work on color (“Theory of Colors”) to be more sig­nif­i­cant than his literary works for example. And in 1809, British oph­thal­mol­o­gist and physicist Thomas Young (1773–1829) put forward the theory that all the spectral colors could be produced by combining three primary colors. However, there was no talk of RGB at this point. Young’s claim was only proved 50 years later, by Scottish scientist James Clerk Maxwell (1831–1879). Maxwell produced the first color pho­to­graph in 1861 and is credited with proving the theory of additive color mixing.

Colors give signals, make things appear a certain way, and appeal to the senses. Strictly speaking, that’s exactly what color is – a sensory im­pres­sion of the light that we can see. It is elec­tro­mag­net­ic radiation with a wave­length ranging from 380 nanome­ters (purple) to 760 nanome­ters (red). As various image rep­re­sen­ta­tion tech­nolo­gies have developed, so have several models for the optical rep­re­sen­ta­tion of colors. With the emergence of color screens, the RGB color model has played a key role in how images are re­pro­duced on elec­tron­ic output devices. This guide covers all the most important in­for­ma­tion about RGB colors.

The RGB color space uses the three basic colors that the light-sensitive cones in our eyes react most to – red, green, and blue. The basis of this color system is black. All the colors are seen in contrast with black. The term additive color mixing comes from the fact that every RGB color is made by combining – or adding together – the three basic colors. On a computer screen, in­di­vid­ual dots (pixels) are displayed alongside one another to form an image. Each pixel consists of three sub-pixels (one red, one green, and one blue), which our eyes mix so that we see a single color.

On the internet, all these colors can be expressed using hexa­dec­i­mal codes as well as RGB values. In fact, Cascading Style Sheets (CSS) often use both systems to ensure that colors are displayed correctly in different browsers.

The graphics formats used to display images and graphics online are all based on RGB colors, except GIF. Image editing software like Photoshop and free image editing programs also have an RGB mode to display colors. And image com­pres­sion tools use RGB when com­press­ing images for websites to boost per­for­mance.

Of course! There are many different color space concepts. Each re­pro­duces colors in a slightly different way. Al­ter­na­tive color spaces include:

CIE is the standard valance system created in 1931 using average values for standard observers. CIE 1964 considers the field of view of the human eye, which is equiv­a­lent to an A4 sheet of paper seen from a distance of 30 cm. Other color spaces were later derived from this (CIELUC, CIELAB and CIEUVW).

The sRGB color space is a modified version of the RGB color space, developed by several companies es­pe­cial­ly for the internet. It is used in open-source programs and for the SVG image format. Adobe designed a color space called Adobe RGB to reproduce the colors of a CMYK printer on a computer screen. There are a great number of RGB color spaces out there, each designed with specific display purposes in mind. In fact, anyone with the right skills can create their very own color space.

The HSV (also known as HSB) color space describes colors by their hue (H), sat­u­ra­tion (S) and bright­ness value (V or B). It is closer to how the human eye perceives color. There are two other similar color spaces: HSL and HSI. Here, the L stands for “lightness” and the I stands for “intensity”. HSL can be used in CSS.

This type of color space is used for color tele­vi­sion standards such as NTSC, PAL and SECAM. Examples include YIQ, YUV, YDbDr, YPbPr and YCbCr. They combine two color values with one bright­ness value. There is also a newer, extended color space for digital video signals called xvYCC.