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Additive color
Additive color
Additive color
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Red, green, and blue lights combining by reflecting from a white wall: secondary colors yellow, cyan, and magenta are found at the intersections of red and green, green and blue, and blue and red. The intersection of all three primary colors together yields white.
James Clerk Maxwell, with his color top that he used for investigation of color vision and additive color

Additive color or additive mixing is a property of a color model that predicts the appearance of colors made by coincident component lights, i.e. the perceived color can be predicted by summing the numeric representations of the component colors.[1] Modern formulations of Grassmann's laws[2] describe the additivity in the color perception of light mixtures in terms of algebraic equations. Additive color predicts perception and not any sort of change in the photons of light themselves. These predictions are only applicable in the limited scope of color matching experiments where viewers match small patches of uniform color isolated against a gray or black background.

Additive color models are applied in the design and testing of electronic displays that are used to render realistic images containing diverse sets of color using phosphors that emit light of a limited set of primary colors. Examination with a sufficiently powerful magnifying lens will reveal that each pixel in CRT, LCD, and most other types of color video displays is composed of red, green, and blue light-emitting phosphors which appear as a variety of single colors when viewed from a normal distance.

Additive color, alone, does not predict the appearance of mixtures of printed color inks, dye layers in color photographs on film, or paint mixtures. Instead, subtractive color is used to model the appearance of pigments or dyes, such as those in paints and inks.

The combination of two of the common three additive primary colors in equal proportions produces an additive secondary color—cyan, magenta or yellow. Additive color is also used to predict colors from overlapping projected colored lights often used in theatrical lighting for plays, concerts, circus shows, and night clubs.[3]

The full gamut of color available in any additive color system is defined by all the possible combinations of all the possible luminosities of each primary color in that system. In chromaticity space, a gamut is a plane convex polygon with corners at the primaries. For three primaries, it is a triangle.

History

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The first permanent color photograph, taken by Thomas Sutton, under the direction of James Clerk Maxwell in 1861

Systems of additive color are motivated by the Young–Helmholtz theory of trichromatic color vision, which was articulated around 1850 by Hermann von Helmholtz, based on earlier work by Thomas Young. For his experimental work on the subject, James Clerk Maxwell is sometimes credited as being the father of additive color.[4] He had the photographer Thomas Sutton photograph a tartan ribbon on black-and-white film three times, first with a red, then green, then blue color filter over the lens. The three black-and-white images were developed and then projected onto a screen with three different projectors, each equipped with the corresponding red, green, or blue color filter used to take its image. When brought into alignment, the three images (a black-and-red image, a black-and-green image and a black-and-blue image) formed a full-color image, thus demonstrating the principles of additive color.[5]

See also

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Additive color mixing with CD covers

References

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Additive color

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from Grokipedia
Additive color is a model of color and mixing in which colors are produced by the superposition of waves of different wavelengths, starting from (no ) and adding primary colored lights to create a of hues, with full combination yielding . The primary colors in this system are , , and (commonly abbreviated as RGB), selected because they correspond to the peak sensitivities of the three types of cells in the —long-wavelength (-sensitive), medium-wavelength (-sensitive), and short-wavelength (-sensitive) —which enable trichromatic vision. Mixing two primaries produces secondary colors: and yield , and yield , and and yield , while equal intensities of all three primaries stimulate the cones uniformly to perceive . This additive principle contrasts with mixing, used in pigments and inks, where colors are created by selectively absorbing wavelengths from white rather than emitting them. In practice, additive color models underpin modern display technologies, such as computer monitors, televisions, projectors, and LED screens, where pixels composed of , , and subpixels emit in varying intensities to approximate any visible color through precise control via the equation for color matching: any perceivable color S=aR+bG+cBS = aR + bG + cB, with aa, bb, and cc representing the intensities of the primaries. Applications extend to and , where the model's ability to generate a wide of colors—over 16 million in standard RGB systems—relies on the additive superposition of without loss of intensity. Historically, the foundations of additive color theory emerged in the through scientific inquiries into human vision and , influencing artistic techniques like , as explored by , who drew from Ogden Rood's 1879 work Modern Chromatics to achieve optical mixing via juxtaposed colored dots that blend additively in the viewer's eye. Today, the RGB model remains central to fields like and , though variations such as standardize it for consistent color reproduction across devices.

Fundamentals

Definition

Additive color is a process of mixing colored lights of different wavelengths to create new colors, where the combination of primary lights—, , and —results in white when added together at full intensity. This method relies on the emission and superposition of rather than the reflection or absorption of it, allowing for the direct creation of a wide of hues through the blending of these primaries. From a physical perspective, additive color mixing occurs because consists of photons or electromagnetic that add together upon combination, with no absorption or of wavelengths as seen in pigment-based systems. The resulting color at any point is determined by the total intensity and spectral composition of the overlapping s, enabling precise control in applications involving emitted . The terminology "additive" derives from the fundamental principle of summing the intensities of the individual sources to form the perceived color, distinguishing it from subtractive processes that remove components. For example, projecting overlapping beams of and produces , as the eye integrates the added wavelengths into a single intermediate hue. The RGB primaries form the basis of most additive color systems, providing a foundational framework for color reproduction.

Principles of Light Mixing

Human is based on the trichromatic , which posits that the contains three types of photoreceptors, each maximally sensitive to different ranges corresponding approximately to (long wavelengths around 564 nm), (medium wavelengths around 534 nm), and (short wavelengths around 420 nm). These s enable the perception of a wide of colors through the relative stimulation of each type, where the brain interprets the combined signals to construct color sensations. In additive color mixing, light from different sources combines by superimposing their spectral power distributions, resulting in a total intensity at each that is the linear sum of the individual components. For monochromatic lights in , , and bands, the resultant is given by Itotal(λ)=Ir(λ)+Ig(λ)+Ib(λ),I_{\text{total}}(\lambda) = I_r(\lambda) + I_g(\lambda) + I_b(\lambda), where Ir(λ)I_r(\lambda), Ig(λ)I_g(\lambda), and Ib(λ)I_b(\lambda) represent the intensity functions of the respective primary lights as a function of λ\lambda. This superposition occurs because light waves do not interfere destructively in typical viewing conditions, allowing intensities to add directly at the . A key consequence of this mechanism is metamerism, where distinct combinations of spectra can produce identical color perceptions due to the limited sensitivity of the three types, which effectively integrate the input into three tristimulus values. For instance, a pure light at 580 nm may appear indistinguishable from a mixture of and lights to the , as both stimulate the long- and medium-wavelength cones in the same proportions, even though their underlying spectra differ. These principles are formalized in Grassmann's laws of color addition, which describe the linear algebra underlying color matching under photopic conditions. The law of additivity states that if two pairs of lights match (A matches B, and C matches D), then the mixture of A and C matches the mixture of B and D. The law of proportionality asserts that scaling the intensities of all components in a color match by the same factor preserves the match. Additionally, the law of continuity implies that small, continuous variations in the spectral composition lead to gradual changes in perceived , supporting the of . These laws hold approximately for additive mixtures and underpin quantitative . When the three primaries are combined at equal intensities, the result approximates white light, known as the , as the balanced stimulation of all types mimics the broad- response to natural daylight. This occurs because the summed closely matches the eye's integrated sensitivity across the visible range, producing achromatic .

Color Models

RGB Model

The is an additive color representation that utilizes three primary channels—red (R), (G), and (B)—to specify colors through varying intensities of . Each channel is typically encoded with 8 bits, allowing 256 discrete levels (values from 0 to 255) per channel, which enables the reproduction of approximately 16.7 million distinct colors in a 24-bit system. This structure forms the foundation for , where values are defined by the triplet (R, G, B). The primary colors in the RGB model approximate monochromatic light sources with peak wavelengths of at approximately 700 nm, green at 546 nm, and at 436 nm, corresponding to the classic CIE 1931 RGB primaries derived from human color matching experiments. These wavelengths reflect the trichromatic basis of human vision, where combinations of these primaries can match a wide range of spectral colors, though real-world implementations like displays use filtered broadband sources tuned to similar perceptual points. In terms of color gamut, the RGB model is often represented within the CIE 1931 xy chromaticity diagram, with serving as a standardized subset defined by specific primary chromaticities (: x=0.6400, y=0.3300; : x=0.3000, y=0.6000; : x=0.1500, y=0.0600) and a D65 (x=0.3127, y=0.3290). This gamut covers about 35% of the visible CIE 1931 color space, prioritizing compatibility for consumer displays and web content while ensuring reproducible colors across devices. To convert RGB values to perceived colors in a device-independent space, linear RGB intensities are transformed to CIE XYZ tristimulus values using a 3x3 matrix derived from the primaries and white point: [XYZ]=[0.41240.35760.18050.21260.71520.07220.01930.11920.9505][RlinearGlinearBlinear]\begin{bmatrix} X \\ Y \\ Z \end{bmatrix} = \begin{bmatrix} 0.4124 & 0.3576 & 0.1805 \\ 0.2126 & 0.7152 & 0.0722 \\ 0.0193 & 0.1192 & 0.9505 \end{bmatrix} \begin{bmatrix} R_{\text{linear}} \\ G_{\text{linear}} \\ B_{\text{linear}} \end{bmatrix}
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