Primary color

A set of primary colors is, most tangibly, a set of real colorants or colored lights that can be combined in varying amounts to produce a gamut of colors. This is the essential method used in applications that are intended to elicit the perception of diverse sets of color, e.g. electronic displays, color printing, and paintings. Perceptions associated with a given combination of primary colors are predicted by applying the appropriate mixing model (additive, subtractive, additive averaging, etc.) that embodies the underlying physics of how light interacts with the media and ultimately the retina. A set of primary colors is, most tangibly, a set of real colorants or colored lights that can be combined in varying amounts to produce a gamut of colors. This is the essential method used in applications that are intended to elicit the perception of diverse sets of color, e.g. electronic displays, color printing, and paintings. Perceptions associated with a given combination of primary colors are predicted by applying the appropriate mixing model (additive, subtractive, additive averaging, etc.) that embodies the underlying physics of how light interacts with the media and ultimately the retina. Primary colors can also be conceptual, either as additive mathematical elements of a color space or as irreducible phenomenological categories in domains such as psychology and philosophy. Color-space primaries are precisely defined and empirically rooted in psychophysical color matching experiments which are foundational for understanding color vision. Primaries of some color spaces are complete (that is, all visible colors are described in terms of their weighted sums with nonnegative weights) but necessarily imaginary (that is, there is no plausible way that those primary colors could be represented physically, or perceived). Phenomenological accounts of primary colors, such as the psychological primaries, have been used as the conceptual basis for practical color applications even though they are not a quantitative description in and of themselves. All sets of real and color-space primaries are arbitrary, in the sense that there is no one set of primaries that can be considered the canonical set. Primary pigments or light sources selected for a given application on the basis of subjective preferences as well as practical factors such as cost, stability, availability etc. Color-space primaries can be subjected to meaningful one-to-one transformations so that the transformed space is still complete and each color is specified with a unique sum. Elementary art education materials, dictionaries, and electronic search engines often define primary colors effectively as conceptual colors (generally red, yellow, and blue; or red, green, and blue) that can be used to mix 'all' other colors and often go further and suggest that these conceptual colors correspond to specific hues and precise wavelengths. Such sources do not present a coherent, consistent definition of primary colors since real primaries cannot be complete. The perception elicited by multiple light sources co-stimulating the same area of the retina is additive, i.e., predicted via summing the spectral power distributions or tristimulus values of the individual light sources (assuming a color matching context). For example, a purple spotlight on a dark background could be matched with coincident blue and red spotlights that are both dimmer than the purple spotlight. If the intensity of the purple spotlight was doubled it could be matched by doubling the intensities of both the red and blue spotlights that matched the original purple. The principles of additive color mixing are embodied in Grassmann's laws. Additive mixing of coincident spot lights was applied in the experiments used to derive the CIE 1931 colorspace. The original monochromatic primaries of the (arbitrary) wavelengths of 435.8 nm (violet), 546.1 nm (green), and 700 nm (red) were used in this application due to the convenience they afforded to the experimental work. Red, green, and blue light are popular primaries for additive color mixing since primary lights with those hues provide a large triangular chromaticity gamut. Small red, green, and blue elements in electronic displays mix additively from an appropriate viewing distance to synthesize compelling colored images. The exact colors chosen for additive primaries are a technological compromise between the available phosphors (including considerations such as cost and power usage) and the need for large chromaticity gamut. The ITU-R BT.709-5/sRGB primaries are typical. It is important to note that additive mixing provides very poor predictions of color perception outside the color matching context. Well known demonstrations such as The dress and other examples show how the additive mixing model alone is not sufficient for predicting perceived color in many instances of real images. In general, we cannot completely predict all possible perceived colors from combinations of primary lights in the context of real-world images and viewing conditions. The cited examples suggest just how remarkably poor such predictions can be.