Color Mixing - Wikipedia

Additive model

edit Main article: Additive color

 

Additive mixing combines two or more colors into a mixture with brightness equal to the sum of the components' brightnesses.[1]: 4.4  An ideal physical model to demonstrate the additive model comprises two superimposed colored lights aimed at the observer. The additive model is usually demonstrated by reflecting two beams of colored light off a white, matte surface (e.g. projectors) or by analyzing the sub-pixels of a color display, both of which follow the additive model closely.

The most common additive color model is the RGB color model, which uses three primary colors: red, green, and blue. This model is the basis of most color displays. Some modern displays are multi-primary color displays, which have 4-6 primaries (RGB, plus cyan, yellow and/or magenta) in order to increase the size of the color gamut. For all additive color models, the absence of all primaries results in black. For practical additive color models, an equal superposition of all primaries results in neutral (gray or white). In the RGB model, an equal mixture of red and green is yellow, an equal mixture of green and blue is cyan and an equal mixture of blue and red is magenta.[1]: 4.2  Yellow, cyan and magenta are the secondary colors of the RGB model.

Subtractive model

edit Main article: Subtractive color

 

Subtractive mixing combines two or more colors into a mixture with brightness lower than either of the two components' brightnesses. An ideal physical model to demonstrate the subtractive model comprises a white light transmitting through two colored filters, each of which subtract a portion of the white light, transmitting a light of the combined color.[1]: 5.2  However, the subtractive model is usually demonstrated with dyes or pigments, such as paint or ink, which often do not closely follow the subtractive model, instead requiring a more complex model such as Kubelka–Munk theory. How well they follow the model depends mostly on the opacity of the pigment or dye.[1]: 6.1 

The most common subtractive color models are the CMYK color model, CMY color model and RYB color model.[1]: 6.2  The CMYK model used in color printing uses cyan, magenta, yellow, and black primaries. For all subtractive color models, the absence of all color primaries results in white. For ideal subtractive color models, an equal superposition of all primaries results in a neutral (dark gray or black). The CMYK model adds a black primary to improve the darkness of blacks, where the CMY model can only mix to dark gray or only achieves black inefficiently, i.e. by using lots of the primary pigments. In the CMY model, an equal mixture of cyan and magenta is blue, an equal mixture of magenta and yellow is red and an equal mixture of yellow and cyan is green. These mixtures are the secondary colors of the CMY model, which are the same as the primaries of the additive RGB model and vice versa.

Average model

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Average mixing (sometimes additive-average) combines two colors into a mixture with brightness equal to the average of the two components' brightnesses.[1]: 4.4  This model is often demonstrated with a Newton disc, where a wheel comprising several color wedges along the circumference is rotated at high speed, such that the human eye cannot temporally differentiate the colors, and they combine to a color with the average brightness (weighted to the angle each color takes up). Another physical model mimics pointillism or halftone printing, where the spatial acuity of the human eye is not sufficient to spatially differentiate the colors, and they combine to a mixture with the average brightness.[1]: 4.4  There are no common color models that explicitly use the average model, though many additive or subtractive models can be described in part by the average model.