värikulma

Värikulma, also known as the *color angle* or *hue angle*, is a concept used in color theory and colorimetry to describe the position of a color within the chromaticity diagram, specifically the CIE 1931 color space. It is measured in degrees and represents the angle formed between the reference white point and the color point on the CIE chromaticity diagram, which plots colors based on their x and y coordinates.

The CIE chromaticity diagram is a two-dimensional representation of human color perception, where the x and y coordinates correspond to the trichromatic stimulus values (CIE XYZ color space). The outer boundary of the diagram represents all possible spectral colors, while the inner region includes all possible colors that can be perceived. The reference white point, typically D65 or E, serves as the origin for measuring the hue angle.

To calculate the värikulma, the arctangent of the ratio between the y and x coordinates of a color point is used, adjusted for the quadrant in which the point lies. The formula is generally expressed as:

värikulma = arctan((y / x) * (1 - x) / y)

However, a more precise method involves converting the CIE xy coordinates to a hue angle using the following steps:

1. Calculate the intermediate values: r = (1 - x) / y and g = (y - y') / (x - x'), where (x', y') is the reference white point.

2. Determine the hue angle based on the quadrant of the color point, accounting for the spectral nature of colors.

Värikulma is particularly useful in fields such as graphic design, digital imaging, and color science, where precise color communication and manipulation are required. It helps in understanding how colors relate to one another in terms of hue, making it easier to select complementary or analogous colors for design purposes. The concept also aids in color space conversions and ensures consistency in color reproduction across different media.