Bell HSL

Bell HSL (Hue, Saturation, Lightness) is a color space representation method developed by Bell Telephone Laboratories. It is a cylindrical-coordinate representation of points in an RGB color model, intended to approximate human perception of color attributes. HSL defines colors in terms of three components:

• Hue: This represents the dominant wavelength of the color. It is typically measured in degrees, ranging from 0 to 360. Red is usually defined as 0 degrees, green as 120 degrees, and blue as 240 degrees. Hue is often visualized as a color wheel.

• Saturation: This represents the amount of grayness or purity of the color. A saturation of 0% means the color is a shade of gray, while a saturation of 100% means the color is pure and intense. Saturation is often referred to as chroma.

• Lightness: This represents the perceived brightness of the color. It ranges from 0% (black) to 100% (white). A lightness of 50% is typically considered "normal". Lightness is sometimes called luminance.

Bell HSL, while related to, is distinct from other HSL and HSV (Hue, Saturation, Value) color models. Specific details about the original Bell Labs implementation, and any algorithms used for converting between RGB and Bell HSL, are difficult to obtain due to limited historical documentation. However, it's understood that Bell HSL attempted to create a perceptually uniform color space to improve color representation in their video and telecommunications systems.

The model’s primary goal was to provide a more intuitive way for users to specify and manipulate colors compared to RGB. By separating color into hue, saturation, and lightness, Bell HSL allowed for easier adjustment of color characteristics without affecting other aspects of the color. While superseded by other HSL and HSV implementations and CIE color spaces, Bell HSL represents an important step in the development of color science and the pursuit of perceptually accurate color representation.