or traditional artists' models based on tints and shades (). Furthermore, neither additive nor subtractive color models define color relationships the same way the human eye does. For example, imagine we have an RGB display whose color is controlled by three sliders ranging from , one controlling the intensity of each of the red, green, and blue primaries. If we begin with a relatively colorful orange , with sRGB values , , , and want to reduce its colorfulness by half to a less saturated orange , we would need to drag the sliders to decrease R by 31, increase G by 24, and increase B by 59, as pictured below. In an attempt to accommodate more traditional and intuitive color mixing models, computer graphics pioneers at PARC and NYIT introduced the HSV model for computer display technology in the mid-1970s, formally described by Alvy Ray Smith in the August 1978 issue of Computer Graphics. In the same issue, Joblove and Greenberg described the HSL model—whose dimensions they labeled hue, relative chroma, and intensity—and compared it to HSV (). Their model was based more upon how colors are organized and conceptualized in human vision in terms of other color-making attributes, such as hue, lightness, and chroma; as well as upon traditional color mixing methods—e.g., in painting—that involve mixing brightly colored pigments with black or white to achieve lighter, darker, or less colorful colors. The following year, 1979, at SIGGRAPH, Tektronix introduced graphics terminals using HSL for color designation, and the Computer Graphics Standards Committee recommended it in their annual status report (). These models were useful not only because they were more intuitive than raw RGB values, but also because the conversions to and from RGB were extremely fast to compute: they could run in real time on the hardware of the 1970s. Consequently, these models and similar ones have become ubiquitous throughout image editing and graphics software since then. Some of their uses are described below. Formal derivation Color-making attributes The dimensions of the HSL and HSV geometries—simple transformations of the not-perceptually-based RGB model—are not directly related to the photometric color-making attributes of the same names, as defined by scientists such as the CIE or ASTM. Nonetheless, it is worth reviewing those definitions before leaping into the derivation of our models. For the definitions of color-making attributes which follow, see: Hue The "attribute of a visual sensation according to