Hue to Rgb Converter

Hue is the angular coordinate of a cylindrical remapping of the RGB cube. Pure red sits at 0 degrees, pure green at 120 degrees and pure blue at 240 degrees, with the additive secondaries yellow, cyan and magenta at 60, 180 and 300 degrees. Because a cylinder cannot describe a cube on its own, hue must be combined with saturation and lightness before an RGB triple can be recovered. The conversion first computes chroma, C = (1 - |2L - 1|) x S, which is the width of the RGB range that the requested lightness can support: chroma peaks at L = 0.5 and collapses to zero at pure black or pure white. The intermediate term X = C x (1 - |(H/60) mod 2 - 1|) linearly interpolates the middle channel across each 60-degree sector, and the offset m = L - C/2 lifts the whole triple so that its midpoint lands on the requested lightness. Practical ranges matter more than the algebra. At S = 0 the hue angle is meaningless: HSL(0, 0 percent, 50 percent) and HSL(180, 0 percent, 50 percent) both resolve to RGB(128, 128, 128), so hue is undefined for any neutral gray and is conventionally reported as 0. HSL is also not perceptually uniform. Yellow at HSL(60, 100 percent, 50 percent) carries a relative luminance near 0.93 while blue at HSL(240, 100 percent, 50 percent) sits near 0.07, even though the two share identical saturation and lightness numbers. Designers who need even-looking steps should work in a perceptual space such as CIELAB or OKLCH and treat HSL as a convenience layer. Rounding to 8-bit integers also means many distinct hue angles collapse onto the same hex value, particularly at low saturation.

The circular arrangement of hue dates to Isaac Newton, who in his 1704 Opticks bent the linear spectrum into a ring and closed the gap between red and violet with purples that have no single wavelength. Albert Munsell formalised the idea into a measured three-axis solid of hue, value and chroma in his 1905 A Color Notation, giving colour its first widely used numerical notation. The specific cylindrical models used in computing arrived with computer graphics: Alvy Ray Smith described the HSV hexcone at SIGGRAPH in 1978, and George Joblove and Donald Greenberg presented the closely related lightness-based double-hexcone model in the same 1978 proceedings. Both were designed so that artists could pick colours by naming a family, a purity and a brightness rather than by guessing three channel intensities. The HSL variant reached the web through CSS. The hsl() and hsla() notations were standardised in CSS Color Module Level 3, which reached W3C Recommendation status in 2011 after years of browser support, and the sector-based conversion described above is the algorithm the specification requires. CSS Color Module Level 4 later added space-separated syntax, an optional slash-alpha form, and automatic wrapping of out-of-range angles so that hsl(390 70 percent 50 percent) resolves to 30 degrees. The same level of the specification introduced lch() and oklch(), an acknowledgement that the 1978 cylinders are convenient but perceptually uneven, and that hue rotation in a perceptual space produces more consistent palettes than rotation in HSL.