Physical Paint Gamuts & Convex Hull Mixing
In traditional studio painting (oil, gouache, acrylic, watercolor), an artist does not have access to an abstract digital RGB color wheel. You have a physical palette with specific tubes of paint (e.g. Ultramarine Blue PB29, Yellow Ochre PY43, Burnt Sienna PR101, Titanium White PW6).
Every possible color you can physically mix from those tubes lies inside the Convex Hull formed by those pigments' spectral coordinates plus the neutral center $(0,0)$ (tints, shades, and grays produced by mixing with white and black).
3D Biconic Gamut Envelope & Physical Tinting/Shading Curves
Mixing real paint with Titanium White (PW6) to raise its value inherently desaturates it into a pastel tint. Conversely, shading down toward Ivory Black (PBk9) collapses chroma into deep, low-saturation darks. Flat 2D gamut models treat color harmony as an infinite vertical cylinder, falsely allowing pure saturated yellows at deep shadow levels or intense saturated ultramarines at highlight values ($L > 0.85$).
This engine enforces a true 3D biconic gamut envelope anchored by physical White ($L_w = 0.965$) and physical Black ($L_k = 0.170$). For every single pixel, its exact perceptual luminance ($L$) calculates a sliced convex mixing hull interpolating between each pigment's intrinsic peak chroma point and the White/Black apexes. This prevents artificial supersaturation at tonal extremes and produces faithful, lifelike studio mixing boundaries.
Why Oklab & Strict Luminance Preservation Matter
In standard HSL or HSV color models, pigments cluster unnaturally, saturation is distorted, and changing hues alters the perceived brightness of forms.
This tool executes all conversions in Oklab (a uniform perceptual color space developed by Björn Ottosson). When pixels fall outside the physical mixing hull, their chromaticity coordinates $(a, b)$ are projected to the closest point on the hull perimeter, while their exact original perceptual luminance (\(L\)) remains 100% untouched. If a projected color falls slightly outside display sRGB boundaries at high lightness, a radial desaturation step along the exact same hue axis brings it into display gamut without ever altering luminance.
Staple Studio Palettes Included
- Zorn Palette: The legendary portrait palette of Anders Zorn: Ivory Black (PBk9 acting as a cool blue), Cadmium Red / Vermilion (PR108), Yellow Ochre (PY43), and Titanium White (PW6).
- Split Primary (Warm & Cool): 6-tube powerhouse with warm and cool pairs of Yellow, Red, and Blue. Gives wide chromatic versatility without gamut muddiness.
- Earth Plein Air: The landscape staple with Raw Umber, Burnt Sienna, Yellow Ochre, Viridian, and Ultramarine Blue for rich, naturalistic foliage, rock, and earth tones.
- Modern CMY Primary: Cyan (Phthalo Blue), Magenta (Quinacridone), and Cadmium Yellow for ultra-clean, high-chroma high-key mixing.