Hue shifting
Hue shifting means changing the hue, not only the brightness, as a colour ramp goes from shadow to light. It is a large part of why good pixel art looks rich instead of grey.
What it is
The simplest way to shade is to take a base colour and make it darker for shadow and lighter for light. The result works, but it looks flat and a little dirty, because darkening alone drifts towards grey and black.
Hue shifting moves the hue along the ramp as well. A typical ramp for a red cloak goes from a dark, slightly purple red in shadow, through the base red, to a warm orange-red in the light. Each step changes brightness, saturation and hue together.
Why artists do it
- It matches how light behaves. Lit areas take on the colour of the light, which is often warm. Shadows are often filled by bluish sky light.
- It keeps colour alive in shadow. A shadow that shifts hue still reads as coloured, not muddy.
- It ties a palette together. If every ramp shifts the same way, all materials look lit by the same light, and the palette feels like one set.
- It saves colours. Ramps that shift hue can share their darkest or lightest colours, so a small palette covers more materials.
Common mistakes
- Shifting too far. A ramp that runs from purple to yellow no longer reads as one material.
- Shifting the wrong way for the scene. Warm shadows and cold highlights look odd unless the lighting justifies it.
- Keeping saturation flat. Mid tones are usually the most saturated; the darkest and lightest steps often drop a little.
- Shifting each material differently. If the armour shadows go blue and the skin shadows go green, the sprite looks lit by two suns.
How to do it by hand
- Pick a base colour for the material.
- For each step darker, lower brightness, move the hue a few degrees towards your shadow colour (often blue or purple), and adjust saturation.
- For each step lighter, raise brightness and move the hue towards your light colour (often yellow).
- Look at the ramp as a strip. It should read as a smooth curve, not a jump.
- Use the same direction of shift for every material in the scene.
How Pixor does it
Pixor builds a hue-shifted ramp for each material from the model’s own colours, and you can set how far the hue shifts, from none to strong. If you would rather use fixed colours, a built-in palette, a Lospec .hex or GIMP .gpl file, or a palette taken from a picture can replace the automatic one. The ramp step is a node in the Style graph.
Related
- Palette ramps
- Selout: outlines that use ramp colours
- Palettes and the settings manual
Questions
Which way should the hue shift?
A common choice is shadows towards blue or purple and lights towards yellow or orange. The light source decides; a green-lit cave or a red sunset shifts differently.
How much should I shift?
Usually a few degrees per step. Too much and a material stops looking like one colour.