Lighting, rendering and compositing

Expert lighting controls where the eye goes. Shape comes from gradients, the subject is separated from its surroundings by value (checked desaturated), every light has a source and a purpose, and every decision is measured on the render, not on lamp values. Work from a controlled base, change one thing at a time, and compare. If a sibling skill named here is missing from your available skills, ask the user to install it (npx skills add scenario-labs/skills --skill <name>); unattended, proceed from tool schemas and flag the gap.

REQUIRED BACKGROUND: scenario-blender-expert (execution channel, review loop, 5.2 API changes). Related: scenario-blender-texturing-shading (materials, skin SSS), scenario-blender-previs-storyboard (shot planning, cameras).

Toolkit: scripts/bx_light.py (tested on 5.2.1): rigs placed relative to subject and camera, EEVEE/Cycles presets, color setup and audit, 5.x compositor helpers, render analysis. Import: sys.path.append("<this skill>/scripts"); import bx_light as BL.

Stance (the expert delta)

• Value separation first. Andy Goralczyk separates character from background by value in almost every shot and checks it desaturated. Andrew Price: the highest-contrast area becomes the focal point whether you want it or not (the bright window beats the couch). Fix by darkening the set before brightening the subject.
• Light size and distance are the controls. Andrew: a large source reads form and hides pores, a small one reads texture and grit, so a face key is a large source, never a small bulb (unless toon or deliberately harsh). Inverse square is an attention tool: move a light closer instead of adding helpers. No key:fill ratio is a rule (Andrew: "half the key is bogus"): dim the shadow side until it reads as shadow with detail, and measure on the subject.
• Motivate, then cheat plausibly. Every light needs a source and a color from the world (Gleb Alexandrov, Lino Thomas). Andy puts the rim on the key side, because on the shadow side it reads as a bounce from nowhere. When the source is behind the subject he fakes a key into the face. Shadow casters and light linking keep cheats off the set. Gleb stops before the image "looks lit".
• EEVEE is a trench coat (Andrew). Ray tracing is off in a factory scene. World light passes through walls unless the volume probe's outer samples sit at the inner walls (Andrew; measured 0.26 leak to 0.002; 5.2.1 puts samples one spacing inside the box, so size the box from the points). Soft lights need per-light jitter (Gleb) and custom distance (measured: automatic distance loses 8 %).
• Cycles economy (Andy, Sprite Fright): 3 bounces, no caustics, no clamping, Fast GI, and bounces faked with lights. Keep sharp speculars for the eyes and hero metal only.
• Linear and wide until the end (Jacob Holiday). EXR stays linear while PNG bakes the view transform. AgX hides clipping (linear 4 displays 0.91), so read the EXR. Global brightness is exposure in the view transform, not scaled lights (keeps every ratio, including world and emissives). AgX for scenes, Khronos PBR Neutral for product color. Set the working space once (Nathan Vegdahl).
• Rebalance in comp, not by re-rendering (Wyatt, Robin). In Cycles, light groups per role (key, fill, rim, window): one render, then gains in the compositor (BL.light_groups, BL.lightgroup_mix). EEVEE has no light-group outputs: use light linking and view layers.
• Always comp, lightly (Pau Homs): bloom, vignette, then a correction, stopping before it reads as a filter. In 5.x the compositor is a node group.
• Color has three contrasts (Lino): value, saturation and hue. Keep one saturated focus hue and desaturate its complement over large areas.