Scenario Blender Lighting Rendering

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.

Establish first

Workflow

1. Compose, then lock the camera. Lighting is view dependent (Andrew). Use BL.screen_xy and BL.aim_camera_at_frame_point(head, 1/3 or 2/3, 0.62) for look room, and 80 mm for boxy products. GATE: one focal element; subject near a thirds point or a deliberate symmetry, pyramid or full frame.
2. Controlled base. For a studio: world strength 0 and a near-black rough ground (Andrew). For an EEVEE interior: pb = BL.volume_probe_for_room(inner_lo, inner_hi, cell=0.5, wall=0.2) (outer samples on the inner walls), BL.probe_report(pb, inner_lo, inner_hi), then BL.bake_probes(). For an exterior: BL.outdoor_sun_sky(..., azimuth_space="world"). GATE: probe_report flags nothing and a world-only render of a sealed interior is near black.
3. Key. Use BL.three_point, BL.motivated_interior (window + practical, cheated linked key, spot practical, rims, bounce) or BL.outdoor_sun_sky. Lights stay out of walls automatically. GATE: BL.light_report(target=head, face=head) has no flags (frontal key, key below the eye line, key smaller than the head), and a clay render (BL.clay(True)) gives internal_ratio >= 2.5.
4. Supporting lights. Add fill, rim, bounce and BL.eye_light, plus BL.shadow_caster, BL.fake_sun, BL.split_world or BL.haze as needed. Linking lives on the light OBJECT (obj.light_linking, via BL.link_light), not the Light datablock. Adjust one lamp at a time: BL.light_contributions(lights, mask, dir), or in Cycles BL.lightgroup_check(exr, mask) from one render. GATE: the key has the largest share on the subject, the world is under 10 % indoors, and each rim is motivated.
5. Measure and look. r = BL.render(base) gives PNG + EXR. Then mask = BL.mask_cryptomatte(r["exr"], names) (or BL.mask_workbench), rep = BL.analyse(r["png"], mask, exr=r["exr"]), BL.verdict(rep) and BL.value_study(...), and open the images. GATE: the verdict is empty and in the value study the subject owns a value group; otherwise darken the set, carve with spots or blockers, and link the key.
6. Color. BL.color_setup(view, look, exposure) (brightness here, never by scaling lamps) and BL.color_audit(). GATE: the audit is empty, no complementary clash is flagged, clip is at most 0.5 % outside emitters, and the linear max is intended.
7. Render settings. BL.preset_eevee(quality="final", interior=...) or BL.preset_cycles(quality="final", budget="film"). For EEVEE finals, render a Cycles preview reference (Andrew). GATE: the subject is within about 30 % of Cycles and there are no engine artifacts (critique section 7).
8. Comp. Cycles: mix = BL.lightgroup_mix(gains, exr=r["exr"]) re-grades key/fill/rim/window from the EXR in about 0.2 s (BL.set_gain, RGB gains recolor). Then BL.comp_finish(bloom=0.25, vignette=0.3, contrast=0.05, source=mix["socket"]); masks with BL.matte(tree, names); pixel sizes through BL.relative_px; passes, back to beauty and view layers are in procedures P13. GATE: re-run the verdict on the finished frame; the vignette ratio should fall.
9. Deliver with evidence: final PNG, EXR, value study, the light table, the verdict, and what was not verified.

Animation: pin the sun per location with sun_azimuth within about 30 deg (Andy). Light the wide shot and propagate it to coverage. Check shots with BL.contact_sheet and BL.sheet_stats (outliers more than 0.5 stop from the median). Keep temporal denoise on and never use ray-tracing resolution 1/16.