# Color grading — grade blocks and LUTs

Use `grade` when you need the actual HyperFrames `data-color-grading` value to paste onto an `<img>` or `<video>`. Core presets and params-backed library looks resolve locally; future CDN-backed library looks require network unless already frozen:

**Never `cat`/read a `.cube` file into context.** A 3D LUT is ~size^3 lines of raw numbers (33^3 ≈ 36k lines at the default size). It bloats context and carries zero human/agent-legible signal. To understand or choose a LUT, use `hyperframes grade-compare` to see it rendered, or `cube-validate.mjs` for a one-line `{ok,size}` check. Read `.media/index.md` or `luts/index.json` for the description. Never read the LUT body itself.

```bash
node <SKILL_DIR>/scripts/resolve.mjs --type grade --intent "warm daylight" --project . --json
```

Preset-first output uses the core runtime vocabulary and does not freeze a file:

```json
{
  "preset": "warm-daylight",
  "intensity": 1
}
```

Paste it as an attribute value after JSON string escaping:

```html
<video
  class="clip"
  src="./media/scene.mp4"
  data-color-grading='{"preset":"warm-daylight","intensity":1}'
></video>
```

Looks beyond the preset vocabulary freeze a validated `.cube` under `.media/luts/` and return a block that references it:

```bash
node <SKILL_DIR>/scripts/resolve.mjs --type grade --intent "teal orange blockbuster" --project . --json
```

```json
{
  "intensity": 1,
  "lut": { "src": ".media/luts/grade_001.cube", "intensity": 0.85 }
}
```

Use `lut` when you only need the reusable `.cube` file:

```bash
node <SKILL_DIR>/scripts/resolve.mjs --type lut --intent "teal orange blockbuster" --project .
```

For a describable technical look, author an explicit parametric LUT with `--params`:

```bash
node <SKILL_DIR>/scripts/resolve.mjs --type lut --params '{"contrast":0.2,"temperature":-0.3}' --project .
node <SKILL_DIR>/scripts/resolve.mjs --type grade --params '{"exposure":0.2}' --project . --json
```

For a LUT generated by your own script, ingest it with `--from`; media-use validates it before registration and rejects invalid or oversized cubes:

```bash
node <SKILL_DIR>/scripts/resolve.mjs --type lut --from custom.cube --project .
```

Parametric math (`buildCube`) cannot reproduce real film stocks or emulsion looks. Use a CDN-backed scanned `.cube` entry or ingest a real scanned `.cube` for those.

For visual selection, list reusable looks with `resolve --type grade --candidates`, write the promising entries to a `grades.json`, run `hyperframes grade-compare --for <frame> --grades grades.json`, then commit the winner with `resolve -t grade` as the final `data-color-grading` block.

Smart grade is `grade --for <media>`. It runs local `ffmpeg`/`ffprobe` signalstats, merges a bounded `adjust` suggestion into the returned block, and prints the measured evidence to stderr. Stdout remains valid JSON under `--json`; the suggestion is a starting point for the agent to tune, not an automatic neutralization of intentional color.

```bash
node <SKILL_DIR>/scripts/resolve.mjs --type grade --intent "warm cinematic" --for ./frame.png --project . --json
```

Library looks live in `luts/index.json`. Each entry keeps `id`, `description`, `tags`, and `intensity`, then supplies either compact `params` for on-demand `buildCube(params)` generation or a direct CDN `url` for future scanned `.cube` files. Do not commit generated `.cube` bodies; resolve validates generated or downloaded cubes as it freezes them under `.media/luts/`.

```bash
node skills/media-use/scripts/resolve.mjs --type lut --intent "teal orange blockbuster" --project . --json
node skills/media-use/scripts/lib/cube-validate.mjs .media/luts/lut_001.cube
```