# `ash-wallpaper.sh` — guide

Turns a color photo into an **Ash** wallpaper: the image is reduced to
Ash-tinted greys (dark variant), while warm *ember/gold* highlights (sunsets,
fire, lamps, skin tones) are selectively kept — the "Pleasantville" effect.

## Quick start

```sh
tools/ash-wallpaper.sh photo.jpg              # -> photo-ash.png
tools/ash-wallpaper.sh photo.jpg out.png      # custom output path
```

Requirements: ImageMagick 6.9+ or 7 (`convert` / `magick`). 4K input takes ~10s.
All knobs are environment variables read once per run — tune one, rerun,
compare.

## How it works

1. **Hue band** — the photo's HSL hue channel is thresholded: pixels with
   `hue ≤ HUE_MAX` or `hue ≥ HUE_MIN` form the "warm" band (reds, oranges,
   golds; the wrap-around at HUE_MIN catches pure crimson reds).
2. **Saturation gate** — inside that band, a saturation ramp decides how much
   of the pixel survives: nothing below `SAT_MIN`, everything from `SAT_MAX`.
   This is what keeps dull, near-grey warmish pixels as ash.
3. **Softening** — the combined mask is blurred, then re-sharpened with
   `SENSITIVITY` so highlights fade into the greys instead of showing hard
   cut-out edges.
4. **Base** — a desaturated copy is tinted along the Ash dark ramp
   (`BASE_LO` shadows → `BASE_HI` highlights, default void → chalk).
5. **Composite** — the original photo, with saturation multiplied by
   `EMBER_BOOST`, is laid over the base through the mask.

## Parameters

| Variable | Default | Meaning |
|---|---|---|
| `HUE_MAX` | `13%` | Upper edge of the warm band, in percent of the hue circle (360°). `13%` ≈ 47°, so reds, orange, ember and gold survive; yellows from ≈47° and all greens/blues fall out. |
| `HUE_MIN` | `94%` | Lower edge of the wrap-around band (`≥ 338°`). Catches deep crimson/cherry reds whose hue sits just below 360°. |
| `SAT_MIN` | `12%` | Saturation (HSL) below which a pixel becomes full grey, no matter its hue. Raise to make the image more monochrome (e.g. muted/desaturated photos: `18–25%`). |
| `SAT_MAX` | `45%` | Saturation at which the highlight is fully kept. Pastel skies/candle-lit scenes peak below 45% — lower it (`25–35%`) to let soft colour through; raise it (`55–70%`) to keep only the most saturated embers. |
| `SENSITIVITY` | `8x45%` | `-sigmoidal-contrast` applied to the mask: `contrast x midpoint`. Higher contrast → crisper, more cut-out-looking highlights; lower (e.g. `3x50%`) → dreamier, feathered bleed. The midpoint shifts the whole mask: `>50%` = only the most certain warm pixels, `<50%` = more generous. |
| `EMBER_BOOST` | `130` | Saturation multiplier (%) on the surviving pixels, so the remaining embers read against all that ash. `100` = untouched colours, `160+` = intense glow. Applied to *all* channels of those pixels, so already-saturated fire can clip — reduce if it looks neon. |
| `BASE_LO` / `BASE_HI` | `#100f12` / `#f3ede1` | Endpoints of the grey ramp (void → chalk). Any colours work, e.g. `BASE_LO=#1c1b1f BASE_HI=#e6dfd1` for a flatter panel→bone ramp. |

### Where the Ash palette sits in the hue wheel

For reference when widening/narrowing the band (hue in IM percent ≈ degrees/360):

| Colour | Hex | Hue | In band at defaults? |
|---|---|---|---|
| blood | `#c15c46` | 11° (3%) | ✅ |
| rust | `#a86a48` | 21° (6%) | ✅ |
| ember | `#e0914f` | 27° (8%) | ✅ |
| gold | `#d6b46a` | 41° (11%) | ✅ |
| pure yellow | — | 60° (17%) | ❌ (needs `HUE_MAX=17%`) |
| moss | `#8f9a5c` | 69° (19%) | ❌ |
| steel | `#7c9aa1` | 187° (52%) | ❌ |
| rot | `#b47e99` | 330° (92%) | ❌ (needs `HUE_MIN=88%` — usually you *don't* want this) |
| violet | `#a585ac` | 292° (81%) | ❌ |

## Samples

Freely-licensed photos from Wikimedia Commons, run through the script (900 px
previews). Each entry lists the exact command; the originals are shown for
comparison and credit.

### Sunset over the sea

```sh
tools/ash-wallpaper.sh sunset.jpg
```

| Original | Ash |
|---|---|
| ![sunset original](../images/samples/sunset-original.jpg) | ![sunset ash](../images/samples/ash-sunset.jpg) |

Source: [“Leigh-on-Sea beach sunset (Unsplash)”](https://commons.wikimedia.org/wiki/File:Leigh-on-Sea_beach_sunset_(Unsplash).jpg)
by Joshua Fuller, CC0.

### Campfire close-up

```sh
tools/ash-wallpaper.sh campfire.jpg
```

| Original | Ash |
|---|---|
| ![campfire original](../images/samples/campfire-original.jpg) | ![campfire ash](../images/samples/ash-campfire.jpg) |

Source: [“Closeup of raging flames in a large bonfire”](https://commons.wikimedia.org/wiki/File:Closeup_of_raging_flames_in_a_large_bonfire._-_Flickr_-_shixart1985.jpg)
by Nenad Stojkovic, [CC BY 2.0](https://creativecommons.org/licenses/by/2.0/).

### Autumn foliage

```sh
tools/ash-wallpaper.sh autumn.jpg
```

| Original | Ash |
|---|---|
| ![autumn original](../images/samples/autumn-original.jpg) | ![autumn ash](../images/samples/ash-autumn.jpg) |

Source: [“Münster, Park Sentmaring – 2015 – 9923”](https://commons.wikimedia.org/wiki/File:M%C3%BCnster,_Park_Sentmaring_--_2015_--_9923.jpg)
by Dietmar Rabich, [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/).

### City at night (ISS)

Street lamps glow soft yellow — the wide-band + soft-gate recipe from below:

```sh
HUE_MAX=17% SAT_MIN=8% SAT_MAX=60% SENSITIVITY=4x50% \
  tools/ash-wallpaper.sh city.jpg
```

| Original | Ash |
|---|---|
| ![city original](../images/samples/city-original.jpg) | ![city ash](../images/samples/ash-city.jpg) |

Source: [“Windy City of Lights (ISS070-E-105097)”](https://commons.wikimedia.org/wiki/File:Windy_City_of_Lights_(153622).jpg),
astronaut photograph, NASA/JSC Crew Earth Observations — public domain.

### Redhead portrait

Only hair and lips keep their colour; skin stays close to bone:

```sh
SAT_MIN=18% EMBER_BOOST=150 tools/ash-wallpaper.sh portrait.jpg
```

| Original | Ash |
|---|---|
| ![portrait original](../images/samples/redhead-original.jpg) | ![portrait ash](../images/samples/ash-redhead.jpg) |

Source: [“Woman redhead natural portrait 1”](https://commons.wikimedia.org/wiki/File:Woman_redhead_natural_portrait_1.jpg)
by dusdin (Flickr), cropped by Gridge, [CC BY 2.0](https://creativecommons.org/licenses/by/2.0/).

## Recipes

```sh
# Warm sunset landscape, keep the drama
tools/ash-wallpaper.sh sunset.jpg

# Night city: street lamps are soft yellow-orange, need a wider + softer gate
HUE_MAX=17% SAT_MIN=8% SAT_MAX=60% SENSITIVITY=4x50% tools/ash-wallpaper.sh city.jpg

# Portrait: only eyes/lips/warm skin glow, everything else ash
SAT_MIN=18% EMBER_BOOST=150 tools/ash-wallpaper.sh portrait.jpg

# Almost pure grey with faint traces of ember
SAT_MIN=20% SAT_MAX=70% EMBER_BOOST=100 tools/ash-wallpaper.sh photo.jpg

# Flatter, dimmer base ramp
BASE_LO=#1c1b1f BASE_HI=#e6dfd1 tools/ash-wallpaper.sh photo.jpg
```

## Batch generation

```sh
for f in ~/Pictures/vacation/*.jpg; do
  tools/ash-wallpaper.sh "$f"
done
```

## Using the results

Drop the generated files into the theme or user backgrounds folder — Omarchy
cycles through them with `Super+Ctrl+Space`:

```sh
mkdir -p ~/.config/omarchy/backgrounds/ash-dark
cp photo-ash.png ~/.config/omarchy/backgrounds/ash-dark/
```

## Troubleshooting

- **Highlights cut with hard edges** → lower the `SENSITIVITY` contrast
  (first number), e.g. `4x45%`.
- **A warm object disappears** → its hue is outside the band (check the table
  above) or its saturation is below `SAT_MIN`.
- **Grey areas look slightly tinted/brown** → those pixels are just inside the
  band; raise `SAT_MIN`.
- **Fire/embers look clipped and neon** → lower `EMBER_BOOST` towards 100.
- **Image too bright/dark after tinting** → adjust `BASE_LO`/`BASE_HI` instead
  of editing the photo.