111 lines
5.2 KiB
Markdown
111 lines
5.2 KiB
Markdown
# `ash-wallpaper.sh` — guide
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Turns a color photo into an **Ash** wallpaper: the image is reduced to
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Ash-tinted greys, while warm *ember/gold* highlights (sunsets, fire, lamps,
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skin tones) are selectively kept — the "Pleasantville" effect.
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## Quick start
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```sh
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tools/ash-wallpaper.sh photo.jpg # -> photo-ash.png (dark base)
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PRESET=light tools/ash-wallpaper.sh photo.jpg # -> light Ash base
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```
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Requirements: ImageMagick 6.9+ or 7 (`convert` / `magick`). 4K input takes ~1s.
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All knobs are environment variables read once per run — tune one, rerun,
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compare.
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## How it works
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1. **Hue band** — the photo's HSL hue channel is thresholded: pixels with
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`hue ≤ HUE_MAX` or `hue ≥ HUE_MIN` form the "warm" band (reds, oranges,
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golds; the wrap-around at HUE_MIN catches pure crimson reds).
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2. **Saturation gate** — inside that band, a saturation ramp decides how much
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of the pixel survives: nothing below `SAT_MIN`, everything from `SAT_MAX`.
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This is what keeps dull, near-grey warmish pixels as ash.
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3. **Softening** — the combined mask is blurred, then re-sharpened with
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`SENSITIVITY` so highlights fade into the greys instead of showing hard
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cut-out edges.
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4. **Base** — a desaturated copy is tinted along the Ash grey ramp
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(`BASE_LO` shadows → `BASE_HI` highlights).
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5. **Composite** — the original photo, with saturation multiplied by
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`EMBER_BOOST`, is laid over the base through the mask.
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## Parameters
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| Variable | Default | Meaning |
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|---|---|---|
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| `PRESET` | `dark` | Grey ramp of the base. `dark` = `#100f12 → #f3ede1` (void→chalk), `light` = `#b7ae98 → #f2ecdf` (stone→paper). |
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| `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. |
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| `HUE_MIN` | `94%` | Lower edge of the wrap-around band (`≥ 338°`). Catches deep crimson/cherry reds whose hue sits just below 360°. |
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| `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%`). |
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| `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. |
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| `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. |
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| `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. |
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| `BASE_LO` / `BASE_HI` | from preset | Exact endpoints of the grey ramp. Any colour works, e.g. `BASE_LO=#1c1b1f BASE_HI=#e6dfd1` for a flatter panel→bone ramp. |
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### Where the Ash palette sits in the hue wheel
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For reference when widening/narrowing the band (hue in IM percent ≈ degrees/360):
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| Colour | Hex | Hue | In band at defaults? |
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|---|---|---|---|
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| blood | `#c15c46` | 11° (3%) | ✅ |
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| rust | `#a86a48` | 21° (6%) | ✅ |
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| ember | `#e0914f` | 27° (8%) | ✅ |
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| gold | `#d6b46a` | 41° (11%) | ✅ |
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| pure yellow | — | 60° (17%) | ❌ (needs `HUE_MAX=17%`) |
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| moss | `#8f9a5c` | 69° (19%) | ❌ |
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| steel | `#7c9aa1` | 187° (52%) | ❌ |
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| rot | `#b47e99` | 330° (92%) | ❌ (needs `HUE_MIN=88%` — usually you *don't* want this) |
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| violet | `#a585ac` | 292° (81%) | ❌ |
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## Recipes
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```sh
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# Warm sunset landscape, keep the drama (dark preset is the default)
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tools/ash-wallpaper.sh sunset.jpg
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# Night city: street lamps are soft yellow-orange, need a wider + softer gate
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HUE_MAX=17% SAT_MIN=8% SAT_MAX=60% SENSITIVITY=4x50% tools/ash-wallpaper.sh city.jpg
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# Portrait: only eyes/lips/warm skin glow, everything else ash
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SAT_MIN=18% EMBER_BOOST=150 tools/ash-wallpaper.sh portrait.jpg
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# Almost pure grey with faint traces of ember
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SAT_MIN=20% SAT_MAX=70% EMBER_BOOST=100 tools/ash-wallpaper.sh photo.jpg
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# Light-themed desktop
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PRESET=light tools/ash-wallpaper.sh beach.jpg
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```
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## Batch generation
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```sh
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for f in ~/Pictures/vacation/*.jpg; do
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tools/ash-wallpaper.sh "$f"
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done
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```
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## Using the results
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Drop the generated files into the theme or user backgrounds folder — Omarchy
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cycles through them with `Super+Ctrl+Space`:
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```sh
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mkdir -p ~/.config/omarchy/backgrounds/ash-dark
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cp photo-ash.png ~/.config/omarchy/backgrounds/ash-dark/
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```
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## Troubleshooting
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- **Highlights cut with hard edges** → lower the `SENSITIVITY` contrast
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(first number), e.g. `4x45%`.
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- **A warm object disappears** → its hue is outside the band (check the table
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above) or its saturation is below `SAT_MIN`.
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- **Grey areas look slightly tinted/brown** → those pixels are just inside the
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band; raise `SAT_MIN`.
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- **Fire/embers look clipped and neon** → lower `EMBER_BOOST` towards 100.
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- **Image too bright/dark after tinting** → adjust `BASE_LO`/`BASE_HI` instead
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of editing the photo.
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