Alterroom

A lightweight, browser-based photo editor. The goal: apply your own Lightroom-style presets, fast, even on low-end laptops.

Edits run on the GPU using WebGL shaders, so sliders update in real time.

Features (v0.5.1)

• Library: add up to 100 photos, filmstrip with live thumbnails, each photo keeps its own edits; ← → to move between photos
• Copy and paste settings: copy one photo's look and paste it onto the selected photos or all of them (⌘/Ctrl+Shift+C / V, like Lightroom)
• Presets & LUTs: load Lightroom presets (.xmp) and colour looks (.cube 3D LUTs, with an amount slider). Settings Alterroom can't do yet are listed, not silently dropped
• Matched to Lightroom: Exposure, Contrast, White Balance and Saturation use curves measured from real Lightroom exports (85–99% of pixels match)
• Light: Exposure, Contrast, Highlights, Shadows, Whites, Blacks
• Colour: Temperature, Tint, Vibrance, Saturation
• Colour mix: Hue, Saturation and Luminance for 8 colours
• Colour grading: three-wheel view plus single Shadows, Midtones, Highlights and Global wheels, with Luminance, Blending and Balance
• Tone curve (Pro): draggable RGB / Red / Green / Blue point curves plus a 4-region parametric curve
• Edits in linear ProPhoto RGB, with halo-free Highlights and Shadows (edge-aware guided filter)
• Movable panels: drag to reorder, pop out into floating windows (move, resize, dock back), resize the sidebar. Your layout is remembered
• Beginner / Pro modes, collapsible panels, coloured slider tracks, a tip for every control
• Eye button per panel to switch its edits off; hold \ or the button to see the original
• Lightroom match meter: load a Lightroom or Camera Raw export and see how closely Alterroom matches it

Getting started

npm install
npm run dev

Then open the link Vite prints (usually http://localhost:5173).

How it works

File	What it does
src/gl/shaders.ts	GPU code: the edge-aware mask passes and the main per-pixel edit
src/gl/renderer.ts	Sets up WebGL, builds the mask once per photo, draws the preview and exports
src/gl/color.ts	Colour maths: sRGB ↔ ProPhoto matrices and Bradford white balance
src/gl/tuning.ts	Tuning knobs that control how closely each slider matches Lightroom (set by the auto-tuner)
src/gl/measured.ts	Lightroom's tone curves, measured from reference exports
src/gl/tone.ts	Turns the measured curves into lookup tables for the GPU
src/gl/curve.ts	Builds the tone curve lookup table (monotone cubic spline + parametric regions)
src/edit.ts	Every setting, its default, and the edit state (sliders, curves, LUT)
src/io/xmp.ts	Reads Lightroom .xmp presets (Camera Raw crs: settings)
src/io/cube.ts	Reads .cube 3D LUTs
src/library.ts	Photo library: file references, thumbnails, copying edits
src/accuracy.ts	Match meter: compares against a reference image using ΔE in Lab colour space
src/ui/	Panels, floating windows, saved layout, sliders, colour wheel, curve editor and control definitions
src/App.tsx	Puts it together: open, edit, before/after, export
tools/tune/	Auto-tuner: scores every slider against Lightroom exports and tunes the knobs (how to use)

Edit order: sRGB → linear ProPhoto → undo the JPEG's tone curve (scene brightness) → white balance → exposure → highlights/shadows (edge-aware) → whites/blacks → put the curve back → contrast → vibrance → saturation → sRGB → tone curve → colour mix → colour grading → LUT.

Why "undo the tone curve"? Measured against Lightroom: it treats a JPEG as if a tone curve was already applied, undoes it, multiplies for Exposure and White Balance, then puts it back without shifting hue. Copying that took Exposure from 10–42% to 85–99% match.

Highlights/Shadows use a guided filter (He et al., 2010) on a small copy of the photo's log brightness. That gives a smooth brightness map that still stops at edges, so a whole region can be brightened without glowing halos.

Measuring accuracy

Match score = % of pixels with ΔE (CIE76) below 2.3, the "just noticeable difference". Scores below are against Lightroom Classic exports of one JPEG photo (half size, sRGB, no sharpening).

Slider	Match
Exposure +1 / +2 / −1 / −2	95% / 82% / 99% / 98%
Contrast +50 / +100 / −50 / −100	97% / 88% / 98% / 92%
Temp +50 / −50	83% / 88%
Tint +50 / −50	97% / 96%
Saturation +50 / −50	96% / 99%
Whites +100 / −100	65% / 99%
Blacks +100 / −100	95% / 93%
Highlights +100 / −100	79% / 84%
Shadows +100 / −100	65% / 80%
Vibrance +100 / −100	51% / 43%

Only one test photo so far (dark and very magenta), so treat these as early numbers. See tools/tune to add more.

Roadmap

• v0.1 Load image, WebGL pipeline, 3 sliders, export
• v0.2 Screen-size preview + full-res export, Lightroom ranges, match meter
• v0.3 Linear ProPhoto, Temp/Tint, Highlights/Shadows/Whites/Blacks, Vibrance, beginner-friendly panels
• Tune every slider to 95%+ match against Lightroom exports (auto-tuner done in v0.5.1; Exposure, Contrast, Tint, Saturation, Blacks mostly there)
• v0.4 .xmp preset import, .cube LUTs, colour grading wheels, tone curve, colour mix (HSL)
• v0.5 Library of up to 100 photos, copy/paste settings
• v0.6 Batch export to a zip
• v0.7 RAW and HEIC
• v0.8 Clarity, Texture, sharpening, noise reduction, calibration, dehaze

Note

Alterroom is an independent project and isn't affiliated with Adobe. Imported presets are approximated, so results will be close to Lightroom but not identical.