Turn your phone into a tracing tool. Prop your phone over a sheet of paper, open any reference image, fade it down over the live camera view, and draw what shows through — straight onto the page below. It's a pocket camera lucida, the optical device artists have used for centuries to trace what they see.
→ Live app: lucida.hdprajwal.dev
Everything happens on your device. Your image is never uploaded, there's no account, and there's no server. It even works offline.
- A phone or tablet with a rear camera.
- A way to hold it steady above your paper — a phone tripod/overhead arm is ideal, but a stack of books, a shelf edge, or a clamp all work fine.
- A reference image saved on the device (a photo, a drawing, a sketch — anything).
- Open lucida.hdprajwal.dev and tap Start tracing, then Enable camera (allow access when asked).
- Position your phone above a blank sheet of paper so the camera looks straight down at it.
- Tap the image button and pick your reference picture — it appears over the camera.
- Drag, pinch, and rotate the image until it sits where you want on the paper, then tap Lock so it won't shift while you draw.
- Slide the Opacity down to around 30–50% so you can see both the image and your pencil through it.
- Trace the lines you see onto the paper. That's it.
Tip: for busy photos, turn on Edge detection to get clean outlines instead of a full picture — much easier to follow.
- 📷 Live camera overlay with a big opacity slider — the heart of it.
- ✋ Move, pinch-zoom, and rotate the image, plus lock, flip, and reset so you can line it up perfectly and keep it put.
- ✏️ Edge detection turns a photo into clean line-art that's far easier to trace.
- 🎨 Filters — grayscale, contrast, brightness, and invert — to make lines pop.
- ❄️ Freeze frame holds a steady still if your setup is a little shaky.
- 🔲 Grid overlay (rule of thirds) to help with proportions.
- 📒 History — every image you trace is saved on your device and reopens exactly how you left it (position, zoom, filters and all).
- 📲 Install it like an app — add it to your home screen; it works offline and keeps the screen awake while you draw.
- Mount it steady. The less the phone moves, the easier tracing is. An overhead phone stand is worth it if you trace often.
- Light the paper evenly and keep your drawing hand from casting a shadow under the camera.
- Lock the image before you start drawing so a stray touch doesn't nudge it.
- Freeze the frame if you can't get the phone perfectly still.
- Your work lives in this browser on this device — clearing the site's data erases your history, and it won't sync between devices.
The only thing that ever touches the network is the page itself (and a web font on first load). Your reference images and your tracing history stay exclusively in this browser, on this device. Nothing is uploaded, tracked, or sent anywhere.
Lucida is a tiny, dependency-free static site — no build step, no framework. To run it locally:
python3 -m http.server 8000 -d public # then open http://localhost:8000Heads-up: the camera only works in a secure context — https:// or localhost.
Over file:// or a plain-http:// LAN address it's silently blocked by the browser, so
to test on your phone you need HTTPS (any host works — this site runs on Cloudflare
Pages).
Architecture, conventions, and how to contribute live in AGENTS.md and docs/CONTRIBUTING.md.
Released under the MIT License — free to use, modify, and distribute, including commercially, with attribution. See LICENSE for the full text.
Copyright © 2026 Prajwal HD.