tententoon

noun  ·  a self-repeating image whose copies spiral as they shrink — in the manner of M. C. Escher's Print Gallery (1956).

from the Dutch title Prentententoonstelling — prenten (prints) + tentoonstelling (exhibition),
with the coined word sitting right where the two halves meet.
A browser tool for making the same move with your own images.

---

Same picture, two infinities

Droste — a picture inside itself, dropping straight down forever. (this one is a real photograph)	tententoon — the same recursion, bent into a spiral that still closes seamlessly.

Same rule — a copy inside a copy inside a copy. One drops straight down; the other takes the scenic route, and still arrives on time.

The idea

Nest a picture inside itself and you get the Droste effect: each copy sits squarely inside the last, shrinking by the same step, forever.

A tententoon asks one stranger question — what if each copy also turns as it shrinks? The nested frames then wind into a spiral. Straight lines bow into curves, the whole picture twists, and yet nothing tears: follow any line inward and it meets itself exactly.

The trick is a single move — take the logarithm. Shrinking-and-repeating is multiplication, and logarithms turn multiplication into addition, so "shrink, then repeat" becomes "slide over, then repeat" — a plain, evenly-spaced grid. Add rotation and that grid simply tilts; roll it back up and the tilt is a spiral. The loop is seamless because, in log-space, one full turn is just a shift by exactly one step — landing you on an identical picture.

→ The whole story — why it spirals, and why it never tears: silvio-tententoon.pgs.sh/explain.html

Where the name comes from

Escher drew Print Gallery by hand in 1956 and left a white blot at its centre — the spiral grew too tight to finish. In 2003, Hendrik Lenstra and Bart de Smit found the exact map behind it: the idealised picture contains a copy of itself rotated 157.6256° and shrunk by 22.5837×. With those two numbers, they completed the picture by computer. In 2026, 3Blue1Brown turned the whole argument into a beautifully animated video.

Make one

Drop in any photo, draw the rectangle where the next copy should sit, and flip between the two infinities — the straight Droste fall or the tententoon spiral. Export the loop as a PNG, GIF, or video. Everything runs in your browser: no upload, no account, no server.

Live: silvio-tententoon.pgs.sh

---

Run it locally

npm install      # or: bun install
npm run dev      # or: bun run dev   → open the URL Vite prints
npm run build    # → dist/
npm run preview  # serve dist/ locally

Svelte 5 (runes) + Vite. Rendering is WebGL via twgl.js with a CPU-worker fallback; exports use <canvas>.toBlob (PNG), MediaRecorder (MP4/WebM), and gifenc (GIF). No backend by design.

Credits & licence

• Print Gallery / Prentententoonstelling — M. C. Escher, 1956. Escher's works are © The M. C. Escher Company; referenced here by description and link, not reproduced.
• The mathematical completion — Bart de Smit & Hendrik Lenstra, The Mathematical Structure of Escher's Print Gallery, Notices of the AMS, 2003.
• Demo image — Droste effect by Nevit Dilmen, CC BY-SA 3.0 (see public/ATTRIBUTION.txt).
• Code — AGPLv3 or later (the sample image keeps its own CC BY-SA 3.0 licence).