Turn a picture into a
nonogram that actually solves

Why most "image to nonogram" converters hand you something unsolvable

Counting clue numbers off a grid is arithmetic — every converter does it right. The hard part is that most pictures are not nonograms. A thresholded photo is full of lone cells and single-cell holes, and a one-cell feature has nothing around it to pin it down, so the grid has several answers and no way to pick between them by logic. Print that and the person solving it hits a wall that no amount of skill gets past, because there is nothing there to deduce.

This page runs the deduction instead of assuming it: it takes the clues off your grid, hands them to the solver with the answer hidden, and checks whether the solver gets your exact picture back. Three things can come out:

• It solves. One answer, reached by row and column logic alone. This is a puzzle you can hand to someone.
• It needs a guess. Consistent, but logic runs out — the cells it cannot decide are painted grey on the answer sheet so you can see where the picture is too thin. Usually fixed by a different threshold, a bigger grid, or tidying stray cells.
• It's blank or solid. Everything landed on one side of the threshold. Move the slider or tick invert.

If you'd rather draw the picture cell by cell than start from a file, the nonogram checker is the same gate with a drawing grid in front of it. If you already have clue numbers and want to know what's wrong with them, use the nonogram solver.

The gate here is the gate that fills the book

This is not a checker written for a web page. It is the routine that decides whether a drawing becomes a published puzzle: it has to close from its clues alone and land on exactly the picture it was drawn from, or it does not ship. The build that produced this page re-ran that proof on all 110 puzzles we publish — 100 in the book and 10 in the free pack — through this page's own image pipeline: each answer picture was painted into pixels, fed in as if you had uploaded it, and had to come back cell for cell and then solve. It also has to refuse: a grid of random noise must come back "needs a guess", or the build stops. A tool that says "looks great" to everything would pass every other kind of test.

Getting a picture to solve

1. Start with high contrast. Silhouettes, logos, icons and line art work; a photograph of a face at 15×15 almost never does.
2. Go bigger before you go simpler. The same picture at 20×20 has room for features that vanish at 10×10 — but bigger grids also take longer to solve by hand.
3. Move the threshold. It is the single biggest lever: one step can turn a fringe of stray cells into a solid edge.
4. Tidy stray cells last. It removes ink with no neighbour and fills holes surrounded on three sides. It is off by default and named on the button because it changes your picture — a tool that silently edits your drawing and then congratulates you on it is the thing this page exists not to be.

Solving technique, with drawn examples, is in how to solve nonograms step by step.

Puzzles that already passed the gate