Numbers along the edges spell out runs of filled cells, read them carefully, paint the grid, and a hidden picture appears.
A nonogram is a logic picture puzzle. The numbers beside each row and above each column list the lengths of consecutive filled blocks in that line, in order, with at least one gap between blocks. Use the clues from rows and columns together to deduce which cells are filled and which are empty.
There's exactly one solution and no guessing is needed. Fill every cell correctly and the grid resolves into a picture.
The nonogram was invented twice, independently, in the same year. In 1987 Non Ishida, a Japanese graphics editor, won a competition in Tokyo by making pictures on the side of a building out of skyscraper lights switched on and off — which gave her the idea of a puzzle about filling squares in a grid.
At the same time the professional puzzle setter Tetsuya Nishio arrived at the identical design and published it in a different magazine. Ishida printed three of hers in 1988 under the name Window Art Puzzles, and showed them to the British puzzle collector James Dalgety, who took on publishing them internationally.
The mechanism is a run-length encoding read backwards. The clues describe blocks of filled cells in order, and solving is the work of finding the one arrangement consistent with every row and column at once — which is why the picture only resolves at the very end.
Nonograms are grid logic puzzles where numeric run-length clues hide a picture, solvable by pure deduction. This is an original, free browser version with three sizes plus daily and practice puzzles, playable instantly with no download or sign-up.