Nonogram

The nonogram is a logic picture puzzle in which numbers on the edges of a grid tell the player which cells to fill in, until a hidden picture appears. It was invented in Japan in the late 1980s, independently by Non Ishida, a graphic artist who devised it as a way of lighting windows of a skyscraper, and by the puzzle writer Tetsuya Nishio. British newspapers began publishing them from about 1990, and Nintendo released a console version, Picross, in 1995. It is also known as Paint by Numbers, Griddlers and Hanjie.

How it is played

The numbers beside each row and above each column give the lengths of the runs of filled squares in that line, in order, and consecutive runs are separated by at least one empty square. For example the clue 3 1 means a run of three filled cells, then at least one gap, then a single filled cell. The solver uses these clues to work out which squares must be filled and which must stay empty, marking empty ones with a cross. A puzzle is solved when every clue is met and the picture appears, and a well-made puzzle has one unique answer reachable by logic alone.

Heritage note

Nonograms are a modern Japanese contribution to the world's puzzle tradition, standing alongside Sudoku, and they belong to a long Japanese enthusiasm for grid-based puzzle books and magazines. They have been shown to be a type of problem that computer scientists classify as hard in the general case, though human solvers enjoy them in the small and medium sizes. Their pictures range from simple icons to detailed portraits on large grids, and their popularity across continents has grown through newspapers, books and games.