Nonograms (or sometimes called 'Griddlers') are deceptively simple logic puzzles, starting with a blank grid as shown below. The object of the puzzle is to figure out which of the squares should be coloured in (filled in solid), and which should be left with just a dot, based on the clues given for each column and row. The resulting pattern of light and dark squares then makes up a picture, which is the solution to the puzzle.
These puzzles originated in Japan, and have been given a variety of names over the years, including picture puzzles, Japanese crosswords, or painting by numbers. You may have already seen them in puzzle magazines, or in newspapers, and there are many books of them now as well. Most paper versions of these puzzles are just two-colour, using solids and dots, because this is much easier with a single pen! However many computer-based versions use more than two colours in a picture, using coloured clues, which makes the puzzle somewhat easier.
Here at the Activity Workshop, there are several examples of these puzzles for you to try online, a puzzle solver, and of course a tutorial and worked-through example to help you get started.
They start off as a blank grid, with numbers at the edge of each row and each column, like the example picture to the right. Often the grid has a heavier style for each fifth line, as shown, which helps in counting, especially when the grid gets larger.
The numbers by each column and each row form a 'clue' to enable you to solve the puzzle.
These clues tell you how many blocks of 'solid' (or coloured-in) squares there are on
that column or row, how big they are, and in what order they appear. For example, if a row has a clue of
"4.1", this tells you that there is a block of
solid squares on this row, and to the right of it is a single block of
solid square. There must be at least one gap (ie dot) between the two blocks,
and there can be any number of dots to the left of the
4 and to the right
1. Now on its own, that doesn't seem like much of a clue, but this
row intersects each of the columns, which each have their own clues. So what you know
about the row can help you deduce things about the columns, which tell you about other
rows, and so on, until the puzzle is gradually completed.
The puzzle may have a title which can give you a clue as to what the final picture will be, but guessing with Nonograms is a bad idea. If you guess just one square wrong based on what you think the picture will look like, this quickly propagates all over the puzzle, and it is almost impossible to undo your mistake without starting all over again.
So that's a very brief introduction. If you're still not sure how to go about solving them, have a read of the tutorial for an in-depth guide. There's also a step-by-step example of solving a very simple puzzle and a practice one to try yourself. Then there's a set of ten puzzles for you to try, starting with puzzle 1.
Also, there's a special supplementary puzzle for those battling with the Mystery of the Mummy, a commercial game which includes a nonogram puzzle. Here we let you try out the puzzle in a less life-threatening environment, before you tackle the real thing.
Finally, there's an example of an automatic nonogram solver, working through a large puzzle line by line.
Can't remember which ones you've finished already? Check out your progress.
There are a handful of other related sites listed at dmoz.org.