What is a Nonogram?

Simply speaking, Nonogram (also referred to as 'Paint by numbers', 'Japanese Crosswords', 'Pick a box', 'Logic square')  is a special type of puzzle that relies on logic (the art of mathematical deductions) in order to reveal a certain picture.

In order to fill in the picture, you will have to follow the number and color hints given to you, both vertically and horizontally.

For example, a series such as  4   2   1  means that this row/column has (in the following order) 4 consecutive blocks with a red color, 2 adjacent blocks colored green, and one block colored brown. There might be one or more blank squares between the color stripes, e.g. the above example may very well mean (if designating a row) that we have 6 blank squares, then 4 red squares followed by 2 green squares, followed by 2 blank squares, then by a brown one and finally ending with yet another blank square.

You can now discuss nonograms at Nonogram Talk.

Solving techniques

A very intuitive first step is to start filling in what you're certain of. An example of that would be like having a row of 17 cells/squares, and the hint related to that row clearly states 17 red. This means for sure that the whole row is going to be made up of 17 red blocks.

Another very useful technique is to color/mark part of the stripes that one is ultimately sure of. Suppose you have a column made up of 20 blocks. And the clue given for that column is 18 green blocks. This means that we have a series of 18 green blocks in this column, and 2 empty cells. So technically, we either have 2 spaces at the top and then 18 green blocks, or 18 green cells followed by 2 empty ones, or a last scenario where we have a space, then 18 green cells followed by another space.
What can we conclude here? That the middle 16 blocks (i.e. blocks 3 to 18) are for sure greens (we can't be sure at this stage of the top or lower twin blocks until we figure out more of the puzzle), and can be filled with confidence.

During the Nonogram puzzle solving, while filling a row (or column), you might notice that one of the columns (or rows) has reached the maximum of a certain color, so you now know that no more cells of this color can be used in this specific column, and this will indirectly help you determine the solution for other rows/columns.

Keep in mind also that even determining the color of a single cell in a Nonogram can have a great impact on an entire row or column. For instance, suppose that you have a row with a simple hint of a red 11 in a row of 17 cells, and suppose that (counting from the left), the 5th block is a blank one. This will automatically mean that the stripe of 11 red blocks is now for sure on the right because it cannot fit on the left of the blank cell. So now we know that 11 out of the 12 cells on the right are red, and can therefore apply the 2nd tip we have described above, whereby we can now be certain of the color of the middle 10 out of 12 cells on the right of blank one. So technically, don't underestimate the power of one block, and always learn to combine solving techniques.

This leads us to another point, which is that, whenever the coloring of blocks in a certain row or column in a Nonogram is finished, make sure you directly fill in the rest with (X) blanks, because without you knowing, this may lead to scenarios such as the above, where a blank can help you solve much more than you expected.

Trial and error may sometime be useful. By trying to color a cell with a certain color, or by using a spacer in some place, you might be able to determine that this will lead to future contradictions that will render your puzzle unsolvable. But keep in mind that this strategy should be a last resort after you have exhausted every coloring you can be certain about, and no more logical/mathematical deductions can be inferred from the current state of the puzzle.

Finally, it is also advisable to use your artistic sense. Sometimes (but not quiet often), a Nonogram puzzle may have more than one solution, but ask yourself a question: will this other solution really reveal something looking more meaningful than the first solution? Remember, Nonogram is a picture revealing puzzle, so hints are picked in a way to reveal something meaningful, otherwise, this would have been a simple deviation of a crosswords.

A little history/background

One might think that Nonograms are very ancient puzzles. This assumption is actually false as it was in the recent year 1987 that an avid Japanese puzzler called Tetsuya Nishio came up with this wonderful puzzle.

This quickly spread in Japan, mainly in newspapers, and then quickly was adopted on the famous Gameboy console by Nintendo.

It is also to be noted that Tetsuya has written a book about Nonograms, 6 years after this invention.