🖼️ How to solve nonograms step by step

By Miguel Arechaga

Nonograms (also called picross, hanjie or griddlers) are puzzles where you paint cells following the numbers on rows and columns... and a picture appears at the end. They look like magic, but they are solved with pure logic. Here is the method from scratch.

What the numbers mean

Each number indicates a consecutive block of painted cells in that row or column. If a 10-cell row says “4 3”, there is a block of 4 painted cells, then at least one gap, then a block of 3. The order of the numbers is the order of the blocks.

The star technique: overlap

It solves 70% of the puzzle. Imagine that 10-cell row with “7”: the block of 7 can start at the earliest in cell 1 (covering 1-7) or at the latest in cell 4 (covering 4-10). In both extremes, cells 4, 5, 6 and 7 are painted for sure: paint them now. Quick rule: if the number is greater than half the row, there is guaranteed overlap in the middle.

X marks are worth as much as paint

Mark with an X every cell you know is empty. It is not optional: X marks shorten the rows and make the next overlaps bigger. Clear cases: when a block is complete, put X on both sides; when a gap is smaller than the smallest pending block, the whole gap is X.

The row-column loop

Every cell you solve in a row is new information for its column, and vice versa. The method is a loop: sweep all rows applying overlap and X, then all columns, then start again. Each pass unlocks more than the previous one; nonograms solve in cascade.

Sacred rule: never guess

A well-made nonogram never requires guessing. If you feel stuck and tempted to try your luck, stop: there is a deduction you are not seeing (check the edges, where it usually hides). Guessing in a nonogram ends in a corrupted picture ten moves later, with no idea where you went wrong.

Final tips

• Start with rows holding big numbers or many numbers: they give the most information.
• Board edges resolve first: a block against the edge has no room for doubt.
• Start with 5×5 and 10×10 boards before jumping to the big ones.