How to Solve Nonograms (Picross): Complete Guide

Nonograms — also called Picross, Griddlers, Hanjie, or picture-cross puzzles — are logic puzzles that reveal a pixel-art image as you solve them. Each row and column has numbered clues telling you how many cells to fill and in what groups. Everything follows from logic — no guessing needed.

This guide walks through every technique from reading your first clue to completing the most complex grids.

What Is a Nonogram? Rules and Grid Basics

A nonogram puzzle has:

• A grid of cells (commonly 5×5, 10×10, 15×15, or larger).
• Row clues on the left — numbers showing the consecutive filled groups in each row, left to right.
• Column clues on top — same format, top to bottom.

The rule: Fill exactly the cells the clues specify. Between each group in a line, leave at least one empty cell as a gap.

A clue of 3 2 means: a group of 3 filled cells, then a gap of at least 1, then a group of 2 filled cells — in that order.

A clue of 0 means the whole line is empty.

Cells have three states:

• Filled (■) — definitely filled.
• Empty (✕) — definitely not filled. Always mark these to avoid mistakes.
• Unknown — not yet decided.

The goal: Use only the clues to work out the state of every cell. The filled cells reveal a picture when you are done.

Reading Clues: Minimum Space

Before solving, understand how much space each clue needs.

Minimum line length = sum of all group sizes + one gap between each group.

For clue 3 2 1: minimum = 3 + 1 + 2 + 1 + 1 = 8 cells.

If the line is exactly 8 cells, the placement is fully determined: ■■■ · ■■ · ■.

If the line is 10 cells, there are 2 extra cells of “slack” — the groups can shift around within those 2 cells.

Key insight: smaller slack = more cells you can determine immediately.

Beginner Techniques

The Overlap Method

The overlap method is the most important nonogram technique. It applies whenever a clue group is large enough relative to the line length to guarantee some filled cells regardless of exact position.

How it works:

For a single clue of value K in a line of length N (slack = N − K):

• Leftmost position: group fills cells 1 through K.
• Rightmost position: group fills cells (slack + 1) through N.
• Overlap = cells (slack + 1) through K. These cells must be filled no matter where the group ends up.

The overlap exists when K > N/2 (i.e., when the group is more than half the line length).

Example: Clue 7 in a 10-cell line.

Slack = 10 − 7 = 3. So:

• Leftmost: cells 1–7.
• Rightmost: cells 4–10.
• Overlap: cells 4–7 must always be filled.

In the full puzzle below, Row 3 has clue 7 in a 10-cell row. The diagram shows the leftmost possible position (mint), the rightmost possible position (blue), and the guaranteed overlap cells 4–7 (solid blue fill) that must be filled no matter where the group lands.

Multiple clues: Apply the overlap method to each clue group independently, accounting for the space each other group needs.

Multi-clue worked example: Clue 3 4 in a 10-cell row. Minimum space = 3 + 1 gap + 4 = 8 cells. Slack = 10 − 8 = 2.

• First group (3): Leftmost fills cells 1–3; rightmost fills cells 3–5 (both slack cells shift it right). Overlap: cell 3 must be filled.
• Second group (4): Earliest start is cell 5 (after group 1 at 1–3 and one gap); latest start is cell 7 (both slack cells push it right). Leftmost fills cells 5–8; rightmost fills cells 7–10. Overlap: cells 7–8 must be filled.

Result: mark cells 3, 7, and 8 immediately. Cells 1–2, 4–6, and 9–10 remain unknown until cross-referencing with perpendicular lines.

Tip: Apply the overlap method to every row and column before using any other technique. It often gives immediate progress across the whole puzzle.

Edge Logic

If the first clue is K and the first K cells are already filled, the cell immediately after those K cells must be empty — it is the required gap.

If a filled cell appears at position P, the first clue group must overlap position P (it cannot have ended before P). This pins the group’s range.

Work from both the left and right edges inward. This often locks the position of the first and last groups.

Worked example: Row 4 has clue 5 in a 9-cell line.

• Slack = 9 − 5 = 4. Overlap alone gives only cell 5 (C5) — just one cell determined, not very useful.
• But C1 is already filled. The group of 5 must include C1; it cannot have started after C1.
• Starting at C1 with length 5, the group must cover at least C1–C5.
• Mark C2–C5 filled (C1 was already filled). Four cells determined from one edge fact.

Notice that C1 being filled is the edge fact that pins the group — without it, only one overlap cell would be forced.

Completed Lines

When all groups in a line are placed and the total filled count equals the sum of the clues, all remaining cells in that line are empty. Mark them all — they give free information for the perpendicular direction.

Intermediate Techniques

Space Constraints

Empty cells divide a line into segments. If a segment is too small to hold any remaining clue group, all its cells are empty — mark them.

How to apply:

1. Look at the current state of a line: some cells filled, some empty, some unknown.
2. Find the empty cells — they divide the line into segments.
3. For each segment, check whether it can hold any remaining group.
4. If a segment is too small, mark all its cells empty.

Worked example: Row 8 has clue 4. Column analysis has already forced R8C1 to be empty (✕). That empty cell divides the 5-cell row into one segment: cells C2–C5 (4 cells). The remaining clue group is 4 — it fits that segment exactly and there is only one valid position. Mark R8C2, R8C3, R8C4, and R8C5 as filled.

Deductions from Filled Cells

When you have already marked some cells as filled, they constrain which group they belong to.

If two consecutive filled cells exist in a line with clue 2 2 2, each pair must belong to one of the three groups. Combining with any known empty cells often determines which group is which.

Isolated filled cells: If a single filled cell is surrounded by empty cells on both sides, it must belong to a group of exactly 1. If no clue has a group of size 1, you made an error — recheck.

Advanced Strategies

Contradiction Method

The contradiction method is a powerful technique for hard nonograms.

How it works:

1. Pick a cell that could be either filled or empty.
2. Assume it is filled. Apply all basic techniques.
3. If you reach a contradiction (a line becomes impossible to satisfy), the assumption was wrong — the cell must be empty.
4. Do the same in reverse: assume empty, check for a contradiction, conclude filled.

Contradictions to look for:

• A group’s required space no longer fits in the available unknown region.
• A line’s filled count already exceeds its clue total.
• Two groups overlap where they cannot.

Parity / Count Checks

For each line, compare the total cells that must be filled (sum of all clue numbers) against the line length. If the sum is close to the line length, almost all cells are filled — and the few empty cells can often be pinned by cross-referencing the perpendicular direction.

Simulating Both Placements

For clues with very small slack (1 or 2), enumerate all possible positions:

• Any cell that is filled in every possible position → mark filled.
• Any cell that is empty in every possible position → mark empty.

This is the generalization of the overlap method to multi-clue lines.

Solving a Daily Nonogram: Step-by-Step

1. Calculate slack for every row and column. Lines with zero slack are fully determined — fill them right away.
2. Apply the overlap method to all rows, then all columns. Repeat (new info in rows may unlock columns).
3. Apply edge logic — work from the boundaries inward.
4. Mark completed lines — when a line’s total filled count matches its clue sum, empty the rest.
5. Apply space constraints — remove segments too small for remaining groups.
6. Cross-reference: after marking any cell, update both its row and column immediately.
7. Repeat steps 2–6 until stuck.
8. Use the contradiction method if needed.

Frequently Asked Questions

Q: What is the difference between a nonogram and Picross?
The same puzzle goes by many names. “Nonogram” is an international term derived from Japanese designer Non Ishida. “Griddler” is a common generic brand name; “Picross” is Nintendo’s licensed version. The rules are identical.

Q: Do nonograms always have a unique solution?
A well-formed nonogram has exactly one solution. If you find multiple solutions, either the puzzle was poorly made or you made an error somewhere.

Q: What size should beginners start with?
5×5 or 10×10 puzzles are ideal. The logic is the same as larger grids but feedback comes faster as you learn.

Q: Can a nonogram be solved without guessing?
Yes — always, for a well-formed puzzle. If you feel you must guess, a technique is being missed. The contradiction method is a systematic, logic-only alternative.

Q: What are color nonograms?
Color nonograms use multiple colors. Each number in the clue has an associated color. Groups of the same color must be separated by a gap or a different-colored group. All the techniques above apply per color.

What to Try Next

• How to Solve Sudoku: Complete Guide — From naked singles to X-Wing, all levels covered.
• How to Solve Logic Grid Puzzles — Deduction chains and multi-category reasoning.

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