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 in, and in what groupings. The logic is pure deduction: no guessing needed for a well-formed puzzle.

This guide walks through every technique from reading your first clue to resolving the most complex grids. Work through it in order, or jump to the level that challenges you.

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 along the left side — numbers indicating consecutive filled groups in that row, left to right.
Column clues along the top — same format, top to bottom.

The rule: Fill exactly the cells specified by the clues, leaving a gap of at least one empty cell between each group in the same line.

A clue of 3 2 means: somewhere in the line, there’s a group of 3 consecutive filled cells, then a gap of at least 1 empty cell, then a group of 2 consecutive filled cells — in that order.

A clue of 0 (or an empty space) means the entire line is empty.

Cells have three states:

Filled (■) — definitely filled.
Empty (✕ or ·) — definitely not filled (marking these is crucial to avoid mistakes).
Unknown — not yet determined.

The goal: Determine the state of every cell using only the clues. When you’re done, the filled cells reveal a picture.

Reading Nonogram Clues

Before solving, understand what the clue numbers mean in terms of minimum space required.

Minimum line length for a clue: Add up all the numbers, plus one empty cell between each group.

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

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

If the line is 10 cells, there are 3 “slack” positions — the groups can slide around within those 3 extra cells.

Key insight: slack = line length − minimum length. The smaller the slack, the more cells you can determine immediately.

Beginner Techniques

The Overlap Method

The overlap method is the single most important nonogram technique. It applies whenever a clue group is large enough relative to the line to create an overlap between its leftmost and rightmost possible positions.

How it works:

For a single clue of value K in a line of length N:

Leftmost position: the group starts at cell 1 and occupies cells 1 through K.
Rightmost position: the group starts at cell (N − K + 1) and occupies cells (N − K + 1) through N.

Any cell that falls in both ranges — between cell (N − K + 1) and cell K — must be filled, regardless of where the group actually ends up.

Formula: Cells from position (N − K + 1) through K are always filled (when this range is non-empty, i.e., K > N/2).

Example: Line of 10 cells, clue 7.

Leftmost: fills cells 1–7.
Rightmost: fills cells 4–10.
Overlap: cells 4–7 must be filled. Mark them.

You haven’t placed the full group yet (it might start at 1, 2, 3, or 4), but you know cells 4–7 are filled for certain.

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

For clue 5 3 in a 12-cell line:

The 5-group leftmost: cells 1–5. Rightmost: cells 5–9 (because the 3-group needs 3+1=4 cells after it, leaving room for 5 to end at cell 9). Overlap: cell 5.
The 3-group leftmost: cells 7–9 (after the 5 + 1 gap). Rightmost: cells 10–12. Overlap: cells 10–12… wait: rightmost start of 5 = 12−5−1−3+1 = 4; rightmost of 5-group = 4 to 8. Then 3-group leftmost = 10, rightmost = 10. Overlap = cells 10–12. Actually let me recalculate.

Let me be precise. For 5 3 in a 12-cell line:

Minimum length = 5 + 1 + 3 = 9 cells. Slack = 3.
5-group: leftmost start = 1 (occupies 1–5). Rightmost start = 1 + slack = 4 (occupies 4–8). Overlap: cells (4) to (5) = cells 4 and 5.
3-group: leftmost start = 7 (occupies 7–9). Rightmost start = 7 + slack = 10 (occupies 10–12). Overlap: cells (10) to (9)… that’s empty because 10 > 9.

So in this example: fill cells 4 and 5 (from the 5-group overlap). The 3-group has no overlap. That’s still 2 certain cells from a single clue application.

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

Edge Logic

If a line’s first clue is K, and the line begins with K consecutive filled cells already marked — then the cell immediately after those K cells must be empty (it’s the mandatory gap). Mark it empty.

Similarly, if the first filled cell from the left appears at position P, the first clue group cannot end before position P — it must overlap position P.

Working from both edges inward often pins the positions of the first and last groups.

Edge logic in practice: If a row has clue 4 and you’ve already determined the first cell is filled, the group of 4 starts at or before cell 1. If the cell at position 5 is marked empty, the group must be entirely within cells 1–4 — so the group is exactly cells 1–4. Mark cells 2, 3, 4 filled, and mark cell 5 (already empty) confirmed.

Completed Lines

When you’ve placed all groups in a line and the total filled count equals the sum of the clues, the remaining cells in that line are empty. Mark them all.

This is easy to miss but gives you free information for crossing off candidates in the perpendicular direction.

Intermediate Techniques

Space Constraints

After partial solving, lines often have known filled and empty cells that constrain where remaining groups can go.

How to apply:

Look at the current state of a line: some cells filled, some empty, some unknown.
The empty cells divide the unknown regions into segments.
Check whether each segment is large enough to fit any remaining group that must go there. If a segment is too small for any remaining group, all its cells are empty — mark them.

Example: Line has clue 3 2. After overlap work, you know cell 6 is empty. That splits the line into a left segment (cells 1–5) and a right segment (cells 7–10). The 3 group needs 3 cells — fits in the left. The 2 group needs 2 cells — fits in the right. But if the left segment were only 2 cells wide, the 3 group couldn’t fit there, and you’d know the 3 is in the right and the 2 is somewhere else, or the entire setup is wrong (flagging a solving mistake).

Simple Deductions from Filled Cells

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

If two consecutive filled cells appear in a line with clue 2 2 2, each filled pair must belong to one of the three groups. If you have filled cells at positions 3–4 and 8–9, and empty cells at positions 1–2, 5–7, and 10, you can deduce which groups are placed.

Working with isolated filled cells: If a single filled cell is surrounded by known empty cells (or edges), it must belong to a group of exactly 1. If no clue in that line has a group of size 1, you have a contradiction — recheck your earlier deductions.

Advanced Strategies

Contradiction Method

The contradiction method (also called “trial and proof”) is a powerful last resort for hard nonograms.

How it works:

Pick a cell that could be either filled or empty.
Assume it’s filled. Apply all basic techniques with that assumption.
If you reach a contradiction (a line becomes impossible to satisfy), the assumption was wrong — the cell must be empty.
Symmetrically: assume the cell is empty. If that leads to a contradiction, it must be 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 forced groups overlap where they shouldn’t.

The contradiction method is especially useful when all obvious overlap and space-constraint work is exhausted and the grid still has unknown cells.

Parity / Count Checks

For each line, count the total cells that must be filled (sum of all clue numbers). Compare this to the number of already-filled cells and remaining unknowns.

If a line of 10 cells has clue 5 4, exactly 9 cells must be filled and only 1 can be empty. That means nearly every cell is filled — and the single empty cell can often be pinned down by cross-referencing the perpendicular clues.

Simulating Both Placements

For clues with small slack (1 or 2), there are only 2 or 3 possible group positions. Enumerate them:

Position A: mark which cells this requires filled and which empty.
Position B: same.
Any cell that is filled in all positions → mark filled.
Any cell that is empty in all positions → mark empty.

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

Solving a Daily Nonogram: Step-by-Step Workflow

Use this sequence on every puzzle:

Calculate slack for every row and column. Lines with zero slack are fully determined — fill them immediately.
Apply the overlap method to all rows, then all columns. Repeat (new info in rows may unlock columns and vice versa).
Apply edge logic — work from the boundaries inward using known filled/empty cells.
Mark completed lines — when a line’s total filled count matches its clue sum, empty the rest.
Apply space constraints — remove segments too small for remaining groups.
Cross-reference. For every newly marked cell (filled or empty), immediately update both the row and column.
Repeat steps 2–6 until stuck.
Contradiction method if needed.

The satisfaction of a nonogram comes from watching the image emerge from pure logic. No guessing required in a well-formed puzzle.

Frequently Asked Questions

Q: What’s the difference between a nonogram and Picross?
The same puzzle type. “Nonogram” and “Griddler” are common names in Europe; “Picross” is Nintendo’s branded name for the same format. 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, the puzzle was poorly constructed (or you’ve made an error in your deductions).

Q: What size nonogram should beginners start with?
5×5 or 10×10 puzzles are ideal starting points. The logic is the same as larger grids, but fewer cells means faster feedback as you learn.

Q: Can a nonogram be solved without guessing?
Yes — always, for a well-formed puzzle. If you feel you have to guess, a technique is being missed. The contradiction method (above) is a systematic alternative to guessing that keeps the logic pure.

Q: What do the colored nonograms (color picross) involve?
Color nonograms work like standard nonograms but with multiple colors. Each number in the clue has an associated color; groups of the same color are adjacent only if separated by a gap or a different-colored group. All the techniques above apply per-color-channel.

Q: How hard are daily nonograms?
Difficulty scales with grid size and clue complexity. Puzzmint’s daily nonograms are designed as a calm, satisfying daily ritual — solvable with the techniques in this guide, without ads or interruptions.

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.
The Overlap Method Deep Dive (cluster article — coming soon) — Worked examples on 15×15 grids.
Nonogram Tips: Edge Logic and Contradiction (cluster article — coming soon) — Advanced practice puzzles.

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