What is the overlap rule in nonograms?

Compute the line's slack: width minus (sum of the blocks + one gap between each pair). If a block is longer than the slack, the cells covered in every possible placement — the middle of the block — are forced filled. A line with zero slack is completely determined by its clue.

Where do you start a nonogram?

With the longest clues. Scan every row and column for slack, paint the forced middles of long blocks first, then use marks (X for known-empty cells) to shrink lines and create new certainties in the crossing direction.

Pixel (Nonogram) Strategy: The Overlap Rule Runs Everything

Beyond the rules — the arithmetic that paints the first cells of any picture. New to Pixel? Start with how to play, then come back.

🧮Slack: the one number that matters

For any row or column, add up its clue numbers plus one gap cell between each pair of blocks. Subtract from the line's length. That difference is the line's slack — the freedom the blocks have to slide.

Slack 0: no freedom at all. The clue is the line — paint the entire row or column immediately.
Block longer than the slack: the block can slide only within the slack, so its middle cells are filled in every legal placement. Paint those — they're certain. A block of length L forces its middle L − slack cells.
Short blocks in a high-slack line: nothing forced yet. Move on; crossing lines will shrink this one.

🧪Worked example — a real DailyGrid board

From the Wednesday, October 14, 2026 Pixel (12×12):

Row 1: clue 1-1-3-1-2. Sum = 8, gaps = 4, total span = 12, width 12 → slack 0. The whole row is determined before you look at a single column: filled, empty, filled, empty, filled-filled-filled, empty, filled, empty, filled-filled. Two such gifts on one board (row 6's 3-8 is also slack 0) mean 24 cells — a sixth of the picture — fall to pure arithmetic.

Row 2: clue 3-3-3. Span = 11, slack 1. Each 3-block is longer than the slack, so each forces its middle: cells 2–3, 6–7, and 10–11 are filled no matter how the blocks slide. Paint those six, and three columns just got their first anchor cells.

From there the board ping-pongs: row certainties start columns (column 1's clue 2-3-2-2 is also slack 0 — an entire column from its clue alone), column certainties shrink rows, and every marked-empty cell reduces a crossing line's effective width — which reduces its slack — which forces new middles. The picture appears in waves, and each wave is earned.

✖️Marking empties is half the game

Complete a block, fence it. When a placed run reaches its clue length, mark the cells on both ends empty (unless they're the board edge). Those fences shrink the line for its remaining blocks.
Too-short gaps. A gap between two filled regions that's smaller than the next block it would need to hold — and can't merge with a neighbour — is empty. Mark it.
Edge logic. If a line's first clue is a 2 and cell 2 is marked empty, cell 1 must be filled and the block sits at the very edge; the mirrored rule holds at the far edge. Edges are where slack goes to die — check them whenever a line stalls.

⚠️Common mistakes

Painting a whole block from one anchor cell. A filled cell belongs to some block; until you know which and how long, only the overlap-forced cells are safe.
Not marking empties. Playing with fills only is playing with half the information — the X marks are what shrink lines.
Ignoring the picture. Late in a solve, shapes talk: a symmetric picture with an asymmetric gap usually means the gap is the mistake. Logic first, but let the image sanity-check it.

❓FAQ

What is the overlap rule?: Slack = width − (blocks + gaps). Any block longer than the slack has forced middle cells; slack 0 means the clue fully determines the line.
Where do I start?: The longest clues — lowest slack first — then alternate rows and columns as each new certainty lands.
Where are the basic rules?: In the companion guide: How to Play Pixel (Nonogram).

▶ Play today's Pixel — free

More Pixel: daily nonogram · rules & basics · puzzle archive · More daily logic puzzles