In an image logic grid game, the only fact you need to pick your next step is the printed clue on the current square, because that clue is the exact count of black cells inside its clipped three by three neighborhood, including the clue square itself. Every neighbor that sits inside the board contributes to the count, whether it touches the clue orthogonally or diagonally; neighbors outside the four by four board are simply clipped away. To choose your next step, you read the clue, count the black marks already placed in its neighborhood, count the unknown neighbors that could still become black, and ask whether the remaining candidates can reach the clue without exceeding it. If a clue is already forced black (a small number with all neighbors unknown) or forced white (the count is already met), you move there next. The Mosaic Puzzle tool turns this counting into an exact keyboard loop on a disclosed four by four board, runs the contradiction check for you, and scores 840 on the clean checker finish.
What a Clue Number Actually Counts
Every clue in an image logic grid is a tiny promise about the squares around it. The number is the count of black cells inside a three by three window centered on the clue, with anything outside the board clipped away. The clue cell counts toward its own clue when it is marked black, and so does every neighbor that still lies inside the four by four board, whether it touches the clue orthogonally or diagonally.
This is the self-inclusive neighborhood rule that defines the genre. Simon Tatham's maintained Mosaic documentation treats the rule as the principal reference for the puzzle, while Fill-a-Pix.net independently cross-checks the same behavior. Both sources describe the clipped three by three window as the only counting surface a solver needs to worry about, and both treat diagonal neighbors as full members of that surface, not as a separate category.
The four by four board on the Mosaic Puzzle page fixes the clues in place, so a reader can verify the rule on any cell without waiting for a random board to generate. That fixed layout is also why the contradiction logic can be exhaustively audited: every clue row and every neighbor count is known up front, and the published test fixture exercises corner, edge, and interior cells in the same run.
How Neighborhood Size Changes at the Edges
A clipped three by three window is a full nine cells only when the clue sits in the interior of the board. Once the clue moves to the edge, the window is cut down to whatever still fits. That single detail decides whether a clue is "hard" (large count, many candidates) or "tight" (small count, few candidates), and it usually dictates which square you mark next. The small counter printed at the lower-right of every square makes this difference visible in real time, because the same clue number covers different total neighborhoods in different positions.
| Clue position | Cells in the neighborhood | Includes the clue square |
|---|---|---|
| Corner | 4 | Yes |
| Non-corner edge | 6 | Yes |
| Interior | 9 | Yes |
A corner clue sees four squares: itself, two orthogonal side neighbors, and one diagonal neighbor. A non-corner edge clue sees six squares: itself, three orthogonal neighbors along the row or column, and two diagonal neighbors that still sit inside the board. An interior clue sees the full three by three window, all nine cells. On the disclosed board, every clue row is already known: the first row reads 2-3-3-2, the second row reads 3-5-4-3, the third row reads 3-4-5-3, and the fourth row reads 2-3-3-2, which lines up exactly with the corner, edge, and interior sizes above.
Because the board is fixed, you can also notice which clues are already near their maximum possible count. The interior clues 5 in the second row and 5 in the third row, for instance, leave very little room for error, because their neighborhood already contains nine candidate cells.
Step Through a 4×4 Image Logic Grid
This is the actual keyboard routine on the Mosaic Puzzle board, broken into the actions you repeat for every cell you decide on.
- Use the arrow keys to move the visible selection to a clue that is either obviously forced or obviously ruled out. A small count clue with all neighbors still unknown is usually forced black first; a clue whose neighborhood already holds enough black marks to meet its number is usually forced white first.
- Press Space to mark the current square black. Press Enter to mark it white. Pressing the same key on a square that already matches returns it to unknown; pressing the opposite key replaces the previous mark without an extra step.
- Read the small counter printed at the lower-right of every square. It shows the current black total beside the required clue, so you can see at a glance how far the neighborhood is from satisfying the clue and which neighbors still have to be filled in.
- For each clue, mentally count the black marks already inside its clipped three by three window, then count the unknown cells that could still become black. If the black count is already higher than the clue, that clue is impossible and the board will show a contradiction warning on the next validation pass.
- Move to the next clue and repeat. Sixteen actions cover the full board on the disclosed checker fixture; the small counter on each clue climbs toward its printed number as you fill in, and the rest of the board falls into place once the high-count interior clues are satisfied.
- Press the restart button to wipe all sixteen cells back to unknown, reset the cursor to the first cell, restore the score, and clear the contradiction status if any was triggered.
If you are new to this kind of counting puzzle, it helps to read the clue on the cell you are about to mark, not just on the cell you are standing on. The cell you stand on is the candidate; the cells whose clues it affects are the consequences, and the contradictions arrive when those consequences disagree with a clue that was already on the board.
Score, Contradictions, and Restart
The disclosed four by four Mosaic board starts every run at 1,000 points and loses ten points per mark action, with the score floored at zero. The clean checker solution fills all sixteen squares in sixteen marks, so the score for that exact route is 1,000 − 10 × 16 = 1,000 − 160 = 840. The exact points, along with the sixteen clue numbers and the eight checker cells, are documented in the product contract so the result is reproducible across sessions.
Validation runs after every mark. For each clue, the browser calculates the black cells already present and the unknown cells that could still become black. A contradiction is reported if the black count already exceeds the clue, or if black plus unknown can no longer reach the clue. That catches two mistakes at once: overfilling (you placed too many black cells near a clue) and overclearing (you marked too many required candidates white before revealing the solution). The contradiction appears before the board is full, so you can immediately back out the last mark instead of discovering the dead end several moves later.
Restart restores the sixteen unknown cells, the first cursor, the score, and the status. A completed best score may be stored only in the browser's own localStorage, so your highest route on this specific board travels with you between visits without being sent to a server. Double-press Escape for a shared simulated spreadsheet "boss" screen, then repeat the same gesture to return to the unchanged puzzle. The puzzle itself is implemented as a semantic CSS grid rather than a canvas, every button announces its row, column, clue, mark, and selection state to assistive technology, and no action requires a pointer, an account, or hardware access.
Related Logic Puzzles Worth Trying
If you find that clipping a window and counting neighbors is the part you enjoy, the same deduction habit powers several other keyboard-friendly puzzles on the site. LITS asks you to shade one valid tetromino per region while keeping a single connected white network. Stitches joins every neighboring region pair exactly once while still respecting row and column endpoint clues. Heyawake shades exactly one cell per room while preserving a connected white area and blocking three-room corridors. Hitori shades repeated numbers from a five by five grid while keeping black cells apart and the remaining white cells connected. Each of those takes the same next-step mindset: read the clue, count the candidates, mark, validate, and apply it to a different surface.
For readers who want a guided tour of the traps that most often derail this style of puzzle, the common mistakes guide for image logic grid games walks through the dead ends you can hit on the same four by four board, and the Mosaic product page links to Simon Tatham's Mosaic reference for a fuller treatment of the self-inclusive neighborhood rule.
For a deeper look, see Pick Your Next Step in the Multitasking Game.