A four-by-four Mosaic board with sixteen numbered clues is solved by classifying every square as black or white until each clue exactly matches the count of black cells inside its clipped three-by-three neighborhood, including the clue cell itself and every orthogonal and diagonal neighbor that remains inside the board. The most reliable way to avoid common mistakes in an image logic grid game of this kind is to learn the three neighborhood sizes, use the keyboard marks deliberately, and read the live counter that shows current black versus required black after every action. Mistakes in these puzzles usually come from miscounting the clipped neighborhood at the edges, treating a clue as a Nonogram-style run-length, or filling black cells faster than the still-unknown candidates can possibly satisfy the remaining clues. The fix is a fixed fixture where every clue is known, every mark is auditable, and the contradiction check fires the moment the math becomes impossible. Working with a disclosed fixture also means the solver can compare their marks against the canonical checker solution that scores 840 from a starting 1,000.
How Mosaic Puzzles Fit the Image Logic Grid Category
Image logic grid games cover a family of deduction formats in which each cell of a grid receives a clue that constrains the cell's own color or contents. Mosaic puzzles, also widely known as Fill-a-Pix, place a number on every square of the board and let that number describe the count of black squares inside a clipped neighborhood centered on the clue cell. Simon Tatham's Mosaic documentation describes the self-inclusive neighborhood and the diagonal inclusion as the defining rule for the genre, and Fill-a-Pix.net independently cross-checks the same self-inclusive behavior. The puzzle differs from a Nonogram because the clue is not a run-length for a single line; it is a count for a two-dimensional patch that shrinks as the clue sits closer to the edge.
The four-by-four version used in Lizely's Mosaic Puzzle keeps the rules identical but compresses them into a sixteen-cell board where every clue is visible at a glance. That compression makes it useful for practicing the rules before tackling larger Fill-a-Pix grids, and it makes every mistake reproducible because the fixture is disclosed and never random.
Five Mistakes Solvers Make on a 4x4 Clue Grid
Even on a sixteen-cell board, the same handful of errors derail most first attempts. Watch for these patterns when reviewing your own play.
- Forgetting that the clue cell counts itself. Many solvers treat the printed number as describing only the cells around it. The clue square is the center of its own three-by-three neighborhood, so a black clue cell always contributes one to the count.
- Ignoring diagonal neighbors. The eight cells touching the clue square orthogonally and diagonally all count. A clue of 1 on an interior cell can mean a single black corner of the neighborhood, not a single orthogonal neighbor.
- Using a uniform 9-cell rule at the edges. A corner clue sees four cells, an edge clue sees six, and only an interior clue sees all nine. Subtracting too many neighbors at the edge produces an undercount.
- Reading clues as Nonogram run-lengths. Nonogram clues describe consecutive filled cells along a line; Mosaic clues describe a count inside a patch. Mixing the two conventions is the most common transfer error from related logic grid genres.
- Marking black without watching the live counter. The small count printed at the lower-right of every square shows the current black total beside the required clue. Skipping that counter turns a solvable board into an unsolvable one.
Clipped Neighborhood Sizes at Corners, Edges, and Interior
The same three-by-three window loses cells as it approaches the board edge, and the disclosed fixture shows this directly. The fixed board has four corner clues, eight edge clues, and four interior clues, and each kind sees a different total.
| Clue position | Cells in the neighborhood | Examples on the 4x4 fixture |
|---|---|---|
| Corner | 4 (clue plus two orthogonal and one diagonal) | 2 at every corner |
| Non-corner edge | 6 (clue plus three orthogonal and two diagonal) | 3 along the top, bottom, left, and right bands |
| Interior | 9 (full 3x3 window) | 4 and 5 in the four center cells |
The clue rows of the disclosed fixture read 2-3-3-2, 3-5-4-3, 3-4-5-3, and 2-3-3-2. Every 2 sits in a corner, every 3 sits on a non-corner edge, and the 4s and 5s sit in the four interior cells. Recognizing which clues are corner, edge, and interior at a glance is the first safeguard against neighborhood mistakes.
Walking Through the Sixteen-Action Checker Fixture
The disclosed fixture solves in sixteen keyboard actions and scores 840. Use this sequence to practice every mark on the way to a clean run.
- Open the Mosaic Puzzle board. Sixteen unknown squares appear with clue numbers printed on each one.
- Press the arrow keys to move the visible selection to the top-left corner. The corner shows a clue of 2.
- Press Space to mark the current square black. The lower-right counter increments to reflect the new total.
- Move along the top row with the right arrow and use Space for black, Enter for white, until every black and white cell matches the alternating checker.
- Repeat the pattern across the second, third, and fourth rows, marking each square to match the canonical solution: black at positions 0, 2, 5, 7, 8, 10, 13, and 15; white at the other eight cells.
- Press the same mark key on a square that already matches to return it to unknown, or use the other color to overwrite the previous mark if you change your mind.
- After the sixteenth mark, validation runs on every clue. The score drops from 1,000 to 840 and the board reports completion.
If the contradiction warning fires before the board is full, undo the most recent black mark with the matching key and inspect the offending clue. A contradiction means either the black count already exceeds the clue number, or there are not enough unknown cells left to ever reach it.
Reading Contradiction Warnings and Restarting Clean
Validation runs after every single mark, not only at the end of the puzzle. For each clue the browser counts the black cells already present and the unknown cells that could still become black. A contradiction is reported when the black count already exceeds the clue, or when black plus unknown can no longer reach the clue number. The first case catches overfilling: marking one cell black that pushes a clue above its target. The second case catches premature elimination: marking a required candidate white before the math can still close.
Restart restores sixteen unknown cells, the first cursor, the starting score, and the original status, so a new attempt always begins from the same disclosed state. Because the fixture never changes, a player can compare two attempts side by side and isolate exactly which mark caused the warning. A completed best score may be stored only in the browser's localStorage, so a private record of mistake-free runs persists across sessions without an account or a sign-up step.
How the 1,000-to-840 Score Reflects Mistake-Free Solving
The starting score is 1,000 and each mark action subtracts 10 from it. The clean checker fixture needs exactly sixteen actions: eight black marks and eight white marks. Working through the arithmetic, sixteen actions at a ten-point cost each gives 160 points removed from the starting 1,000, leaving a final score of 840. Any extra action, whether an overwrite, an undo, or a correction, adds another ten-point deduction, so a 17-action finish scores 830 and a 20-action finish scores 800. The score therefore acts as a direct measure of how few second-guesses the solver made on the way to the canonical answer, and the disclosed fixture makes that score reproducible across players and sessions.
Aiming for 840 is a useful training target. Hitting it means every mark was correct the first time, the contradiction check never fired, and the keyboard was used without overwriting or cycling through unknown.
Practicing on a Disclosed Fixture in Your Browser
The full Mosaic Puzzle runs in a browser tab with keyboard or pointer controls, no download, no account, and no timer. Mouse and touch users can click for black and use the context-menu gesture for white, while keyboard users keep both hands on the arrow keys and Space or Enter. Double-press Escape opens a shared simulated spreadsheet boss screen, and repeating the gesture resumes the unchanged puzzle, which keeps the disclosed fixture intact for repeated practice.
For readers who want to generalize the avoid-mistakes mindset to other deduction formats, the same self-checking approach applies in compact fixed logic games such as math-maze route planning and missing-object scanning. Both rely on a small, disclosed fixture, a contradiction check, and a deterministic score that drops the moment a mark strays from the canonical answer.