While solving a Nonogram, every cell should be treated as one of three states: filled, empty, or unknown.
The distinction matters because an unknown cell is still available to clue blocks, while an empty cell is not. Marking empties accurately is therefore just as important as filling cells.
Filled cell
A filled cell has been proven to belong to one of the clue blocks in both the final row and final column.
VeyraPlay text examples use:
■
for a filled cell.
The visual appearance in a game may be a solid square, a colored tile, or another accessible representation. The semantic meaning is the same: the cell belongs to the final filled pattern.
You should fill a cell only when the current constraints force it.
Empty cell
An empty cell has been proven not to belong to any filled block.
VeyraPlay text examples use:
×
for a confirmed empty cell.
Many Nonogram interfaces use an X, dot, cross, or other mark. Those symbols are not different logical states. They are ways of recording the same conclusion:
this cell must remain empty.
Empty cells can:
- separate two clue blocks;
- close the edge of a completed block;
- split a line into smaller open segments;
- remove possible block placements;
- prove that another cell must be filled.
They are active information.
Unknown cell
An unknown cell has not yet been determined.
VeyraPlay text examples use:
?
for unknown.
This is a temporary solving state, not a third kind of final solution cell.
An unknown cell might eventually be filled or empty. Until a deduction proves one of those states, both possibilities must remain available if they are compatible with the clues.
Why unknown and empty must stay separate
Suppose a line contains:
??×????
The X divides the available space. No clue block can cross through that confirmed empty cell.
But if the line is:
???????
there is no such boundary. All seven cells are still potentially available.
If you mentally treat every unfilled cell as empty, you will incorrectly eliminate legal block placements.
That is one of the most common conceptual mistakes for new solvers.
A cell moves from unknown to proven
A normal logical solve changes cells in one direction:
unknown → filled
or:
unknown → empty
Once a state is proven from correct logic, it is final for the puzzle solution.
If you later need to change it, that usually means an earlier deduction or manual entry was wrong. Undoing an error is a product action; logically, the original proof was not valid.
This is why careful solvers distinguish certainty from a tentative idea.
X is a mark, not the state itself
People often say “put an X there,” but VeyraPlay separates notation from meaning.
- empty is the logical state;
- X mark is one common way to display it.
That distinction matters across platforms.
A printed puzzle may use crosses.
A mobile app may use dots or faded cells.
An accessible interface may include patterns or labels.
The underlying logic should remain identical.
How filled cells help
A confirmed filled cell tells you that at least one clue block must cover that position.
That can restrict:
- which clue the cell belongs to;
- where the block can start;
- where it can end;
- how earlier and later blocks can fit.
A single filled cell can therefore create new forced states elsewhere in the same line.
How empty cells help
A confirmed empty cell eliminates every block placement that would cross it.
That can be extremely powerful.
Imagine a 7-cell line with clue 3:
???×???
The 3-block must fit entirely on one side of the X. It cannot occupy cells from both sides.
The line has been split into two possible open segments.
With additional filled cells or clue-order information, one of those segments may become impossible, forcing the block into the other.
Completed blocks create empty boundaries
For a single-clue 7-cell line with clue 3, suppose cells 3–5 are proven filled:
??■■■??
Because the only block has already reached length 3, it cannot extend into cell 2 or cell 6.
Those adjacent cells are forced empty:
?×■■■×?
After that, every remaining cell is also empty because the only clue has been completely satisfied.
The important reasoning is not “three filled cells look complete.” It is:
- these cells are known to belong to the clue
3; - the block already has exactly three cells;
- extending it would violate the clue length.
Unknown cells can remain after useful progress
You do not need to resolve every cell in a line at once.
A state such as:
×??■■??×
can be valuable even though four cells remain unknown.
The known empty boundaries and filled cells reduce future possibilities. A crossing line may later determine one of the unknown cells and unlock the rest.
Leaving genuinely unresolved cells unknown is correct solving behavior.
How cell states interact across rows and columns
If a row proves a cell filled, the crossing column receives a filled constraint at that position.
If a column proves a cell empty, the row receives an empty constraint.
That means no cell state belongs only to the line that discovered it.
The grid is one shared constraint system.
This is why accurate marking matters so much: an incorrect state can contaminate deductions in both directions.
Common cell-state mistakes
Leaving proven empties unmarked
You lose useful boundaries and may repeatedly reconsider impossible placements.
Marking cells empty because they “look unused”
Only mark empty when the clues prove it.
Filling a cell because a block could reach it
Possible is not the same as forced. A cell is filled only when every relevant legal arrangement requires it.
Treating X marks as decorative
An X removes that cell from every legal block placement in the line.
Forgetting to propagate a new state
After changing one cell, inspect both the row and column it belongs to.
FAQ
What does an X mean in a Nonogram?
It usually means the cell is confirmed empty and cannot be part of any clue block.
Is an unmarked cell empty?
No. Unless it has been proven empty, an unmarked cell should be treated as unknown.
Do I have to mark empty cells?
The exact notation is optional, but tracking confirmed empties is one of the most useful parts of solving a Nonogram.
Can a filled cell become empty later?
Not if the original deduction was correct. Changing a proven state means you are correcting an earlier mistake.
Are there three final cell states?
No. A completed monochrome Nonogram contains filled and empty cells. Unknown exists only while the puzzle is unfinished.
Why are empty cells useful?
They block possible placements, create separators, divide lines into segments, and can force remaining blocks into narrower spaces.
What to learn next
Read Blocks, Runs, and Gaps in Nonograms to see how filled and empty states create the structures used by nearly every solving technique.