How to Solve Nonograms: Rules, Line Logic and Techniques for Beginners

Here's how to solve nonograms in a nutshell: each number beside a row or above a column tells you the length of a block of filled squares in that line, in order, with at least one empty square between blocks. You solve the puzzle one line at a time, finding squares that must be filled in every possible arrangement of the blocks (and squares that must stay empty), then passing that information back and forth between rows and columns until a picture appears.

That's the whole game. This guide explains the rules, the "overlap" trick that cracks most opening moves, edge logic, gluing and spaces, two fully worked puzzles drawn as grids, a practice puzzle with the answer, and the surprising history and math behind the puzzle. You won't need any special talent, just a pencil and a bit of patience.

What a nonogram is

A nonogram is a picture logic puzzle. You start with a blank grid, a list of numbers beside each row, and a list of numbers above each column. When you're done, the filled squares form a picture: an animal, a house, a letter, anything the puzzle maker drew.

Nonograms go by a lot of names. You may have seen them called Picross, Griddlers, Paint by Numbers, Pic-a-Pix, Hanjie or Japanese puzzles. Computer scientists K. Joost Batenburg (of CWI in Amsterdam) and Walter A. Kosters (of Leiden University) describe them simply in their paper "Nonograms": the goal is to find an image on a grid of pixels that matches the row and column descriptions. Most puzzles are black and white, though color versions exist too.

Words you'll see in this guide

• Clue: the list of numbers for one row or column, such as "3 1 2."
• Block: a run of filled squares described by one number in the clue. A "3" is a block of three filled squares in a row.
• Line: a single row or column.
• Fill: shade a square because it must be part of the picture. We'll draw filled squares as ■.
• Cross (or dot): mark a square as definitely empty. We'll draw these as ·. Unknown squares are shown as ?.
• Slack: how much room a line's blocks have to slide around. We'll explain how to calculate it below.

The rules of nonograms

1. Each number is a block. A clue of "4" means one block of exactly four filled squares in that line. A clue of "2 3" means a block of two, then a block of three.
2. Blocks stay in order. For rows, the clue reads left to right. For columns, it reads top to bottom. So "2 3" in a row means the block of 2 comes before the block of 3.
3. At least one empty square separates blocks. Two blocks in the same line can never touch, or they'd be one bigger block. In black-and-white puzzles, there's always at least one empty square between them.
4. Any amount of space can come before the first block or after the last. Blocks don't have to touch the edges.
5. A "0" clue (or a blank clue) means the line is entirely empty.

The Leiden paper puts the rule neatly: the clue "2 1" in a row means that from left to right, the row has a black segment of length 2 followed by a single black pixel, with one or more white pixels between them and possibly more white pixels before and after.

Well-made nonograms have exactly one solution and can be solved by logic, without guessing. Keep that in mind; it means there's always a reason for every square.

How to solve nonograms: the core method

Every nonogram solve is the same loop, repeated until the picture is complete.

1. Do the easy lines first. Look for clues that fill the whole line (like a 10 in a 10-wide grid), clues of 0, and clues with big blocks. The Conceptis solving techniques guide says solving black-and-white puzzles always starts with the longest blocks.
2. Use overlap. For each line, figure out which squares must be filled no matter where the blocks slide. Fill those.
3. Mark the empties. When a line's blocks are all placed, cross off every other square in it. Crosses are just as useful as fills.
4. Switch direction. Every square you fill or cross in a row is new information for the column it sits in, and vice versa. Scan the other direction and repeat.
5. Use edges, gluing and spaces. Once some squares are known, apply the sharper techniques below.
6. Keep going until no line changes. In a well-made puzzle, by then every square is decided.

Researchers have a name for this approach. The Leiden team notes that most nonograms in puzzle books belong to a class that can be solved by considering the information in a single row or column at a time. In other words, the line-by-line loop above is enough for nearly every puzzle you'll buy or print.

The overlap technique, step by step

Overlap (sometimes called "simple boxes") is the most important nonogram technique. It works like this: imagine pushing all the blocks as far left as they'll go, then as far right as they'll go. Any square that's filled by the same block in both positions must be filled in the answer.

The slack shortcut

You don't need to draw both positions every time. Use this quick calculation:

1. Add up all the numbers in the clue.
2. Add one for each gap between blocks (that's the number of blocks minus 1).
3. Subtract that total from the line length. The result is the slack.
4. Any block longer than the slack gets (block length − slack) squares filled in the middle of its range.

Here's an example. A 10-square line has the clue 7. The total is 7, there are no gaps, so the slack is 10 − 7 = 3. The block is longer than 3, so 7 − 3 = 4 squares are certain. Pushed left, the block covers squares 1 to 7. Pushed right, it covers squares 4 to 10. The overlap is squares 4 to 7.

Line (10 squares)	Clue	Slack	Result after overlap
Blank	7	10 − 7 = 3	? ? ? ■ ■ ■ ■ ? ? ?
Blank	8	10 − 8 = 2	? ? ■ ■ ■ ■ ■ ■ ? ?
Blank	3 4	10 − (3 + 4 + 1) = 2	? ? ■ ? ? ? ■ ■ ? ?
Blank	2 2 2	10 − (6 + 2) = 2	Nothing yet (no block is longer than 2)
Blank	5	10 − 5 = 5	Nothing yet (5 isn't longer than 5)
Blank	10	0	Every square filled

Look at the "3 4" example. The 3-block can start at square 1 or slide right by up to 2, so it always covers square 3. The 4-block can sit at squares 5 to 8 or slide to squares 7 to 10, so it always covers squares 7 and 8. Conceptis gives the same idea in its guide: a block that's longer than half the line always paints its middle squares.

Edge logic, gluing and spaces

Overlap gets you started. These techniques finish the job once some squares are known.

Edge logic: a filled square near the wall

If a filled square sits near the start of a line, the first block must cover it, and that block can't extend past the wall. Example: a 10-square line with clue "3 1" where square 1 is filled. The 3-block must start at square 1, so squares 1 to 3 are filled and square 4 must be empty.

Clue	Before	After	Why
3 1	■ ? ? ? ? ? ? ? ? ?	■ ■ ■ · ? ? ? ? ? ?	The first block touches the wall, so it runs squares 1 to 3, then a gap.
4	? ■ ? ? ? ? ? ? ? ?	? ■ ■ ■ ? · · · · ·	The 4-block must include square 2, so it starts at square 1 or 2. Either way, squares 2 to 4 are filled, and it can't reach square 6 or beyond.
5	? ? ? ? ? ■ ? ? ? ?	· ? ? ? ? ■ ? ? ? ?	A 5-block covering square 6 can start no earlier than square 2, so square 1 is empty.

That second row is sometimes called "gluing" or "reach." A known filled square pulls its block toward it, which fixes some squares and rules out squares too far away for the block to reach.

Spaces: gaps too small to hold a block

Crossed-out squares divide a line into smaller sections. If a section is too small for any remaining block, the whole section must be empty. Example: a 10-square line with clue 3, where squares 3 and 5 are already crossed out. The sections are squares 1 and 2 (too small), square 4 (too small) and squares 6 to 10. So the 3-block must be in squares 6 to 10, and overlap within that section fills square 8.

Clue	Before	After
3	? ? · ? · ? ? ? ? ?	· · · · · ? ? ■ ? ?

Completed blocks get borders

When a block reaches its full length, the squares on either side of it must be empty. Conceptis calls this out directly: when a block is fully painted, mark the squares beside it as empty. And when every block in a line is done, cross out everything else. This sounds minor, but those crosses often trigger the next move in the crossing lines.

Matching blocks to clues

Sometimes you'll have a filled square and need to work out which block it belongs to. Ask which blocks could reach that square. If only one block could, the square belongs to it, and edge logic applies. If the square is far to the left and the line's first block is short, the square might belong to the second block. Work it out by sliding the blocks to their extremes.

Worked example 1: a 5x5 heart

Let's solve a small puzzle completely. The numbers across the top are column clues (read top to bottom), and the numbers on the left are row clues (read left to right).

Clues	2	4	4	4	2
1 1	?	?	?	?	?
5	?	?	?	?	?
5	?	?	?	?	?
3	?	?	?	?	?
1	?	?	?	?	?

Step 1: Full rows

Rows 2 and 3 both have a clue of 5 in a 5-wide grid. Fill them completely.

Step 2: Overlap in row 4

Row 4's clue is 3, so the slack is 5 − 3 = 2, and 3 − 2 = 1 square is certain: the middle one, column 3.

Step 3: Columns 1 and 5

Column 1's clue is 2, and rows 2 and 3 are already filled. That's the whole block. Cross out rows 1, 4 and 5 in column 1. Column 5 works the same way.

Step 4: Overlap in columns 2, 3 and 4

Each of these has a clue of 4 in 5 squares, so the slack is 1 and 4 − 1 = 3 squares are certain: rows 2, 3 and 4. That fills row 4's columns 2 and 4. Row 4 now has its block of 3 in columns 2 to 4, which matches the clue, and its ends are already crossed.

Clues	2	4	4	4	2
1 1	·	?	?	?	·
5	■	■	■	■	■
5	■	■	■	■	■
3	·	■	■	■	·
1	·	?	?	?	·

Step 5: Row 1

Row 1's clue is "1 1," and columns 1 and 5 are crossed. That leaves only columns 2, 3 and 4 for two single blocks with a gap between them. The only way to fit them is column 2, gap, column 4. Fill columns 2 and 4, and cross column 3.

Step 6: Finish the columns

Column 2 now has rows 1 to 4 filled, which completes its block of 4, so row 5 is empty. Column 4 is the same. Column 3 has row 1 crossed and rows 2 to 4 filled, so its block of 4 must extend down to row 5. That gives row 5 its single filled square in column 3, which matches its clue of 1.

Solution	2	4	4	4	2
1 1	·	■	·	■	·
5	■	■	■	■	■
5	■	■	■	■	■
3	·	■	■	■	·
1	·	·	■	·	·

A heart. Notice that we never guessed. Each move came from one line at a time, which is exactly how most published nonograms are designed to work.

Worked example 2: a 10x10 tree

Bigger puzzles use the same moves, just more of them. Here's a 10x10 with the clues listed in two tables so they're easy to read. We checked this puzzle with a line-by-line solver, and it reaches a single picture without any guessing.

Row	1	2	3	4	5	6	7	8	9	10
Row clue	2	4	6	8	4	6	8	10	2	2

Column	1	2	3	4	5	6	7	8	9	10
Column clue	1	1 2	2 3	7	10	10	7	2 3	1 2	1

Pass 1: Rows with big blocks

• Row 8 (clue 10): fill all ten squares.
• Rows 4 and 7 (clue 8, slack 2): fill columns 3 to 8.
• Rows 3 and 6 (clue 6, slack 4): fill columns 5 and 6.
• Rows 1, 2, 5, 9 and 10 have small blocks with lots of slack, so nothing yet.

Pass 1: Columns

• Columns 5 and 6 (clue 10): fill everything.
• Columns 1 and 10 (clue 1): row 8 is filled, and that's the only block, so cross every other square.
• Columns 4 and 7 (clue 7): rows 4, 7 and 8 are filled. A single block of 7 must cover all three, so it spans at least rows 4 to 8. Fill rows 5 and 6. The block can reach up to row 2 or down to row 10, but never row 1, so cross row 1.
• Columns 3 and 8 (clue 2 3): rows 4, 7 and 8 are filled. No single block can stretch from row 4 to row 8, and the blocks must stay in order, so row 4 belongs to the 2-block and rows 7 and 8 belong to the 3-block. A 2-block that includes row 4 is either rows 3 to 4 or rows 4 to 5, so rows 1 and 2 are empty. A 3-block that includes rows 7 and 8 is either rows 6 to 8 or rows 7 to 9, so row 10 is empty.
• Columns 2 and 9 (clue 1 2): row 8 is filled. If it were the single 1-block, the 2-block would have to come after it, starting at row 10 at the earliest, and there's only one row left. So row 8 is part of the 2-block, which covers rows 7 to 8 or rows 8 to 9. Either way, row 10 is empty.

Pass 2: Back to the rows

• Row 1 (clue 2): columns 5 and 6 are filled. That's the whole block, so cross everything else.
• Row 2 (clue 4): columns 5 and 6 are filled, and columns 3 and 8 are crossed. The 4-block must sit inside columns 4 to 7, so fill columns 4 and 7 and cross the rest.
• Row 3 (clue 6): columns 1 and 10 are crossed, so the block lives in columns 2 to 9 (eight squares, slack 2). Fill columns 4 to 7.
• Rows 4 and 7 (clue 8): columns 1 and 10 are crossed, so the 8-block fills exactly columns 2 to 9.
• Row 5 (clue 4): columns 4 to 7 are already filled from the columns pass. Block complete; cross everything else.
• Rows 9 and 10 (clue 2): columns 5 and 6 are filled. Block complete; cross the rest.

Pass 2: The last columns

• Columns 2 and 9 (clue 1 2): rows 4, 7 and 8 are filled. Row 4 is the 1, and rows 7 to 8 are the 2. Everything else is empty.
• Columns 3 and 8 (clue 2 3): row 5 is now crossed (from row 5's pass), so the 2-block must be rows 3 to 4. Row 9 is crossed, so the 3-block must be rows 6 to 8.

That fills the last squares in rows 3 and 6, and the picture is done.

Solution	1	2	3	4	5	6	7	8	9	10
2	·	·	·	·	■	■	·	·	·	·
4	·	·	·	■	■	■	■	·	·	·
6	·	·	■	■	■	■	■	■	·	·
8	·	■	■	■	■	■	■	■	■	·
4	·	·	·	■	■	■	■	·	·	·
6	·	·	■	■	■	■	■	■	·	·
8	·	■	■	■	■	■	■	■	■	·
10	■	■	■	■	■	■	■	■	■	■
2	·	·	·	·	■	■	·	·	·	·
2	·	·	·	·	■	■	·	·	·	·

A pine tree with a trunk. The key moves were the full and nearly full lines (rows 4, 7 and 8, columns 5 and 6), then the crosses in columns 1 and 10, which squeezed rows 3, 4 and 7 into exact positions.

Try it yourself: an 8x8 practice puzzle

Here's a puzzle for you. It has one solution and can be solved line by line with the techniques above. The answer is below, so cover it before you start.

Row	1	2	3	4	5	6	7	8
Row clue	1 1	1 1	6	2 2 2	8	6	1 1	2 2

Column	1	2	3	4	5	6	7	8
Column clue	2	4 1	3 4	4	4	3 4	4 1	2

Hints: row 5 (clue 8) fills completely, and row 4's "2 2 2" adds up to exactly 8 with its gaps (2 + 2 + 2 + 2 = 8), so it has zero slack and you can fill it immediately, too.

Answer	1	2	3	4	5	6	7	8
1 1	·	·	■	·	·	■	·	·
1 1	·	·	■	·	·	■	·	·
6	·	■	■	■	■	■	■	·
2 2 2	■	■	·	■	■	·	■	■
8	■	■	■	■	■	■	■	■
6	·	■	■	■	■	■	■	·
1 1	·	·	■	·	·	■	·	·
2 2	·	■	■	·	·	■	■	·

It's a friendly little bug with antennae and feet.

Common nonogram mistakes

• Forgetting the gaps. When you calculate slack, add one empty square between each pair of blocks. Leaving them out makes you fill squares that aren't certain.
• Mixing up block order. The clue "1 3" means the 1 comes first (left or top). A filled square on the far left might belong to the 1, not the 3.
• Not marking empties. Crosses carry as much information as fills. Skipping them is the main reason people get stuck halfway.
• Assuming a filled square belongs to the nearest block. Check which blocks can actually reach it before applying edge logic.
• Guessing. A well-made nonogram never needs it. If you're stuck, scan every line once more; there's almost always one you skipped.
• Leaving finished lines unmarked. Conceptis recommends checking off clues once they're solved, so you don't waste time revisiting them.

The history of nonograms

Nonograms are a young puzzle compared with crosswords or mazes. The Conceptis history of Pic-a-Pix gives this timeline.

Year	Event
1987	Non Ishida, a Japanese graphics editor, wins a Tokyo competition with grid picture puzzles. Tetsuya Nishio invents the same kind of puzzle independently.
1988	Ishida publishes three picture grid puzzles as "Window Art Puzzles," and Nishio calls his version "Oekaki-Logic." The puzzles spread through Japanese magazines.
1990	James Dalgety, of The Puzzle Museum in the UK, coins the name "Nonograms" after Ishida. The Sunday Telegraph begins publishing them weekly.
1993	Ishida publishes the first book of nonograms in Japan, and The Sunday Telegraph publishes The Book of Nonograms.
1994	Dave Green, later the founder of Conceptis, encounters the puzzles in Tokyo and, with Igor Lerner, develops a computer algorithm and the name Pic-a-Pix.
1998	A Sunday Telegraph reader contest renames the puzzles "Griddlers."
2000	The first regular monthly Pic-a-Pix magazine launches in the UK, and a set of puzzles titled "Paint-by-Numbers" appears in Games World of Puzzles.

That's why the same puzzle has so many names. "Nonogram" honors Non Ishida, "Griddlers" came from newspaper readers, and "Pic-a-Pix" and "Paint by Numbers" came from publishers. Video game players may know the same format as Picross.

The math: why nonograms are hard for computers

Here's a surprising fact: solving nonograms in general is a famously hard problem for computers. In computer science terms, it's NP-complete, meaning no one knows a method that solves every possible large nonogram quickly, and finding one would settle one of the biggest open questions in math.

The Leiden researchers Batenburg and Kosters, in a short paper on automatically generating Japanese puzzles, note that the general problem is NP-hard and cite N. Ueda and T. Nagao's 1996 work, "NP-completeness results for Nonogram via parsimonious reductions." Their longer "Nonograms" paper says it was first proved there, and that it also follows from a related problem in discrete tomography, the math of rebuilding images from their projections.

So why can you solve them over breakfast? Because puzzle makers choose pictures that line logic can handle. The same Leiden paper says the nonograms in puzzle collections can usually be solved by hand, and that they belong to a special class (they call them "simple" nonograms) that can be solved one line at a time. Their generator even checks each candidate puzzle with a fast solver to make sure it doesn't need branching, the computer version of guessing.

Recent research keeps finding new angles. A 2025 paper by Aaron Foote and Danny Krizanc of Wesleyan University, "Nonogram: Complexity of Inference and Phase Transition Behavior", studies when a square can be deduced without guessing, and finds that difficulty depends largely on how dense the filled squares are. Another 2025 paper, by Maarten Löffler and colleagues, "On Solving Simple Curved Nonograms", looks at a variant drawn on curves instead of a square grid.

That density finding matches what solvers feel. Pictures with lots of long blocks give big overlaps and fall quickly. Sparse pictures full of 1s and 2s give little overlap and take far more back-and-forth.

Nonograms compared with other logic puzzles

Puzzle	What you place	What the clues tell you	Result
Nonogram	Filled or empty squares	Lengths and order of blocks in each line	A picture
Sudoku	Digits 1 to 9	Given digits	A completed number grid
Kakuro	Digits 1 to 9	Sums of runs	A completed number grid
Maze	A path	Walls and openings	A route from start to finish

Nonograms have a lot in common with sudoku's "what must be true in every case" logic, and the habit of marking what's impossible carries over directly. If you enjoy that style of thinking, our sudoku strategy guide and the roundup of games like sudoku are good next stops. If you like picture puzzles more than number puzzles, try our printable mazes or the tougher mazes for adults.

Nonograms for groups, classes and quiet time

Nonograms are a nice fit for mixed groups because they need no vocabulary and no arithmetic beyond small additions. The reward is visible, too: halfway through, a shape starts to appear, which keeps people going. The Leiden paper even notes that the mix of logic and simple integer calculation makes nonograms well suited to teaching computer science.

A few ways to use them:

• Start tiny. A 5x5 like the heart above takes a few minutes and teaches overlap, edges and crossing lines. Move to 10x10 once that feels easy.
• Solve in pairs. One person handles rows, the other handles columns, and they call out each new square. It's a great way to practice explaining reasoning.
• Theme the pictures. Hearts for February, trees for winter, a pumpkin in October. Drawing the picture first and writing the clues afterward is a lesson in itself.
• Pair with other puzzles. A nonogram plus a word search or crossword makes a balanced packet for different kinds of thinkers.

Our page on puzzles for teachers has more ideas for building puzzle time into a lesson. And if you're wondering whether puzzles actually help thinking skills, our article asking are puzzles good for the brain looks at what the research does and doesn't show.

Tips for bigger and harder nonograms

• Do a full sweep of every row, then every column. Don't hop around at random. Systematic sweeps make sure you never miss a line that just changed.
• Check the sum quickly. For any clue, add the numbers plus the gaps. If it equals the line length, the line is fully determined. If it's close, overlap will give you a lot.
• Work from the edges. Squares near the wall restrict blocks the most, so edge logic is strongest there.
• Use a ruler or a finger to keep your place. On a 20x20 or larger grid, it's easy to count one square off.
• Count with the clue in front of you. Say the block lengths out loud as you check them. It sounds silly but catches errors.
• For color nonograms, mind the color rule. Conceptis explains that blocks of different colors can touch with no gap, while blocks of the same color still need an empty square between them.
• Take breaks. Fresh eyes spot the line you skipped. That's not a cliché; it's how most stuck solvers get unstuck.

Making your own nonogram

Making a nonogram is a fun reverse puzzle. Draw a picture on graph paper, write the clue for every row and column, then erase the picture and try to solve it from the clues alone. If you get stuck and need to guess, your puzzle either has more than one solution or isn't line-solvable, so tweak the picture by adding or removing a square or two. Solid shapes with long blocks make the easiest puzzles. Thin lines and scattered dots make the hardest.

Ready for more puzzles to print? Our free puzzle maker lets you type your own words or pick a theme, choose a puzzle type, and print it with an answer key, which makes it easy to pair a nonogram session with a word search or crossword for a class, a party or a rainy afternoon. If you'd like a more number-heavy challenge next, our separate guides to kakuro and KenKen use the same patient, line-by-line style of thinking.

Five Nonogram Techniques Compared

This table compares the main line-solving techniques by what each one looks for and what it tells you.

Technique	What it looks for	What it tells you
Overlap	Squares filled by the same block when it is pushed all the way left and all the way right	A block longer than the slack always fills (block length − slack) squares in the middle
Edge logic	A filled square near the wall	The first block must cover it and can't extend past the wall, so a 3-block touching the wall fills squares 1 to 3 and square 4 is empty
Gluing, or reach	A known filled square that pulls its block toward it	Some squares become filled and squares too far away for the block to reach become empty
Spaces	Crossed-out squares that split a line into small sections	A section too small for any remaining block must be entirely empty
Borders on completed blocks	A block that has reached its full length	The squares on either side must be empty, and once every block is done the rest of the line is crossed out

Frequently Asked Questions

How do nonogram clues work?

Each number in a clue is the length of one block of filled squares in that row or column. The numbers appear in order, left to right for rows and top to bottom for columns. Between any two blocks there is at least one empty square, and there can be any number of empty squares before the first block or after the last. So a row clue of 3 1 means a block of three filled squares, then at least one gap, then a single filled square.

Where should I start on a nonogram?

Start with the lines that have the biggest blocks compared with the line length. Add the clue numbers plus one for each gap between blocks, then subtract that from the line length to get the slack. Any block longer than the slack has squares that must be filled in every arrangement. Lines with zero slack, or a clue equal to the full width, can be filled in completely right away. Then switch to the crossing lines and use what you just learned.

What is the overlap technique in nonograms?

Overlap means imagining every block pushed as far left as it can go and then as far right as it can go. Any square covered by the same block in both positions must be filled. For example, a block of 7 in a 10-square line covers squares 1 to 7 when pushed left and 4 to 10 when pushed right, so squares 4 to 7 are certain. The quick version is that a block longer than the slack fills its length minus the slack.

Should I mark empty squares in a nonogram?

Yes. Marking squares that must be empty, usually with a small x or dot, is just as important as filling squares. Empty marks split lines into smaller sections, show where blocks cannot reach, and often trigger the next deduction in the crossing line. Most solvers who get stuck halfway through a puzzle have simply stopped marking empties. Whenever a block is complete, mark the squares on both sides of it right away.

Do nonograms ever require guessing?

Well-made nonograms from puzzle books and reputable apps are designed to be solved with logic only. Research from Leiden University notes that the nonograms in puzzle collections can usually be solved one line at a time. Some computer-generated or very large puzzles may have more than one solution or need deeper reasoning that tests a possibility across several lines. If you feel forced to guess on a published puzzle, recheck your counting first, since a small error is the usual cause.

Who invented nonograms?

According to Conceptis, Non Ishida, a Japanese graphics editor, won a Tokyo competition in 1987 with grid picture puzzles, and Tetsuya Nishio invented the same kind of puzzle independently. Ishida published picture puzzles as Window Art Puzzles in 1988, and Nishio called his Oekaki-Logic. In 1990 James Dalgety of The Puzzle Museum in the UK named them nonograms after Ishida, and The Sunday Telegraph began publishing them weekly.

Are nonograms, Picross and Griddlers the same thing?

Yes, they are the same kind of puzzle under different names. Nonogram honors Non Ishida, Griddlers came from a 1998 reader contest held by The Sunday Telegraph, and Pic-a-Pix is the name used by Conceptis. Paint by Numbers and Hanjie are other common names, and Picross is the name many video game players know. The rules are the same everywhere for black-and-white puzzles, though color versions add a rule about blocks of different colors.

Why are nonograms considered hard for computers?

Solving nonograms in general is NP-complete, a result usually credited to N. Ueda and T. Nagao in 1996. That means there is no known method that quickly solves every possible large nonogram, even though small and well-designed ones are easy for people. The puzzles in books are chosen from a special class that line-by-line logic can handle, which is why you can solve them by hand while the general problem stays hard.

How do color nonograms differ from black-and-white ones?

In color nonograms, each clue number also has a color, and you fill blocks in that color. The big difference is spacing. Blocks of different colors may sit right next to each other with no gap, while blocks of the same color still need at least one empty square between them. Overlap and edge logic still work, but you track color as well as position, so it helps to work one color at a time when a line gets crowded.

Sources

We checked every source below while writing this guide. Last reviewed October 30, 2026, by Joan Ramos.

1. Pic-a-Pix History (Conceptis Puzzles)
2. Pic-a-Pix Solving Techniques (Conceptis Puzzles)
3. Nonograms (K. J. Batenburg and W. A. Kosters) (Leiden Institute of Advanced Computer Science, Leiden University)
4. Automatic Generation of Japanese Puzzles (K. J. Batenburg and W. A. Kosters, BNAIC 2008) (Leiden Institute of Advanced Computer Science, Leiden University)
5. Nonogram: Complexity of Inference and Phase Transition Behavior (Foote and Krizanc, 2025) (arXiv (Cornell University))
6. On Solving Simple Curved Nonograms (Löffler, Rote, Terziadis and Weinberger, 2025) (arXiv (Cornell University))