How to use the Halftone & Dot Effect Generator
- Drop in an image (or paste one). A sample still life loads first so you can see the effect straight away. Processing happens in your browser; the picture is never uploaded.
- Choose a Mode. One ink prints a single color on paper and lets you set the Screen angle, Ink, Paper and Invert. CMYK separation splits the image into cyan, magenta, yellow and black screens at the classic print angles and overlays them like inks on paper.
- Pick a Dot shape — dots, ellipses, squares, crosses or lines — and set the Cell size. The hint under the slider converts it into lines per inch for printing.
- Adjust tone. Brightness and Contrast act before screening; Dot gain fattens or thins the midtones; Black (GCR) decides how much of the dark color goes onto the black plate instead of three stacked inks.
- Download PNG for the full-resolution result, or Download SVG in One ink mode for a vector file. Show original flips back to the source for comparison.
How dots fake a continuous tone
A printing press can only put ink down or leave paper bare. To print a gray, it breaks the image into a grid of cells and puts one dot in each cell, sized so the inked fraction of the cell matches the darkness of the image there. A cell that is 30% covered reads as a light gray from normal viewing distance; one that is 90% covered reads as near black. This tool does the same: each cell samples the average tone underneath it and draws a shape whose area equals that tone.
Round dots behave in a particular way. Neighboring dots start to touch at about 78.5% coverage (π/4), and beyond that the paper shows only as small pinched gaps between them. That jump is why round-dot screens can look slightly abrupt in the dark midtones, and why printers developed elliptical dots: they join along one axis first, forming chains, and the transition is smoother. Try Ellipses on a portrait and compare the cheeks with the round-dot version.
Cell size is the other big decision. Commercial printing describes screens in lines per inch (LPI) — how many rows of cells fit in an inch. Newspapers have traditionally printed around 85 LPI and glossy magazines around 133–150 LPI, which is why you never notice the dots in a magazine. For a pop-art or comic look you want the opposite: big, visible dots.
Cell size and screen ruling
The ruling depends on the resolution you print at, so the same cell size gives a coarser screen on a 150 DPI print than on a 300 DPI one.
| Cell size | LPI at 300 DPI | LPI at 150 DPI | Typical look |
|---|---|---|---|
| 3 px | 100 | 50 | The finest setting — reads as smooth tone at arm’s length |
| 4 px | 75 | 37.5 | A little coarser than a newspaper screen |
| 6 px | 50 | 25 | Visible texture up close, good for screen printing |
| 10 px | 30 | 15 | Retro poster, dots clear at arm’s length |
| 20 px | 15 | 7.5 | Comic-panel Ben-Day style |
| 30 px | 10 | 5 | Graphic pattern, the dots are the design |
A magazine’s 150 LPI would need a 2 px cell at 300 DPI, finer than this tool goes; at that size the dots stop being an effect and become the printer’s job. A 3000-pixel-wide image at a 12 px cell gets 250 dots across, which is plenty for the image to stay recognizable. Below roughly 60 cells across, faces and lettering start to dissolve into abstract dots — sometimes exactly what you want for a poster.
Why the CMYK screens sit at 15°, 75°, 0° and 45°
When two regular grids overlap at nearly the same angle, they interfere and form a large wavy pattern called moiré. Printers avoid it by keeping the three strongest inks 30° apart: cyan at 15°, black at 45° and magenta at 75°. Yellow is the palest ink, so its own moiré is the least visible; it goes at 0°, the angle that is left over. Overlapped correctly, the four screens form small flower-like rosettes instead of waves, which you can see if you zoom into the CMYK preview.
The same logic explains the 45° default for single-ink work. The eye picks up horizontal and vertical lines most easily, so a screen tilted to 45° reads as smooth tone, while a 0° screen reads as a grid. Line screens are the exception: at 0° or 90° they look like engraving, which can be a deliberate style.
Tips from practice
Pick the cell size for the final print size. Decide how wide the print will be, multiply by the DPI, and check the dots across in the stats. Dots that look bold on screen at 1000 px wide may become fine texture once the image is printed at 18 inches.
Screen printing needs coarse screens. A common rule of thumb is a mesh count about four to five times the halftone LPI, so a 55 LPI screen wants a mesh around 230. Very small highlight dots tend to wash out of the stencil, so lift Brightness a little and let the lightest areas end in clean paper.
Use Dot gain to pre-compensate. On absorbent paper every dot spreads, and midtones print darker than on screen. A negative Dot gain value shrinks the midtone dots before printing; the slider value is how many percentage points the 50% tone moves.
Separate plates for Riso or screen work. In CMYK mode, switch off three plates under Show plates and download the remaining one — repeat for each color to get four aligned layers. For a two-color look, the Image Posterize Tool is a good way to simplify the image before screening.
Re-screening a printed scan. A photo scanned from a book already carries a dot pattern, and a new screen on top can clash with it. Choose a cell size several times larger than the original dots, or soften the scan slightly first, and the clash disappears.