A pure black and white threshold with a live histogram, an automatic split point, smoothing and a transparent background option.
Made for spray-paint and airbrush stencils, laser engraving, cutting machines and tracing a design onto wood, fabric or skin. Every pixel comes out black or white (or black on clear), and the page counts the floating pieces a cut stencil would lose. It runs on your device; nothing is uploaded.
Drop or click to upload
Drag & drop or paste from clipboard
JPG, PNG, WebP, up to 25 MB
Brightness histogram
Pixels at or below this brightness turn black.
Blurs the brightness before the threshold, so speckle and ragged edges merge into cleaner shapes.
Background
Choose, drag, drop or paste a JPG, PNG or WebP up to 25 MB. The page picks a starting threshold with Otsu's method and shows the split on the histogram.
Drag the line on the histogram or the slider. Add smoothing to clean up speckle, invert if you want the light parts cut, and tick Mark islands to see what would fall out of a cut stencil.
Save a black and white PNG, or black on transparent, at full size. For a laser cutter or vinyl cutter that needs paths, send it to the vectorizer and download an SVG.
A stencil can only have two states: material or hole, ink or no ink. A threshold is the simplest honest way to get there. Each pixel's brightness is measured, compared with one number, and the pixel becomes black if it is at or below that number and white if it is above it. There is no grey, no dot pattern and no in-between pixels on the edges, so what you see is exactly what a cutter, an engraver or a craft knife will follow.
Brightness here is luminance with the Rec. 709 weights (21.26% red, 71.52% green, 7.22% blue), the same measure your eye uses, so a bright yellow counts as light and a saturated blue counts as dark. Transparent parts of a PNG are treated as white before measuring.
The chart above the slider shows how many pixels sit at each brightness from 0 on the left to 255 on the right; bar height is the square root of the count, so small peaks stay visible. A photo of a subject against a plain background usually shows two humps, one for the subject and one for the background. The best split is in the valley between them. The shaded side of the line is the side that turns black.
Auto (Otsu) finds that valley for you. Otsu's method tries every possible threshold and picks the one where the two groups of pixels are each as uniform as possible, which is the same as pushing their average brightnesses as far apart as possible, weighted by how many pixels each group holds. It is the standard starting point in image processing and it works well on any image with two clear groups. On a photo without them, such as an evenly lit landscape, no threshold is obviously right, and you are choosing which details to keep.
Cut out the black parts of a letter O and the white middle falls out, because nothing holds it to the rest of the sheet. Stencil makers call those pieces islands and join them back with thin strips called bridges. After each change the page counts the white areas that are completely surrounded by black, ignoring specks too small to matter, and tells you how many there are. Tick Mark islands in red to see where they are. To reduce them, raise smoothing, move the threshold, or add bridges by drawing thin white lines across them in the editor. If you are cutting the white parts instead, tick Invert and the same count applies.
| Use | What to download | Tips |
|---|---|---|
| Spray paint or airbrush stencil | Black on white PNG, printed and cut by hand | Smoothing of 2 to 4 px gives shapes a knife can follow. Check the island count before you cut. |
| Laser engraving | Black on white PNG at full size | Engraving software reads a one-bit raster directly: black is burned, white is skipped. Some machines expect the reverse, which is what Invert is for. |
| Laser, vinyl or craft cutting | SVG from the vectorizer | Cutters follow paths, not pixels. Use Trace it to SVG, then load the SVG in your cutter's software. |
| Tracing and transfer | Black on transparent PNG | Lay it over a photo or a template in any app to trace by hand, or print it for carbon transfer onto wood, lino or fabric. |
A threshold keeps solid shapes, which is what cutting and stencilling need. A dither also uses only two colours but fakes grey with patterns of dots; it looks good printed and is the wrong choice for a stencil, because every dot is a separate hole. The image effects page has two dithers if that is the look you want. If you want more than two tones, the posterize tool gives 3 to 16 flat tones in greyscale mode, and the black and white converter makes a full greyscale photo.
Keep going: the stencil carries over to the next tool with no re-upload.