Threshold Image

How Threshold Image works

Convert an image to pure black and white with no greys. Every pixel becomes black or white depending on whether it is above the midpoint. Everything happens inside this page: the tool reads your input, runs the calculation or conversion locally, and hands the result back to you. Nothing is transmitted, because there is no backend to transmit it to.

That design choice is deliberate. Most free tool sites upload your files to a server, process them there, and quietly keep a copy. Toolcin cannot do that — the site is a set of static files. If your connection dropped the moment the page finished loading, every tool would still work.

One decision per pixel

Each pixel's luminance is computed with the perceptual weights — 0.2126 red, 0.7152 green, 0.0722 blue — and compared with 128. Above it becomes pure white, below it becomes pure black. There is no grey in the output.

Those weights matter: a bright green and a dark blue can have the same apparent brightness to a naive average but very different luminance, so the threshold lands in a different place.

Where thresholding earns its place

Preparing a scanned document for OCR, where a clean black-on-white image reads better than a grey one. Making a stencil or a screen-print separation. And turning a pencil sketch into line art.

Because the cutoff is fixed at 128, results depend entirely on the source exposure — a slightly dark scan becomes a black blob. Brighten first, then threshold.

Why it does not look like a photo filter

Thresholding discards almost all information, so it looks graphic rather than photographic. That is the point when the goal is a stamp, a logo treatment or OCR input, and a disappointment when the goal was a “black and white photo”.

Good to know

• Works offline once loaded, including on flights and in locked-down networks.
• No file size limit beyond your device's own memory.
• Free to use, with no account and no usage counter.
• Results are produced locally, so they are not logged or shared with anyone.

Questions