Duotone Image

How Duotone Image works

Map shadows and highlights to two colours of your choice. Duotone replaces luminance with a gradient between two chosen colours. 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.

Two colours and a luminance ramp

The image is reduced to luminance, then every pixel is mapped between two chosen colours: shadow colour at luminance 0, highlight colour at 255, linear interpolation in between.

That is genuinely how a duotone print works — two inks, one carrying the darks and one the lights — which is why it looks more designed than a tint overlay.

Choosing the pair

The defaults are near-black shadows and a bright cyan highlight. A classic alternative is dark navy with warm cream, which reads as editorial print; another is deep purple with orange for a poster look.

Keep the highlight colour light and the shadow colour dark. Two mid-tones produce mud, because there is no contrast at either end of the ramp.

Practical notes

Duotone flattens detail in the midtones because the ramp is linear; a photo with a wide tonal range keeps more structure than a flat-lit one. PNG output preserves the flat colours cleanly.

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