Duotone effect — rebuild any photo from two colours

How to use Image Duotone

1. Choose one or more images.
2. Pick the Shadows colour. The default is a deep navy, #1e1b4b.
3. Pick the Highlights colour. The default is amber, #fbbf24.
4. Choose Save as and Quality, then press Apply.

What it does and when to use it

Duotone is a printing idea: two inks make a whole picture. On screens it has become a popular look for posters, album art, event banners, blog headers and team photo pages. It hides the differences between photos taken in different light, and it puts your colours front and centre.

It works best on photos with clear light and shade, such as portraits with side light, city skylines or sports shots. Flat, evenly lit photos give a weak result; raising Image Contrast first helps. For a plain black-and-white version instead, use Image Grayscale. For only two flat tones with no blending, use Image Threshold.

How it works

For each pixel the tool first finds its brightness with the Rec. 709 weights:

luma = (0.2126 × R + 0.7152 × G + 0.0722 × B) ÷ 255, from 0 to 1

Then each output channel is placed on the line between the two colours:

output = shadow + (highlight − shadow) × luma

So a black pixel becomes exactly the shadow colour, a white pixel exactly the highlight colour, and everything else falls in between. Transparency is kept. The processing runs in a background worker on your device and nothing is uploaded.

Worked examples

These values come from the tool’s own formula, with the default navy (30, 27, 75) and amber (251, 191, 36).

• Black (0, 0, 0) becomes the navy itself, (30, 27, 75). White becomes the amber, (251, 191, 36).
• Middle grey (128, 128, 128). Luma is about 0.5, so it lands halfway: (141, 109, 55), a muted gold-brown.
• A sky-blue pixel (100, 150, 200). Its luma is 143 out of 255, so it becomes (154, 119, 53), a little lighter than the grey.
• Black and pink (#000000 and #ff4fa3). Middle grey becomes (128, 40, 82), a deep raspberry, and white becomes the full pink.

Limits and tips

• Different colours of equal brightness merge, so detail that depends on colour alone can disappear.
• A large difference in lightness between your two colours keeps the most detail.
• PNG keeps smooth gradients cleanest; JPEG at high quality is fine for photos.