How to turn a photo black and white — the three methods compared

Turning a colour picture grey sounds like one operation, but there are several ways to decide how grey each colour becomes, and they give visibly different results. A red dress can come out almost black or a pleasant mid-grey depending on the method.

Three ways to convert

The Black and White Image Converter offers three:

• Natural weights the colour channels the way the eye judges brightness — roughly 21% red, 72% green and 7% blue, the Rec. 709 standard. Colours that look equally bright stay equally bright in grey. This is the right choice for most photographs.
• Flat takes a plain average of red, green and blue. It is the naive method: reds tend to look darker and greens lighter than they appeared. Occasionally that is the effect you want.
• High contrast applies the natural weighting, then pushes tones away from mid-grey, deepening blacks and brightening whites. It makes photographed or scanned text much easier to read, at the cost of subtle detail in a photograph.

Convert step by step

1. Add the picture.
2. Pick a method — Natural for photos, High contrast for documents.
3. Compare the result with the original shown above it.
4. Download the PNG.

The conversion runs in your browser; the picture is not uploaded.

Why reds go dark

The eye is much less sensitive to red than to green, so a pure red has little brightness and becomes a dark grey under the natural method. That is accurate to how bright it looks, but it can surprise you with red logos, lipstick or traffic signs. Flat mode lightens red, at the cost of accuracy elsewhere.

Black and white for documents

For a photo of a printed page, a receipt or a whiteboard, High contrast turns a grey, shadowy image into dark text on a clean background. It is a quick improvement before sending a photographed document, or before reading the text out with OCR. For whole PDF documents, use Convert PDF to Grayscale instead.

Black and white for design checks

Converting a design to grey is a fast test of whether it relies on colour alone: if two important elements become the same grey, people who cannot see that colour difference — or who print in black and white — lose the distinction. For a fuller check, the Colour Blindness Simulator shows the main types of colour vision deficiency.

Things to know

• Keep the original. Colour information is discarded and cannot be recovered from the grey version.
• File size barely changes. The result still has three colour channels with equal values. To share a photo, convert the PNG to JPG for a smaller file.
• Greyscale is not pure black and white. It keeps every shade of grey. A two-tone image, with only black and white, is a different effect.