Black and White Image Converter

1. 1Add the picture.
2. 2Pick a conversion — Natural suits photographs, High contrast suits scanned text.
3. 3Compare the result against the original above it.
4. 4Download the PNG.

Natural uses the Rec. 709 luminance weighting: roughly 21% red, 72% green and 7% blue. Those proportions reflect how sensitive the eye is to each colour, so a red and a blue that look equally bright stay equally bright as greys instead of collapsing into the same tone.

Flat is the plain average of the three channels. It is the naive method, and it tends to make reds look darker and greens lighter than they appeared — occasionally that is the effect you want, which is why it is offered.

High contrast applies the natural weighting and then pushes values away from mid-grey, deepening blacks and lifting whites. That is what makes photographed or scanned text easier to read, at the cost of losing subtle detail in a photograph.

Images are decoded by the browser, redrawn on a canvas and re-encoded on your own machine. Nothing is uploaded, so there is no waiting on a queue and no copy of your photos anywhere else.

• Use Natural for photographs; it keeps colours that looked equally bright at the same grey.
• Use High contrast for photos or scans of documents to make the text stand out.
• Check red elements, which become dark greys; Flat mode lightens them if needed.
• Keep the colour original. Colour cannot be recovered from the grey version.

• How to check a design works for colour-blind people
• How to print a PDF in black and white — and save ink
• How to turn a photo black and white — the three methods compared