Black and White Image Converter

Black and white strips away colour so that light, shape and texture stand out — classic portraits, moody landscapes, cleaner product shots, or documents that print crisply. This converter offers several ways to turn colour into grey, plus a pure two-tone mode with a manual or automatic threshold for scans, signatures and stencils. It works on batches and keeps transparency, all in your browser.

How to use this tool

1. Choose one or more images.
2. Pick Grayscale for shades of grey or Pure black and white for two tones.
3. Choose the grey conversion: Rec. 709 luminance looks natural; a single colour channel gives filter effects — red darkens blue skies like a red filter on film.
4. For two tones set the threshold or tick Otsu to choose it automatically; adjust contrast if needed.
5. Download the converted images.

Formula

Grey = 0.2126 R + 0.7152 G + 0.0722 B (Rec. 709) · 0.299 R + 0.587 G + 0.114 B (Rec. 601)

The weights reflect how bright each primary looks to the eye: green most, blue least. Average uses (R + G + B) ÷ 3, lightness (max + min) ÷ 2. Contrast c (−100…100%) applies f = 259(C + 255) ÷ (255(259 − C)) with C = 2.55c around mid-grey: grey′ = f × (grey − 128) + 128. Otsu’s method tries every threshold and keeps the one that maximises the variance between the dark and light groups.

Example

A blue sky pixel of (37, 99, 235) becomes 96 with Rec. 709 (7.9 + 70.8 + 17.0 = 95.6), 96 with Rec. 601 (11.1 + 58.1 + 26.8), 124 with the average and only 37 with the red channel — which is why the red-channel option turns skies dramatically dark. With a two-tone threshold of 128 that pixel turns black.