Convert an image to greyscale
Removing colour is not one operation but several, and they give visibly different results. This tool lets you pick the weighting formula and how far to take it, from a gentle desaturation to fully neutral grey. Everything is computed pixel by pixel on your device.
How to use the Grayscale Image
- Add your colour photos.
- Leave the formula on Rec. 709 unless you want a specific look.
- Drop the strength below 100% for a partly desaturated, muted effect.
- Convert and download the greyscale versions.
Why the formula matters
Human vision is far more sensitive to green light than to red, and least sensitive of all to blue. A greyscale conversion that simply averages the three channels therefore gets the brightness relationships wrong: red objects come out too light, greens too dark, and a red rose against green leaves can lose almost all its separation. The standard fix is a weighted sum, and the weights come from broadcast standards.
| Formula | Weights (R, G, B) | Character |
|---|---|---|
| Rec. 709 | 0.2126 / 0.7152 / 0.0722 | Matches modern sRGB displays. The safe default. |
| Rec. 601 | 0.299 / 0.587 / 0.114 | The older television standard. Renders reds and skin a little lighter. |
| Average | 0.333 each | Flat and slightly muddy, but sometimes wanted for graphics. |
| Lightness | midpoint of max and min channel | Higher contrast, loses mid-tone separation. |
Strength below 100%
At 60% strength each pixel is blended 60% of the way towards its grey value, leaving a wash of the original colour. This is how the faded, low-saturation look common in editorial photography is made, and it is far more controllable than converting to grey and then tinting back.
What happens to file size
Greyscale JPGs are usually 20–40% smaller than the colour original. The reason is that the encoder stores brightness and colour separately, and in a greyscale image the two colour channels are constant, so they compress to almost nothing. Note that the output is still technically a colour file whose pixels all happen to be neutral — not a single-channel greyscale JPEG — but the size saving is real either way. PNG savings are smaller, typically 10–25%.
Practical uses
Greyscale is worth reaching for when you want a set of mismatched images to look like a set: press photos from different sources, team headshots, logos in a partner strip. It is also the quickest way to check whether a design has enough contrast to work for readers with colour vision deficiency — if two elements become indistinguishable in grey, they are relying on hue alone. Documents intended for black-and-white printing benefit too, since you can see the result before the printer decides for you.
Frequently asked questions
Which formula should I use?
Rec. 709, unless you have a reason not to. It matches how sRGB screens produce brightness, so the tonal relationships look natural.
Does greyscale make the file smaller?
Usually yes — 20–40% smaller for JPG, less for PNG — because the colour channels become constant and compress almost to nothing.
Can I make an image only partly black and white?
Yes. Lower the strength slider. At 50% the image keeps half its colour, which gives a muted, faded look.
Is transparency kept?
Yes. Only the red, green and blue channels are changed; the alpha channel is left alone, so transparent PNGs and WebPs stay transparent.
Privacy
This tool runs entirely inside your browser using WebAssembly and the Canvas/File APIs. Your files are never uploaded to ToolFlint or any third party; you can verify this in your browser's network tab or by switching to airplane mode after the page loads. Read how we process files.
Last updated 2026-09-23.