Convert an image to grayscale online
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Convert any photo to black and white using perceptually-weighted grayscale conversion (not just a flat colour average), which produces more natural-looking results than a naive RGB average. Upload your image and download the grayscale version — entirely in your browser using the Canvas API.
Weighted conversion, not a flat average
The obvious way to convert to grey is to average the red, green, and blue values, and it produces noticeably wrong results. Human eyes are far more sensitive to green than to blue, so a flat average makes green foliage look too dark and blue skies too light. This tool uses the standard luma weighting — roughly 30 percent red, 59 percent green, 11 percent blue — which matches perceived brightness and produces a natural-looking image.
Why convert to greyscale
Beyond the aesthetic reasons, greyscale is genuinely useful for documents. Scanned text in greyscale compresses far better than the same page in colour, because colour noise across the paper disappears. It also removes the yellowish cast that scanning ageing paper produces. For photographs, greyscale can rescue an image where colour balance is badly off, since a wrong colour cast simply stops mattering.
It does not shrink the file much on its own
The image still has the same number of pixels, and each pixel still stores three identical channel values in most formats, so the file size change is modest. If your goal is a smaller file, run the greyscale result through the compressor afterwards — greyscale images compress better than colour ones, so the combination works well even though greyscale alone does little.
Frequently asked questions
- How is grayscale calculated?
- Using the Rec. 601 luma formula (0.299×R + 0.587×G + 0.114×B), which weights green more heavily since human eyes are more sensitive to it — this looks more natural than a flat average of the three channels.
- Does this reduce file size?
- Not directly — pixel count stays the same. For a smaller file too, run the result through the compress tool afterward.
- Are my images uploaded to a server?
- No, conversion happens locally in your browser using the Canvas API. Nothing is sent anywhere.
- Is this the same as desaturating in a photo editor?
- Similar in intent. This uses perceptual luma weighting, which is what most editors' greyscale conversion does, rather than a plain channel average.
- Can I get the colour back afterwards?
- No. Colour information is discarded, so keep your original if you might want it.