Convert Image to Grayscale Online

Convert colour images to black and white grayscale online. Free, browser-based, no upload.

Processed entirely in your browser — never leaves your device

No software needed — works in any modern browser

Fast — most operations complete in under a second

Files up to 100MB supported

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✅Processed entirely in your browser. Your file never leaves your device — no upload, no server, complete privacy.

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Converting an image to grayscale removes all colour information and represents every pixel as a shade of grey from black (0) to white (255). The conversion uses the luminance formula: grey = 0.299×R + 0.587×G + 0.114×B, which approximates how the human eye perceives brightness across colours. Grayscale is widely used in photography, document processing, and machine learning pipelines. The conversion runs entirely in your browser.

How to use

Click 'Choose Image' and select the colour image you want to convert.
Click 'Convert to Grayscale' and wait while the image is processed.
Download the grayscale image.

FAQ

What algorithm is used for the grayscale conversion?

The tool uses the ITU-R BT.601 luminance formula: grey = 0.299×R + 0.587×G + 0.114×B. This formula weights green most heavily because the human eye is most sensitive to green light, followed by red and then blue. This produces a more natural-looking grayscale than a simple average of R, G, B.

Is the grayscale image still a colour format (RGB)?

Yes. The output file is still a standard RGB or RGBA image (JPEG, PNG, or WebP), just with equal R, G, and B values for every pixel. It is not stored as a single-channel grayscale image. This ensures maximum compatibility with all applications.

Will transparency be preserved for PNG images?

Yes. The alpha channel (transparency) is preserved during grayscale conversion for PNG and WebP images. Only the R, G, B channels are modified.

Can I convert a grayscale image back to colour?

No. Colour information is permanently discarded during grayscale conversion and cannot be recovered. This is a one-way process — once converted, you need the original colour image to get colour back.

What formats are supported?

JPEG, PNG, and WebP images up to 100MB are supported. The output format matches the input format.

Is the conversion done in my browser or on a server?

The conversion runs entirely in your browser using the Canvas API. Your images are never uploaded to any server.