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Convert an image to grayscale

Every colour turned into the grey of the same brightness, for one image or a folder.

Convert JPG, PNG, WebP or HEIC images to grayscale in your browser, one or a batch, with a live preview. It is free, needs no account and adds no watermark, and your files are not uploaded: everything runs in your browser on your device. The size limit is your device’s memory, and phones hold less; give the page a short while after one visit to save itself for offline use, and then it works offline.

Drop images to convert to grayscaleor click to choose files. Batches welcome.
    Working…

    Done

    Your files are processed on this device and never sent to a server. Reload the page to clear everything from memory.

    Grayscale is the honest version of black and white: each pixel keeps its brightness and loses its colour, weighted the way the eye sees it, so a green field and a red jacket turn into the greys you would expect rather than the same flat tone.

    Designers use it to check whether a layout still reads without colour, developers to make a disabled or inactive state of an icon, teachers and offices to print handouts on a mono printer, and people with a colour-heavy screenshot to make it easier on the eye in a report. PNG and WebP keep their transparency, so logos and icons come out clean.

    Drop the images and the first one previews the result. Converting a batch takes seconds, the files never leave your device, and nothing is added to them: no watermark and no metadata.

    How it works

    1. Drop one or more images.
    2. Check the preview, and pick the format if you want something other than the original.
    3. Press Convert to grayscale and download the images.

    In your browser, not on a server

    Your browser decodes each image (libheif or the Squoosh decoders step in for HEIC, AVIF and JPEG XL) and draws it on a canvas in your tab. Each pixel’s brightness is computed with the Rec. 709 weights, the way the eye weighs red, green and blue. High contrast stretches the tones to the full range; pure black and white picks the split point with Otsu’s method, which finds the threshold that best separates ink from paper. The browser then saves the canvas as JPG, PNG or WebP.

    Compared with upload-based tools: Photo filter sites upload your pictures to apply a filter a phone could do offline, and many add a watermark or keep the images. Here the photos stay on your device, the limit on how many you convert at once is your device’s memory (phones hold less), and the result is not recompressed more than once.

    Verify it yourself. Give the page a short while after one visit to save itself for offline use, then turn off Wi-Fi or switch to airplane mode and run the tool again. Or open your browser's developer tools (F12, or Cmd-Option-I on a Mac), pick the Network tab, and watch it while you convert. The panel above does the same count for you.

    Questions

    Why do some colours end up the same grey?

    Grayscale keeps brightness only, so two different colours of the same brightness, such as a mid red and a mid green, become the same grey. If they must stay apart, choose High contrast, which spreads the tones further.

    Does it work for icons and logos with a transparent background?

    Yes. Save as PNG or WebP and the transparent parts stay transparent; only the coloured pixels are changed.

    Which weights are used for red, green and blue?

    The Rec. 709 luma weights: about 21% red, 72% green and 7% blue. Green counts most because the eye is most sensitive to it, which is why a simple average of the three channels looks wrong, with blues too light and greens too dark.

    Can I check a website design for colour blindness this way?

    Grayscale shows whether your interface depends on colour alone, for example a red error and a green success message that look identical without colour. It is not a colour-blindness simulator, but it catches the same class of problem quickly.

    Will the file get smaller?

    Usually a little, because there is less colour detail for the encoder to store. For a much smaller file, run the result through the image compressor afterwards.

    Is the file uploaded anywhere?

    No. There is no server in this process. The page is a static file and the work is done by code running inside your browser tab. Give the page a short while after one visit to save itself for offline use; then you can turn off Wi-Fi and it still works.

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