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SafeTools

Convert a PDF to black and white

Your PDF is converted in this tab and never sent anywhere. Nothing is uploaded, stored or logged.

Black and white is not the same as grayscale: every pixel becomes either black or white, with no shades between. For scanned paperwork that usually means a much smaller file and cleaner printing, though the choice of threshold decides whether faint text survives. Both a global and an adaptive method are offered, with a live preview.

Drop your files here

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how your file is handled

  • It is read, not uploaded. The file is opened by JavaScript running in this tab and processed in memory, in a background worker.
  • The page cannot send it anywhere. This site is served with a Content-Security-Policy whose connect-src is 'self', so no script on the page is permitted to contact another server, even by mistake.
  • You can check it yourself. Open your browser's developer tools, switch to the Network tab and convert a file: nothing is sent. Or turn off your Wi-Fi first, because these tools keep working offline.

how to use it

  1. 01Drop your scanned PDF onto the box above.
  2. 02Choose Auto, or pick Otsu for clean digital pages and Adaptive for photographed or unevenly lit scans.
  3. 03Check the preview, adjust the threshold if needed, then convert and download.

questions

What is the difference between grayscale and black and white?
Grayscale keeps up to 256 shades per pixel, so photographs still look like photographs. Black and white keeps one bit per pixel: each one is either black or white. That is much smaller and prints sharply for text, but photographs on the page become coarse.
My scan has a gray shadow down one side. Which mode should I use?
Adaptive. A global threshold picks one cut-off for the whole page, so an uneven shadow either turns black or takes faint text with it when it is removed. Adaptive thresholding compares each pixel with its own neighbourhood, which handles uneven lighting from a phone camera or a thick book.
Why did my mostly-text PDF get bigger?
Because it was not a scan. Text stored as vector outlines is extremely compact; once a page is rendered to an image it is stored as pixels instead. Black and white output limits the damage, but a born-digital text PDF is usually best left alone.
Does the file leave my computer?
No. The conversion runs in this tab, the site has no server component, and its Content-Security-Policy restricts connect-src to 'self' so the page cannot send your document anywhere. You can disconnect from the network and it still works.

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