Grayscale PDF Converter

Turn a colour PDF into black and white

Printing in colour costs more ink, and many offices or schools only allow black-and-white submissions. The grayscale PDF converter removes all colour from a document while keeping the layout, images and page size. It is handy for draft prints, archived scans, accessibility checks of contrast, and forms that must be submitted in monochrome.

How the conversion works

Browsers cannot edit colour spaces inside a PDF directly, so the tool takes a reliable visual route. pdf.js renders every page to a canvas at the DPI you choose. Each pixel is then replaced by its luminance, calculated as 0.299 red + 0.587 green + 0.114 blue. The grey canvas is encoded as a JPEG with your chosen quality and placed on a page of the original size in a new document built with pdf-lib. A progress bar shows the current page, so even long documents give feedback.

Because every page becomes a picture, text is no longer selectable or searchable. If you need to keep searchable text, run OCR afterwards or use a desktop tool that edits colour spaces. Links, form fields and bookmarks are not carried over either.

Choosing quality and size

Resolution has the biggest effect on file size. At 100 DPI small text can look soft; 150 DPI is readable for most documents; 300 DPI preserves fine detail for printing but creates much larger files. JPEG quality between 60% and 80% usually looks clean for grey pages. Photo-heavy colour scans often shrink noticeably, whereas a simple text document can become bigger than the original, since vector text is replaced with pixels. The result message shows the old and new sizes, so you can rerun with different settings. Everything runs locally, which makes the tool suitable for confidential paperwork such as invoices, contracts and medical records.