Grayscale PDF
Convert to Black and White.
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Convert a PDF to grayscale, without uploading it
Turn a colour PDF into a black-and-white one for cheaper printing or a smaller file. Runs in your browser; note that it rasterises the pages.
Converting a PDF to grayscale is usually about printing. Colour pages cost several times more per sheet than monochrome ones, and print rooms frequently charge by whichever ink a page touches — so a report with one coloured logo on every page is billed as colour throughout. Stripping the colour before sending it to print is a real saving on a long document.
The other common reason is size. Colour information is a substantial part of what a scanned page weighs, and a grayscale version of a photographic document is often dramatically smaller.
There is a significant trade-off here, and it is the same one the aggressive compression mode makes: this conversion works by rendering each page as an image. That means the result has no text layer. We would rather you know that before you convert an important document than discover it when a search comes back empty.
Processed in your browser
Pages are rendered and recombined inside the tab. The document is never uploaded to a server.
Three quality levels
Choose the render resolution to balance print quality against file size, from roughly 72 to 216 DPI.
Often much smaller
Dropping the colour channels and re-encoding as grayscale JPEG makes photographic and scanned documents considerably lighter.
How to convert a PDF to grayscale
Select the colour PDF.
Pick a quality level for the render.
Each page is converted in your browser.
Download the grayscale document.
Conversion happens on your own machine
Pages are rendered, converted and reassembled inside your browser tab. The document is never uploaded, whether it is a report bound for the print room or something more sensitive.
When people reach for this
Cutting the cost of a print run
Print services charge substantially more per colour page, and often bill a page as colour if it contains any at all. On a long document with a coloured header, converting first can change the invoice significantly.
Meeting a submission requirement
Some tribunals, journals and archives specify monochrome documents. Converting is simpler than rebuilding the document from its source in black and white.
Shrinking a scanned document
A colour scan of text on white paper stores three channels to describe what is essentially black on white. Grayscale removes most of that redundancy.
Making a document neutral for review
Colour carries emphasis. A monochrome version puts every annotation and highlight on the same footing, which is occasionally what a review process wants.
What actually happens to your file
Each page is rendered to an offscreen canvas by pdf.js at a scale set by your quality choice: 1× for low, which works out around 72 DPI, 1.5× for medium, roughly 108 DPI, and 3× for high, roughly 216 DPI.
The canvas pixels are then walked and each one is converted using the standard luma formula — 0.299 times red, plus 0.587 times green, plus 0.114 times blue. Those coefficients are not arbitrary: they weight the channels according to how sensitive human vision is to each, which is why the result looks like a photographic black-and-white conversion rather than the flat, muddy grey that averaging the three channels produces.
Each converted page is encoded as a JPEG and embedded into a newly created PDF at the original page dimensions.
That last step is the one to understand. The output is a new document built from images, not your original document with its colours changed. Everything that made the pages text — the fonts, the character codes, the selectable text layer — is not carried across, because the page is now a picture of itself.
Where it falls short, honestly
- The text layer is destroyed. The converted PDF cannot be searched, selected, copied from or converted to Word. Keep your original; this is not a reversible operation.
- The file is not always smaller. For a document that was mostly text, replacing crisp vector type with a JPEG of it can easily produce a larger file than you started with. The saving is real for photographic and scanned pages, not for text ones.
- Quality is capped by the render scale. Even at the high setting, roughly 216 DPI is below what a print shop would call print quality, so fine detail will not survive as well as it would in a true colour-managed conversion.
- JPEG artefacts appear around text. Since the type is now an image, compression softens its edges, which is most visible on small print.
- Annotations, form fields, links and bookmarks are lost, because the document is rebuilt from images rather than edited.
- Long documents are slow and memory-hungry, since every page has to be rendered and processed pixel by pixel.
- If your goal is only cheaper printing, check your printer's settings first. Most print dialogs have a grayscale option that converts at print time without touching the file at all — a better outcome than this whenever it is available.
Compared with printing in grayscale
| This tool | Your printer's grayscale setting | |
|---|---|---|
| Keeps the text layer | No — pages become images. | Yes — the file is untouched. |
| Changes the file | Yes, permanently. | No. |
| Works when sending to a print shop | Yes — the file itself is monochrome. | No — they print what they receive. |
| Reduces file size | Often, for scanned pages. | No. |
| Where your file goes | Nowhere — it stays in the tab. | Nowhere. |
| Reversible | No. Keep the original. | Yes, it is only a setting. |