Grayscale PDF
Turn a color PDF into grayscale or crisp black and white, ready for cheap printing or faxing. Pages are converted in your browser with pdf.js and pdf-lib, so your file is never uploaded.
Higher turns more light gray into black; lower keeps only dark text.
Pages are converted to images, so text is no longer selectable in the new PDF.
How to use the Grayscale PDF
- Open a PDF with the Open PDF button or drag it onto the drop area.
- Choose Grayscale or Black & white. For black and white, move the threshold slider until the preview looks clean.
- Pick the resolution and quality: 150 DPI is a good balance; use 300 DPI for small print.
- Press Convert and wait while each page is converted.
- Download the PDF and compare the new file size with the original.
How the conversion works
Each page is drawn exactly as a PDF viewer would show it (including form fields, stamps and comments that are visible on the page) using pdf.js. Every pixel is then converted to a gray value with the ITU-R BT.601 luminance formula:
Y = 0.299 × R + 0.587 × G + 0.114 × B
In black and white mode, pixels darker than the threshold become pure black (0) and all others pure white (255). The pages are saved as JPEG images into a new PDF built with pdf-lib, with each page kept at its original size, so a 210 × 297 mm A4 page stays A4 and Letter stays 8.5 × 11 inches.
| Color | RGB | Gray value (Y) |
|---|---|---|
| Pure red | 255, 0, 0 | 76 |
| Pure green | 0, 255, 0 | 150 |
| Pure blue | 0, 0, 255 | 29 |
| Yellow highlight | 255, 255, 0 | 226 |
| Brand green (#2f6b4f) | 47, 107, 79 | 86 |
This is why yellow highlighter almost disappears in grayscale while blue text becomes nearly black, and why a black and white threshold around 150–170 keeps text but drops light backgrounds.
Choosing resolution and quality
| DPI | A4 / Letter page in pixels | Best for |
|---|---|---|
| 72 | 595 × 842 / 612 × 792 | Smallest files, quick previews |
| 100 | 827 × 1169 / 850 × 1100 | Email attachments, screen reading |
| 150 | 1240 × 1754 / 1275 × 1650 | Office printing, recommended default |
| 200 | 1654 × 2339 / 1700 × 2200 | Small print, detailed diagrams |
| 300 | 2480 × 3508 / 2550 × 3300 | High-quality printing and archiving |
Why print in grayscale?
- Save color ink or toner. Many printers still use some color ink for "black" unless the document itself is grayscale.
- Predictable results on black-and-white laser printers, photocopiers and fax machines, where colors otherwise turn into muddy or invisible grays.
- Submission rules: some courts, schools and agencies ask for black and white documents.
To shrink the file further afterwards, try Compress PDF. If you need the pages as separate images instead, use PDF to JPG.
Frequently asked questions
How do I convert a PDF to black and white?
Open the PDF, choose Black & white, adjust the threshold if needed and press Convert. Every page is rendered, turned into pure black and white pixels and saved into a new PDF that you can download.
What is the difference between grayscale and black and white?
Grayscale keeps up to 256 shades of gray, so photos, charts and shading still look natural. Black and white uses only pure black and pure white, which gives the sharpest text for printing, faxing and scanning workflows, but photos turn into high-contrast silhouettes.
Will the text still be selectable?
No. Each page is converted into an image, so text can no longer be selected or searched. Keep the original if you need that, or run OCR afterwards. This is also why the conversion works with any PDF, including complex vector artwork.
Why is my grayscale PDF bigger than the original?
A text-only PDF stores letters as compact vector data, while the converted file stores a picture of every page. Lower the DPI to 100–150 or reduce the JPEG quality to make it smaller. For scanned or photo-heavy PDFs the grayscale version is usually smaller.
Which DPI should I choose?
150 DPI is enough for on-screen reading and normal office printing. Use 200–300 DPI for small print, fine lines or documents that will be printed professionally, and 72–100 DPI if you only need a small file to email.
How is the gray value calculated?
Each pixel's brightness is computed with the standard luminance formula Y = 0.299 × R + 0.587 × G + 0.114 × B, which matches how bright colors look to the human eye. Green therefore turns into a lighter gray than blue of the same intensity.