How to use
- Choose a PDF file.
- Choose the quality — smaller file, balanced or sharp.
- Click Convert to black and white; the file downloads when it's done.
Options explained
- How it works
- Each page is rendered as an image at the chosen DPI, turned to greyscale and rebuilt into a PDF with the original page sizes.
- Quality
- 150 DPI suits ordinary documents; 300 DPI suits small print and fine lines.
How colours become grey
Each page is drawn at the chosen DPI. The scale is DPI ÷ 72, because PDF page sizes are in points of 1/72 inch, so a US Letter page (8.5 × 11 inches) becomes 1275 × 1650 pixels at 150 DPI, 1700 × 2200 at 200 DPI and 2550 × 3300 at 300 DPI. Every pixel is then replaced by its luminance, using the weights 0.299 for red, 0.587 for green and 0.114 for blue:
grey = 0.299 × R + 0.587 × G + 0.114 × BBecause the eye is most sensitive to green, pure green (0, 255, 0) becomes a light grey of 150, pure red becomes 76 and pure blue only 29. A blue line on white therefore prints darker than a green one. The grey pages are stored in the new PDF as JPEG images at quality 85, with the original page sizes kept.
Frequently asked questions
Why can't I select the text any more?
The pages are now images. For a black-and-white copy with selectable text, choose greyscale in your printer settings instead.
Why is the file bigger?
Text was vector data before; as images the pages take more space. 150 DPI gives a smaller file.
Is my file uploaded?
No. Everything happens in your browser.
Privacy
This tool runs entirely in your browser. Your files and text are processed on your device and are never uploaded to our servers.