How to use it
- Choose the colour PDF. Its page count appears under the file name.
- Choose the Picture resolution: 150 dpi suits most documents, and 300 dpi keeps small print sharp.
- Click Make greyscale PDF and download the new file. Open it once to check the pages, because their text is now part of a picture.
How a colour becomes grey
Each pixel of a page is drawn, and its red, green and blue values are combined into one grey value with the weights of ITU-R BT.601, the standard for studio video: 0.299 for red, 0.587 for green and 0.114 for blue. The weights add up to 1, so white stays white and black stays black.
The weights are applied to the values the browser draws, so the grey is an approximation of a greyscale print, not a colour-managed conversion. A pure green pixel becomes a lighter grey than a pure red one, because green has the largest weight.
Why each page becomes a picture
A PDF page is a drawing whose colours are set by many instructions, and the pictures inside it have colours of their own. The reliable way to make a whole page grey is to draw it and turn the drawing to grey, so each page is saved as a picture of the size it has in the original.
The text of the pages is part of those pictures. It can no longer be selected, searched or copied, and the links and comments of the pages are not carried over.
Example: a colour brochure at 150 dpi
A four-page brochure has a pure red heading on page 1 and a pure green line on page 2. With the BT.601 weights, the red becomes a grey of 76 out of 255, and the green a grey of 150.
The new file keeps four pages, each the same size as before, now made of greyscale pictures.
Frequently asked questions
Are my PDF files uploaded anywhere?
No. Your browser draws each page, turns its colours to grey and builds the new file on your own device. Nothing is sent to our server.
Can I still select the text after making the file greyscale?
No. Each page is a picture, so its text cannot be selected, searched or copied. Keep the colour file if you need the text later.
Why do some colours become similar greys?
Each colour is turned into one grey value, so two colours that look different can end up as close shades. The BT.601 weights decide the grey, and they are the same for every page.
Which resolution should I choose?
150 dpi suits most documents on screen and in print. 300 dpi keeps small print sharp but makes a larger file, and 72 dpi makes the smallest file with the softest text.
Does the greyscale file keep the size of each page?
Yes. Each page is drawn at the size it has in the original, and its greyscale picture fills that page.
Sources
- ITU-R Recommendation BT.601-7, section 2.5.1: the luminance weights 0.299, 0.587 and 0.114
- pdf.js, the open-source PDF renderer that draws each page in your browser
Figures and text last checked on Thursday, November 12, 2026.