Grayscale without turning pages into pictures
The easy way to make a PDF gray is to draw every page as an image, turn the image gray and save the images as a new PDF. It works, and it ruins the file: text can no longer be selected, searched or read aloud by a screen reader, small print goes soft, and the file grows. This tool does the harder thing and changes the colors inside the PDF itself — the color of every piece of text and every line and shape, every photo, every gradient, and the colors of comments and form fields.
We measured the difference on two text documents printed from a browser:
| Document | Original | This tool | Pages as images, 150 dpi | Pages as images, 200 dpi |
|---|---|---|---|---|
| 3-page report | 90 KB | 80 KB, 1,638 of 1,638 words selectable | 1.40 MB, 0 selectable | 2.13 MB, 0 selectable |
| 5-page article with links | 37 KB | 32 KB, 1,837 of 1,837 words selectable | 1.72 MB, 0 selectable | 2.55 MB, 0 selectable |
The image versions are 17 to 80 times larger, and not one word in them can be copied.
Every page is checked afterwards
PDFs can hold color in many places: spot inks such as Pantone colors, color palettes, gradients, repeating patterns, CMYK photos, color profiles. After converting, the tool draws each page of the new file again and checks it pixel by pixel for any color that is left. It also compares each page with the original, so a mistake such as a CMYK photo coming out as a negative cannot slip through.
If a page fails either check, that one page — and only that page — is rebuilt as a 200 dpi grayscale image, and the report says which page and why, for example “Page 5 was turned into a grayscale image. It uses a color mesh gradient.” The other pages keep their text. In our test file of every color feature we could build (RGB, CMYK, color-profile, Lab, spot and multi-ink colors, palette, 16-bit, masked and transparent images, photos, gradients, patterns, a highlight comment and a form field), four of five pages converted as vectors and the fifth, a free-form mesh gradient, became an image as expected. 21 measured points on those pages matched the expected gray within a few levels.
How colors become gray
By brightness, the way your eye sees them, not by a plain average. RGB colors use the standard luma weights: 0.299 × red + 0.587 × green + 0.114 × blue. Pure yellow becomes a light gray (89%) and pure blue a dark one (11%), which is why a yellow highlight stays readable and blue text stays dark. CMYK colors use the conversion given in the PDF standard, and spot colors are converted through their own ink definitions, so a Pantone red becomes the gray of that red rather than a guess.
Two colors of the same brightness become the same gray. A pie chart that tells red from green only by color may be hard to read afterwards — worth a look before you print a hundred copies. The page previews below the download show every page of the result.
Real gray, not “gray-looking”
Photos are saved with a single gray channel. Browsers can only save JPEG files in color, so a gray photo saved by the browser is still a color image whose three channels happen to match, and some printers print such “black” using all their inks. This tool writes its own single-channel JPEG, which is also smaller: the test photo went from 6.9 KB to 3.8 KB. Text and drawing colors are written as gray values, so the file contains nothing but black ink amounts.
When to use it
- Printing on an office printer that charges color rates for any page with color on it.
- Forms, applications and court filings that must be submitted in black and white.
- Checking how a document will look when photocopied or printed on a black-and-white laser.
- Shrinking a PDF full of color photos — one channel instead of three.
Nothing is uploaded: the PDF is converted inside your browser tab. There is no hourly limit, no page limit and no sign-in. Bookmarks, links and form fields keep working. Password-protected files need to be unlocked first with Unlock PDF, and if you only need a smaller file, Compress PDF keeps the colors.