What the Grayscale PDF Converter does
This converter turns a colour PDF into a grayscale one in two ways. Convert colours rewrites the PDF itself: every colour setting in the page drawings, gradients, annotation colours and images is replaced with its grey equivalent, so text stays selectable and vector graphics stay sharp. Rasterise pages draws every page as a grey image at the resolution you choose, which is always complete but turns text into pictures.
You get a before-and-after preview of any page, the size of the new file compared with the original, and a list of anything the colour conversion could not handle, so a colour element is never left behind without you knowing. The PDF is processed in your browser and never uploaded.
How to use it
- Drop a PDF, or load one of the examples.
- Keep Convert colours for documents with text you want to search and copy. Choose Rasterise pages if you need a guaranteed all-grey file, for example for a print service that rejects any colour.
- Select Convert to grayscale. For rasterising, pick the resolution first: 150 dpi is fine for office printing, 300 dpi for sharp print.
- Compare the original and grayscale previews - change the page number to check others - read any warnings, then download the grayscale PDF.
Reading the results
Colour settings counts the colour operators rewritten in page, form and annotation drawings: RGB (rg/RG), CMYK (k/K) and colour-space colours (cs/sc) are all replaced with grey (g/G).
Images are decoded and stored as 8-bit DeviceGray. JPEG photos are decoded by your browser and re-stored losslessly, so no second round of JPEG artefacts is added - but the file can grow. Gradients (axial and radial shadings with exponential or stitched colour functions, which most applications write) are converted by rewriting their end colours.
Left in colour lists what could not be converted exactly: images in JPEG 2000 or CMYK JPEG, spot colours whose tint function is not a simple formula, gradients with sampled functions, and colour spaces the tool does not recognise. Each is named; Rasterise pages handles all of them.
Grey levels use the ITU-R BT.601 luma weights (0.299 R + 0.587 G + 0.114 B). That is why pure red becomes 30 % grey but pure green 59 %: the eye sees green as brighter. CMYK is converted with a simple ink-coverage formula without an ICC profile, which is close for office documents but not a colour-managed print conversion.
Worked example: a colour-coded chart that stops being readable
The colour report example is two pages printed from a web page. Convert colours rewrites 40 colour settings and leaves nothing in colour; the file grows by only a few hundred bytes (59.6 KB to 60.0 KB) and every word is still selectable. The dark blue heading (#1F4E79, RGB 31, 78, 121) becomes grey 0.299 x 31 + 0.587 x 78 + 0.114 x 121 = 68.8 out of 255 - a dark grey that still reads as a heading.
The bar chart shows why a preview matters. Its red, green and blue bars (RGB 229, 57, 53; 67, 160, 71; and 30, 136, 229) become greys of 108, 122 and 115 - three almost identical mid-greys - while the yellow bar (253, 216, 53) becomes a light 208. A chart that relied on colour alone will need labels or patterns before it is printed in black and white.
The scanned example is 33.7 KB and has one 850 x 1,100 pixel JPEG photo of a page. Convert colours decodes it in the browser and stores it as lossless 8-bit grey, so the file grows to 44.7 KB (133 %). Rasterising the same three pages at 150 dpi gives a 189 KB file, because every page - including the one that was plain text - becomes a full-page image: rasterising is the complete option, not the small one.
Formulas and scoring rules
- RGB to grey
grey = 0.299 R + 0.587 G + 0.114 BComponents from 0 to 1; images use 0 to 255 and are rounded to the nearest whole level.- CMYK to grey
grey = 1 - min(1, 0.3 C + 0.59 M + 0.11 Y + K)An approximation without a colour profile; 100 % K alone gives black.- Raster size
pixels = page width in inches x dpi by page height in inches x dpiA US Letter page at 150 dpi is 1,275 x 1,650 pixels.
Limitations: what the result does not prove
- Encrypted PDFs are refused, because rewriting them would break their protection.
- Convert colours does not use colour profiles. Output intents, ICC-based spaces and CMYK are converted with the formulas shown, so the result is right for office printing but is not a substitute for a print shop's colour-managed grayscale conversion.
- Transparency groups, soft masks and blend modes keep their settings; a few complex overlapping effects may render with slightly different greys than a full colour-managed conversion.
- Rasterised output replaces text with images: it is no longer selectable, searchable or accessible to screen readers, and form fields and links are removed. Keep the original.
- Rasterising is limited to 300 pages per file here, and pages are capped at 40 million pixels each.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- ITU-R Recommendation BT.601 - Studio encoding parameters of digital television (luma coefficients)
- ISO 32000-2:2020 PDF 2.0, section 8.6 Colour spaces and 8.7 Patterns
- Adobe - PDF Reference, sixth edition (PDF 1.7), sections 4.5 Color spaces and 3.9 Functions
- Mozilla - pdf.js (the renderer used for previews and rasterising)
Frequently asked questions
How do I convert a PDF to black and white without losing text quality?
Use Convert colours. It rewrites the colour instructions inside the PDF instead of turning pages into pictures, so text stays vector text - sharp at any zoom and still selectable and searchable - while every colour becomes grey.
Why does my grayscale PDF still show some colour?
Some content cannot be converted exactly by rewriting: JPEG 2000 or CMYK JPEG images, spot colours with complex tint functions and some gradients. The tool lists each one after converting. Choose Rasterise pages to guarantee there is no colour left.
Why did the file get bigger?
Colour JPEG photos are decoded and stored as lossless grey so that no extra JPEG damage is added, and lossless storage is larger than JPEG. Rasterising usually makes text documents much larger still, because every page becomes an image. If size matters, run the grayscale file through a PDF compressor afterwards.
Which formula is used to turn colour into grey?
The ITU-R BT.601 luma weights: 0.299 x red + 0.587 x green + 0.114 x blue. It matches how bright colours look to the human eye, which is why green turns into a lighter grey than blue of the same strength.
Will printing in grayscale save ink?
It avoids colour cartridges, but many printers still mix a little colour ink into grey and black. A grayscale PDF makes sure the file itself contains no colour; the printer's own grayscale or black-only setting decides which inks are used.
Does the converted PDF keep links and form fields?
With Convert colours, yes: links, bookmarks, form fields and text all stay, only colours change. With Rasterise pages, each page becomes a single image, so links, fields and selectable text are lost.
Last reviewed by the A2Z.Tools team against the sources listed above.
