Grayscale PDF

Runs in browser PDF Optimization

Page mode renders every page as a grey image (all colour goes, text becomes an image); image mode recolours the embedded pictures and leaves text and vector graphics untouched. Both run locally.

Privacy: Processed locally in your browser. Your file is not uploaded.

How does PDF compression work?

Most of a PDF's size is images and embedded fonts, not text. Optimisers combine several techniques: re-encoding images at a lower resolution or quality (JPEG for photos, lossless Flate for line art), subsetting fonts to the glyphs actually used, removing unused objects, duplicate resources and metadata, and linearising the file so a browser shows the first page before the download finishes. Not every tool uses all of them. These techniques keep the text layer, links and structure; rasterising whole pages into images, the most aggressive option, turns text into pixels and loses them.

Read the guide: PDF Compression Explained

How to use Grayscale PDF

  1. Drop a PDF.
  2. Choose the mode.
  3. Click "Convert to grayscale".
  4. Download.

Grayscale PDF features

  • Page mode: every page rendered as a grey image
  • Image mode: only embedded images recoloured, text stays text
  • DPI and quality controls
  • Before / after sizes
  • Clear warning when text becomes an image
  • Local processing

Grayscale PDF example

Prepare a colour brochure for mono printing

Input:

brochure.pdf, mode: whole pages, 150 DPI, quality 85

Output:

brochure-grayscale.pdf — 8 grey pages; warning: text is now an image

Frequently asked questions about Grayscale PDF

Why are there two modes?

Colour lives in text, vector graphics and images. Recolouring vectors without rendering is not reliable, so page mode renders the whole page to a grey image, while image mode converts only the pictures and keeps text selectable.

Does page mode lose the text?

The text is still visible but becomes part of an image — it is no longer selectable or searchable. Use image mode or OCR the result if you need text.

Is the file smaller afterwards?

Often, since grey JPEGs are smaller than colour ones; the result shows the before and after sizes.

Is my PDF uploaded to a server?

No. The file is opened and processed by your browser with WebAssembly and JavaScript; nothing is sent to Mutqan Soft or anyone else. Close the tab and the file is gone. Downloading the result needs a free account — no subscription, no payment.

Can I use it on a password-protected PDF?

Yes, if you know the password: the file list asks for it once and every operation then works on the decrypted pages. The output is saved without a password unless you protect it again.

Technical notes

Page mode renders with pdf.js, converts the canvas to luminance (Rec. 601 weights) and rebuilds the document from JPEG pages of the original size. Image mode decodes each image, converts to grey and writes it back as a DeviceGray JPEG; vector colour is untouched because content-stream recolouring cannot be done reliably without rendering.

References