fynepdf-grayscale

Make PDFs gray in place: text stays text, nothing is redrawn. The fynepdf-grayscale command line and a Node API, with no Ghostscript. Made by FynePDF for its web and desktop apps.

• Every colour, where it is: text and drawing colours, pictures, palettes, gradients, patterns, spot inks, and the appearances of comments and form fields.
• Nothing else changes: text stays selectable, and bookmarks, links, form fields, tags and attachments aren't touched.
• Photos keep their quality: most JPEGs are made gray without re-compressing them.
• Fast: a typical file takes 0.01 s; 1,067 files took 78 s, against 1,038 s for Ghostscript, which lost the text of 40 of them.

Install

npm install fynepdf-grayscale

It brings the command line for your platform (Linux x64 and arm64 with glibc 2.28+, Windows x64, macOS 11+ on Apple silicon and Intel). Nothing is downloaded at install time and no install script runs.

Command line

npx fynepdf-grayscale input.pdf output.pdf                    # every page
npx fynepdf-grayscale input.pdf output.pdf --pages 2-5,8      # only these pages
npx fynepdf-grayscale input.pdf output.pdf --only drawings    # text and drawings gray, photos in colour
npx fynepdf-grayscale input.pdf output.pdf --only images      # photos gray, text and drawings in colour

It prints what it did as one line of JSON.

Node

const { toGray } = require("fynepdf-grayscale"); // or: import { toGray } from "fynepdf-grayscale";

const result = await toGray("input.pdf", "output.pdf", { pages: [2, 3, 4], only: "drawings" });
console.log(`${result.converted} of ${result.pages} pages made gray`);

toGray rejects when the file can't be read (error.code "unreadable"), needs a password ("password"), doesn't have the pages asked for ("pages") or can't be written ("write"). Options: pages (an array or "2-5,8"), only ("drawings" or "images"), jpegQuality (default 90), signal. Types are included.

On a platform without a package, build the command line from the repository and set FYNEPDF_GRAYSCALE_BINARY to it.

More

How it works, the benchmark against Ghostscript and pages drawn as pictures, and the C++ library: github.com/fynepdf/fynepdf-grayscale.

MIT, © 2026 FynePDF. The libraries inside each platform package keep their own licences (licenses/).