emf-to-png

Convert EMF files to PNG or JPEG in Node.js without Office, LibreOffice, or Inkscape.

This package is built for the common DOCX extraction case where images appear as .emf files and need to be rendered on a server or in a Node.js pipeline.

Status

EMF support is working for classic EMF files through a bundled WebAssembly build of libemf2svg, followed by rasterization with @resvg/resvg-js.

WMF and EMF+ are not part of the current stable API yet. Some advanced or application-specific EMF records may still fail depending on upstream renderer coverage.

Install

npm install emf-to-png

Usage

import { convert, convertFile } from "emf-to-png";
import { readFile } from "node:fs/promises";

await convertFile("diagram.emf", "diagram.png", { width: 1200 });

const input = await readFile("diagram.emf");
const png = await convert(input, {
  width: 1200,
  background: "#ffffff",
  format: "png",
});

CLI

npx emf-to-png input.emf output.png

Environment options:

EMF_PNG_WIDTH=1200
EMF_PNG_HEIGHT=800
EMF_PNG_DPI=96
EMF_PNG_BG=#ffffff
EMF_PNG_FORMAT=png

API

convert(input: Buffer | Uint8Array, options?: ConvertOptions): Promise<Buffer>
convertFile(inputPath: string, outputPath?: string, options?: ConvertOptions): Promise<string>
emfOrWmfToSvg(kind: "emf", data: Uint8Array, dpi?: number): Promise<string>

ConvertOptions:

interface ConvertOptions {
  width?: number;
  height?: number;
  background?: string;
  dpi?: number;
  format?: "png" | "jpeg";
  fallback?: boolean;
  logger?: (message: string) => void;
}

By default, conversion errors throw. Set fallback: true if you prefer a placeholder PNG instead.

Development

Build the EMF WebAssembly renderer with Docker:

npm run build:wasm

Build the JavaScript package:

npm run build:js
node scripts/postbuild-copy-wasm.mjs

Run tests:

npm test

Full build:

npm run build