pdf-fs-reducer

Reduce PDF file size by downsampling embedded images through Ghostscript.

Prerequisites

Ghostscript must be installed and available in your system PATH.

| Platform | Install command / link | | --- | --- | | macOS | brew install ghostscript | | Ubuntu / Debian | sudo apt install ghostscript | | Windows | https://www.ghostscript.com/download/gsdnld.html |

Usage

npx pdf-fs-reducer <input.pdf> [options]

Examples

# default mode (ebook preset)
npx pdf-fs-reducer report.pdf

# custom output file path
npx pdf-fs-reducer report.pdf -o report.reduced.pdf

# smallest output for screen viewing
npx pdf-fs-reducer report.pdf --preset screen

# force custom image DPI (overrides preset)
npx pdf-fs-reducer report.pdf --dpi 120

# reduce quality by 30% from base DPI
npx pdf-fs-reducer report.pdf --size 30

# high quality print-oriented output
npx pdf-fs-reducer report.pdf -p printer -o report.print.pdf

Options

| Flag | Description | Default | | --- | --- | --- | | <input> | Input PDF path (required positional argument) | n/a | | -o, --output <path> | Output PDF path | <input-basename>.reduced.pdf in same directory | | -p, --preset <name> | Quality preset (screen, ebook, printer, prepress) | ebook | | -d, --dpi <number> | Custom DPI, overrides --preset | n/a | | -s, --size <percent> | Reduce quality by percentage (example: 30 means 30% lower quality) | n/a | | -c, --compatibility <ver> | PDF compatibility level | 1.4 | | -V, --version | Show version | n/a | | -h, --help | Show help | n/a |

Presets

| Preset | DPI | Best use | | --- | --- | --- | | screen | 72 | smallest size, on-screen viewing | | ebook | 150 | balanced quality and file size | | printer | 300 | high-quality printing | | prepress | 300+ | maximum quality for publishing |

Programmatic API

Install:

npm install pdf-fs-reducer

Use in Node.js:

const { PdfFilesizeReducer } = require("pdf-fs-reducer");

async function run() {
  const result = await PdfFilesizeReducer.reduce({
    input: "./input.pdf",
    output: "./output.pdf",
    preset: "ebook",
    size: 30,
    compatibility: "1.4"
  });

  console.log(result);
}

run().catch(console.error);

Return value:

{
  inputPath: "absolute-input-path",
  outputPath: "absolute-output-path",
  inputSize: 123456,
  outputSize: 98765,
  saved: 24691,
  percent: 19.99,
  effectiveDpi: 105,
  qualityReduction: 30
}

Sample output

pdf-fs-reducer
------------------------------------------------------------
Input : C:\docs\report.pdf (8.91 MB)
Output: C:\docs\report.reduced.pdf
Mode  : eBook (150 DPI) - balanced quality and size
Engine: gswin64c
------------------------------------------------------------
- Processing PDF (3s)
Completed.
Original: 8.91 MB
Reduced : 3.72 MB
Saved   : 5.19 MB (58.2% reduction)
Saved to: C:\docs\report.reduced.pdf

How It Works

pdf-fs-reducer calls Ghostscript (pdfwrite) to rebuild the PDF with lower image resolution.
In custom DPI mode, images are downsampled with bicubic interpolation.
With --size, the tool converts quality reduction percentage into an effective DPI (baseDPI * (1 - size/100)).
Text and vector drawing instructions are preserved, so reductions mainly come from image-heavy pages.

License

MIT