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Fast convertion/scaling of images using a pool of long lived graphicsmagick processes

npm install graphicsmagick-stream

Build Status

It works by spawning and reusing a custom graphicsmagick processes (see src/) that accepts images over stdin and pipes out the converted result over stdout


var gm = require('graphicsmagick-stream')
var fs = require('fs')
var convert = gm({
  pool: 5,             // how many graphicsmagick processes to use 
  format: 'png',       // format to convert to 
  scale: {
    width: 200,        // scale input to this width 
    height: 200,       // scale input this height 
    type: 'contain'    // scale type (either contain/cover/fixed) 
  crop: {
    width: 200,        // crop input to this width 
    height: 200,       // crop input this height 
    x: 0,              // crop using this x offset 
    y: 0               // crop using this y offset 
  page: [1,5],         // only render page 1 to 5 (for pdfs) 
                       // set to a single number if you only want to render one page 
                       // or omit if you want all pages 
  rotate: 'auto',      // auto rotate image based on exif data 
                       // or use rotate:degrees 
  density: 300,        // set the image density. useful when converting pdf to images 
  split: false,        // when converting pdfs into images it is possible to split 
                       // into multiple pages. If set to true the resulting file will 
                       // be a tar containing all the images. 
  tar: false           // stream a tar containing the image. This is forced to `true` 
                       // if split is set to `true` 
    // override any of the above options here 

You do not need to set all the options. If you only want to scale an image do

var stream = convert({
  scale: {
    width: 400,
    height: 300

You can also use it to get metadata info about an image using

var info =, info) {
  console.log(info) // prints something like {width:500, height:400, format:'png'} 

For more examples and usage see the test folder

Scale types

  • contain sets the scaled image to maximum have a width/height of the scale box. Always respects ratio.
  • cover sets the scaled image to at least have one of the width/height within the scale box. Always respects ratio.
  • fixed sets the scaled image to precisely the given width/height of the scale box. If both width/height is given it does not respect the ratio.

PDF Conversion

If you install ghostscript as well you will be able to convert pdfs to images by simply piping in a pdf and setting output format to jpeg (or another image format).

If you are rendering a multipage pdf scale.height will set the height of each page. To force scale.height to donate the height of the entire image set scale.multipage = true.

Use split = true to output each page as an image file. This will result in a tar file containing all the images, so you will need to untar them on the other end. Use a project like tar-stream to achieve this.


You need to install libgraphicsmagicks in order to compile this.

Using OS X and Homebrew

brew install graphicsmagick --build-from-source
brew install libarchive

You will have to build the binary using the following command

gcc src/*.c -o bin/convert -L/usr/local/opt/libarchive/lib -I/usr/local/opt/libarchive/include -larchive -O `GraphicsMagickWand-config --cflags --cppflags --ldflags --libs`

Using Ubuntu

sudo apt-get install build-essential libgraphicsmagick++1-dev libarchive-dev

Then npm install should work.