We want to convert all our header images to progressive JPEGs to give a good impression of the content to come, rather than having everything line by line. If you’ve installed GraphicsMagick you can use the excellent gm Node.js bindings to do so. This is some sample code, with an additional check if the conversion went well:

const gm = require('gm');
const isProgressive = require('is-progressive');
gm('aggressive.png')
  .strip() // Removes any profiles or comments. Work with pure data
  .interlace('Line') // Line interlacing creates a progressive build up
  .quality(90) // Quality is for you to decide
  .write('aggressive-progressive.jpg', (err) => {
    if(err) throw Error(err);
    console.log('Converted');
    isProgressive.file('aggressive-progressive.jpg')
      .then(progressive => console.log('Is progressive:', progressive));
  });

You can even use this in your builds. gulp-gm for instance makes these API bindings available in your Gulp builds.

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