GruntFile.js

/*
 After you have changed the settings at "Your code goes here",
 run this with one of these options:
  "grunt" alone creates a new, completed images directory
  "grunt clean" removes the images directory
  "grunt responsive_images" re-processes images without removing the old ones
*/

module.exports = function(grunt) {

    grunt.initConfig({
      responsive_images: {
        dev: {
          options: {
            engine: 'im',
            sizes: [{
          
              // Change these:
              width: 500,
              suffix: '_small',
              quality: 60
              
            }]
          },
  
          /*
          You don't need to change this part if you don't change
          the directory structure.
          */
          files: [{
            expand: true,
            src: ['*.{gif,jpg,png}'],
            cwd: 'images_src/',
            dest: 'images/'
          }]
        }
      },
    });
    
    grunt.loadNpmTasks('grunt-responsive-images');
    // grunt.loadNpmTasks('grunt-contrib-clean');
    // grunt.loadNpmTasks('grunt-contrib-copy');
    // grunt.loadNpmTasks('grunt-mkdir');
    grunt.registerTask('default', ['responsive_images']);
    
  
  };