gulpfile.js

var gulp = require('gulp');
var gulpif = require('gulp-if');
var sprite = require('css-sprite').stream;
var base = require('gulp-base64');

// generate sprite.png and _sprite.scss
gulp.task('sprites', function () {
  return gulp.src('img/*.png')
    .pipe(sprite({
      name: 'tx.png',
      style: '_sprite.styl',
      cssPath: './img',
      processor: 'stylus'
    }))
    .pipe(gulpif('*.png', gulp.dest('img'), gulp.dest('stylus')))
});
// generate scss with base64 encoded images
gulp.task('icon', function () {
  return gulp.src('img/*.png')
    .pipe(sprite({
      base64: true,
      style: '_base64.styl',
      processor: 'stylus'
    }))
    .pipe(gulp.dest('stylus'));
});

gulp.task('base64', function () {
    return gulp.src('css/*.css')
        .pipe(base())
        .pipe(gulp.dest('img/'));
});