Using Imagemin with Gulp

Katie Hempenius
Katie Hempenius

Setup the Imagemin Gulp plugin

This Glitch already contains gulp, gulp-cli, and the gulp-imagemin plugin. To add the configuration for Imagemin, you'll need to edit your gulpfile.js file.

  • Click the Remix to Edit button to make the project editable.
  • First, initialize the gulp-imagemin plugin by adding this code at the top of gulpfile.js:
const imagemin = require('gulp-imagemin');
  • Next, replace the //Add tasks here comment in gulpfile.js with this code block:
gulp.src('images/*')
.pipe(imagemin())
.pipe(gulp.dest('images/'))

This code adds a Gulp task that uses Imagemin to compress the images in the images/ directory. The original images are overwritten and saved in the same images/ directory.

✔︎ Check-in

Your gulpfile.js file should now look like this:

const imagemin = require('gulp-imagemin');
const gulp = require('gulp');

gulp.task('default', () => {
gulp.src('images/*')
.pipe(imagemin())
.pipe(gulp.dest('images/'))
});

You now have a gulpfile.js that can be used to compress images.

Run Gulp

  1. Click the Tools button.
  2. Then click the Console button.
  3. Run Gulp to compress your images by typing the following command into the console:
gulp

When Gulp completes, you should see a message like this in the terminal:

gulp-imagemin: Minified 6 images (saved 50 kB—14.8%)

A 15% improvement in file size is a good start; however, more improvements can be made by using different compression settings.

Customize your Imagemin Configuration

imagemin-pngquant is a plugin for specifying compression quality levels. We've already added imagemin-pngquant to this project in the package.json file so that you can use it to compress your PNGs. To use it, declare the plugin and specify a compression quality level in your gulpfile.

  • Declare the imagemin-pngquant plugin by adding this line to the top of your gulpfile.js:
const pngquant = require('imagemin-pngquant');
  • Add the imagemin-pngquant plugin (and its settings) by passing the following array to ImageminPlugin():
[pngquant({quality: [0.5, 0.5]})]

This code tells Imagemin to compress PNGs using the Pngquant plugin. The quality field uses a min and max range of values to determine the compression level—0 is the lowest and 1 is the highest. To force all images to be compressed at 50% quality, pass 0.5 as both the min and max value.

✔︎ Check-in

Your gulpfile.js file should now look like this:

const pngquant = require('imagemin-pngquant');
const imagemin = require('gulp-imagemin');
const gulp = require('gulp');

gulp.task('default', () => {
gulp.src('images/*')
.pipe(imagemin([
pngquant({quality: [0.5, 0.5]})
]))
.pipe(gulp.dest('images/'))
});

But what about JPGs? The project also has JPG images; these need to be compressed too.

Customize your Imagemin Configuration (continued)

Use the imagemin-mozjpeg plugin, which has already been installed for you, to compress JPG images.

  • Declare the imagemin-mozjpeg plugin by putting this line at the top your gulpfile.js.
const mozjpeg = require('imagemin-mozjpeg');
  • Next, add mozjpeg({quality: 50}) to the array that's passed to ImageminPlugin():
[
pngquant({quality: [0.5, 0.5]}),
mozjpeg({quality: 50})
]

✔︎ Check-in

Your gulpfile.js file should now look like this:

const mozjpeg = require('imagemin-mozjpeg')
const pngquant = require('imagemin-pngquant');
const imagemin = require('gulp-imagemin');
const gulp = require('gulp');

gulp.task('default', () => {
gulp.src('images/*')
.pipe(imagemin([
pngquant({quality: [0.5, 0.5]}),
mozjpeg({quality: 50})
]))
.pipe(gulp.dest('images/'))
});

Re-run Gulp & verify results with Lighthouse

  • Re-run Gulp:
gulp

When Gulp completes, you should see a message like this in terminal:

gulp-imagemin: Minified 6 images (saved 667 kB—66.5%)

Hooray! These results are much better.

Lastly, it's a good idea to use Lighthouse to verify the changes that you just made.

Lighthouse's "Efficiently encode images" performance audit can let you know if the JPEG images on your page are optimally compressed.

  • To preview the site, mouse over the editor, press the App button, then the Show button.
  • Run the Lighthouse performance audit (Lighthouse > Options > Performance) on the live version of your Glitch and verify that the "Efficiently encode images" audit was passed.
Passing 'Efficiently encode images' audit in Lighthouse

Success! You have used Imagemin to optimally compress the images on your page.