Create picture thumbnails

Originally created by Miha Filej, @mfilej

This guide is a part of the Rails Girls workshop main guides. Make sure you follow the numbered guides in order before continuing.

The Internet is all about speed. The faster your page loads, the less likely people are to click away. And we want people to stick around to share our great ideas with our ideas app! Also, people with data plans visiting your website will thank you for requiring less data to be transmitted.

One way to speed up page loads is by displaying images in a smaller size. The smaller an image is, the fast it will be transmitted over the Internet.

Install ImageMagick

We’ll be using the ImageMagick tool to resize the pictures uploaded to your ideas.

Run the following command in the Terminal app:

brew install imagemagick

If you are on Ubuntu, run the following command in the Terminal app:

sudo apt-get update
sudo apt-get install -y imagemagick

Download and run the ImageMagick installer (use the first download link). In the installation wizard, make sure you check the checkbox to install legacy utilities.

Help from the coach

Explain what is ImageMagick and how is it different from libraries/gems we used before?

Install a Ruby gem for ImageMagick

For Ruby to talk with ImageMagick, we’ll be using the mini_magick Ruby gem. First we will need to add it to our app and install it.

Open Gemfile in your Text Editor and add this line:

gem "mini_magick"

below the line:

gem "carrierwave"

In the Terminal app run this command:

bundle install

Make sure to (re)start your Rails server after installation.

Tell your app to create thumbnails

Now that we have a way to talk to ImageMagick through the mini_magick Ruby gem, we can tell the file upload gem carrierwave to create thumbnails for every picture you upload.

Open app/uploaders/picture_uploader.rb and find the line that looks like this:

# include CarrierWave::MiniMagick

Remove the # sign at the front of the line.

Help from the coach

Explain the concept of comments in code.

Below the line you just changed, add these lines:

version :thumb do
  process :resize_to_fit => [150, 150]

The images uploaded from now on will be resized to a smaller size, but the ones we already have haven’t been updated. Instead, let’s edit an idea and add a new picture. When saved the idea now has a thumbnail for the uploaded picture.

Display the thumbnail

We haven’t changed how the idea pictures are displayed, so it should still be showing the original larger image. Let’s change the views to display the thumbnail instead.

Open app/views/ideas/_idea.html.erb and change the line:

<%= image_tag(idea.picture_url, width: 150, height: 150, class: "img-thumbnail flex-shrink-0") if idea.picture? %>

to this line:

<%= image_tag(idea.picture_url(:thumb), width: 150, height: 150, class: "img-thumbnail flex-shrink-0") if idea.picture? %>

Take a look at the list of ideas in the Browser to see if your ideas now have a thumbnail.

Help from the coach

Explain what specifying the image width in HTML and how it differs from resizing images on the server. Both images may look small, but only one is resized as a thumbnail.

If you’re ever stuck during a guide, please ask your coach for help and also consult this handy cheatsheet for Ruby, Rails, the console, the Text Editor etc.


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