Thumbnail Generation

Common use cases for thumbnails are pretty easy with Paperclip. You define your preferred sizes in your initial has_attached_file call:

class User < ActiveRecord::Base
  # Paperclip
  has_attached_file :photo,
    :styles => {
      :thumb => "100x100#",
      :small  => "150x150>",
      :medium => "200x200" }
end

Then you use them like this:

<%= image_tag @user.photo.url %>
<%= image_tag @user.photo.url(:thumb) %>
<%= image_tag @user.photo.url(:small) %>

Resizing options

Default behavior is to resize the image and maintain aspect ratio (i.e. the :medium version of a 300×150 image will be 200×100). Some commonly used options are:

• trailing #, thumbnail will be centrally cropped, ensuring the requested dimensions.
• trailing >, thumbnail will only be modified if it is currently larger requested dimensions. (i.e. the :small thumb for a 120×80 original image will be unchanged)

You can see a complete list of ImageMagick options for more.

Generating/regenerating your thumbnails

You can (re)generate your thumbnails en masse with Paperclip’s rake tasks. Using our example class above:

rake paperclip:refresh:thumbnails CLASS=User

If you are using the gem required version of paperclip the rake tasks may not be auto-loaded, but you can copy them into your lib/tasks directory if needed.

If you need more manual control or have a lot of thumbnails and only want to process a few, you can use #reprocess! like so:

users_to_reprocess.each do |user|
  user.photo.reprocess!
end