Rails paperclip generate thumbnail from other style

Question

I'm following the jcrop rails tutorial, but I've hit a snag. What it comes down to is the fact that paperclip is generating the thumbnail from the original file, but I need it to be generated from another style. The original file doesn't have any space between the product shot and the edge of the document. Therefore I can't crop further out. To combat that, I made another style which has white pixel padding. That's what I want to generate the thumbnail from.

# croppable is the one with the padding...it's what shows up in the crop view.
# I want :thumb to be generated from THAT style, not :original.
# When generating from :original, the crop offset/size is screwed because the dimensions of :original don't match :cropped
# and I can't crop beyond the pixel dimensions of :original.
has_attached_file :photo, :styles => {
                    :thumb => { :geometry => "300x300#", :format => :jpg, :processors => [:cropper] },
                    :general => ["150x375", :jpg],
                    :show => ["x425", :jpg],
                    :croppable => ["1200x1200>", :jpg]
        },
        :url  => "/assets/wines/:style/:wine_name",
        :path => ":rails_root/public:url",
        :default_url => ":wine_default",
        :default_path => ":rails_root/public:wine_default",
        :default_style => :show,
        :convert_options => {
            :thumb => '-gravity center -rotate -30',
            :croppable => '-gravity center -extent 1200x1200',
            :general => '-gravity center -extent 150x375 -quality 95',
            :all => '-quality 100 -antialias -flatten -background white -unsharp 0.3x0.3+5+0'
        },
        :processors => [:thumbnail, :compression]

Answer 1

I came across a processor that someone else had made online and used it for myself. Details can be found at http://pjkh.com/articles/speeding-up-thumbnail-generation-with-paperclip/ for advanced usage information.

recursive_thumbnail.rb (include in lib/paperclip_processors)

module Paperclip
    class RecursiveThumbnail < Thumbnail
      def initialize file, options = {}, attachment = nil
        super Paperclip.io_adapters.for(attachment.styles[options[:thumbnail] || :original]), options, attachment
      end
    end
end

and for your model:

:styles => {
    :croppable => ["1200x1200>", :jpg],
    :show => ["x425", :jpg],
    :general => ["150x375", :jpg],
    :thumb => {
        :geometry => "150x150^",
        :format => :jpg,
        :processors => [:recursive_thumbnail] },
        :thumbnail => :croppable
    }

Answer 2

Maybe this would help you or someone else like me who Google led to this question.

https://github.com/thoughtbot/paperclip/wiki/Thumbnail-Generation

Generating/regenerating your thumbnails

Note: regenerating only one of several defined styles as described in some of the examples below will lead to broken paths/urls for all other styles if you have :hash in your paperclip_defaults[:path] and :updated_at in your paperclip_defaults[:hash_data] (and you have by default). Don’t do this unless you really know what you’re doing.

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

bundle exec rake paperclip:refresh:thumbnails CLASS=User