Ruby thumbnail generator is simple script which is ideal to use in your Ruby on Rails application to quickly generate thumbnails of any proportions. Just set width and height and get the image.

1. copy following code into /controllers/thumb_controller.rb

2. edit /config/routes.rb and add this line:
map.connect “thumb/*specs”, :controller => “thumb”, :action => “index”

3. create directory /imagelib/ in RoR’s /public/ directory and
/image_cache/ inside /imagelib/ directoory

Now you can call /thumb/photo.jpg?w=400&h=350 and you will
see resized picture “photo.jpg”. photo.jpg should be stored in
/public/imagelib/ directory. Off course you can change directory
structure if you wish just don’t forget to edit thumb_controller.rb
than.

visit www.cleverleap.com/ruby-thumbnail-generator/
for more information

class ThumbController < ApplicationController

  require 'gd2'
  include GD2

  def index

    path = "imagelib/"    # default image library directory

    widthx = 500          # default width of generated image
    heightx = 500         # default height of generated image

    if params[:w] then widthx = params[:w].to_i

    end

    if params[:h] then heightx = params[:h].to_i

    end

    filepath = path + params[:specs].join("/")    # Path to file

    format = filepath.split(".").last             # Format - extension

    filename = params[:specs].last.split(".").first # just file name without extension

    #require 'digest/md5'
    digest = Digest::MD5.hexdigest( filepath )      # md5 hash

    cachefile = digest + "-" + widthx.to_s + heightx.to_s + "." + format

    picfile = filepath
    cachedpicfile = path + "image_cache/" + cachefile

    if File.exists?(cachedpicfile) && (File.stat( cachedpicfile ).mtime.to_i > File.stat( picfile ).mtime.to_i)

      picsource = cachedpicfile
      cache = true
    elsif File.exists? picfile
      picsource = picfile

    end

    if cache == true    # Read from Cache
      @pic = File.new(picsource).read

    else                # Import an image
      i = Image.import(picsource)

      if i.size[0] > i.size[1]  # Horizontal proportion. width > height.

        if i.size[0] < widthx then width = i.size[0]     # preffer smaller image width

        else width = widthx
        end

        height = width * i.size[1] / i.size[0]

      else                      # Vertical proportions
        if i.size[1] < heightx then height = i.size[1]

        else height = heightx
        end

        width = i.size[0] /(i.size[1] / height)
      end

      i.resize! width, height

      if format == "gif" then @pic = i.gif

      elsif format == "png" then @pic = i.png

      else @pic = i.jpeg 80
      end

      i.export(path + 'image_cache/' + cachefile ) # export cache file

    end

    cgi = CGI.new
  	cgi.out("type"=>"image/jpeg") { @pic }

  	render :nothing => true

  end
end