class Paperclip::Thumbnail

Handles thumbnailing images that are uploaded.

def animated?

Return true if the format is animated 
def animated?
  @animated && (ANIMATED_FORMATS.include?(@format.to_s) || @format.blank?)  && identified_as_animated?
end

def convert_options?

Returns true if the image is meant to make use of additional convert options. 
def convert_options?
  !@convert_options.nil? && !@convert_options.empty?
end

def crop?

Returns true if the +target_geometry+ is meant to crop. 
def crop?
  @crop
end

def identified_as_animated?

Return true if ImageMagick's +identify+ returns an animated format 
def identified_as_animated?
  if @identified_as_animated.nil?
    @identified_as_animated = ANIMATED_FORMATS.include? identify("-format %m :file", :file => "#{@file.path}[0]").to_s.downcase.strip
  end
  @identified_as_animated
rescue Cocaine::ExitStatusError => e
  raise Paperclip::Error, "There was an error running `identify` for #{@basename}" if @whiny
rescue Cocaine::CommandNotFoundError => e
  raise Paperclip::Errors::CommandNotFoundError.new("Could not run the `identify` command. Please install ImageMagick.")
end

def initialize(file, options = {}, attachment = nil)

+animated+ - whether to merge all the layers in the image. Defaults to true
+format+ - the desired filename extension
+whiny+ - whether to raise an error when processing fails. Defaults to true
+convert_options+ - flags passed to the +convert+ command that influence how the image is processed
+source_file_options+ - flags passed to the +convert+ command that influence how the source file is read
+string_geometry_parser+ - an object with a method named +parse+ that takes a string and produces an object with +width+, +height+, and +to_s+ accessors. Defaults to Paperclip::Geometry
+file_geometry_parser+ - an object with a method named +from_file+ that takes an image file and produces its geometry and a +transformation_to+. Defaults to Paperclip::Geometry
+geometry+ - the desired width and height of the thumbnail (required)

Options include:

set, the options will be appended to the convert command upon image conversion
+whiny+ is true (which it is, by default. If +convert_options+ is
unless specified. Thumbnail creation will raise no errors unless
which is a "WxH"-style string. +format+ will be inferred from the +file+
will attempt to transform the image into one defined by +target_geometry+
Creates a Thumbnail object set to work on the +file+ given. It 
def initialize(file, options = {}, attachment = nil)
  super
  geometry             = options[:geometry].to_s
  @crop                = geometry[-1,1] == '#'
  @target_geometry     = options.fetch(:string_geometry_parser, Geometry).parse(geometry)
  @current_geometry    = options.fetch(:file_geometry_parser, Geometry).from_file(@file)
  @source_file_options = options[:source_file_options]
  @convert_options     = options[:convert_options]
  @whiny               = options.fetch(:whiny, true)
  @format              = options[:format]
  @animated            = options.fetch(:animated, true)
  @auto_orient         = options.fetch(:auto_orient, true)
  if @auto_orient && @current_geometry.respond_to?(:auto_orient)
    @current_geometry.auto_orient
  end
  @source_file_options = @source_file_options.split(/\s+/) if @source_file_options.respond_to?(:split)
  @convert_options     = @convert_options.split(/\s+/)     if @convert_options.respond_to?(:split)
  @current_format      = File.extname(@file.path)
  @basename            = File.basename(@file.path, @current_format)
end

def make

that contains the new image.
Performs the conversion of the +file+ into a thumbnail. Returns the Tempfile 
def make
  src = @file
  filename = [@basename, @format ? ".#{@format}" : ""].join
  dst = TempfileFactory.new.generate(filename)
  begin
    parameters = []
    parameters << source_file_options
    parameters << ":source"
    parameters << transformation_command
    parameters << convert_options
    parameters << ":dest"
    parameters = parameters.flatten.compact.join(" ").strip.squeeze(" ")
    success = convert(parameters, :source => "#{File.expand_path(src.path)}#{'[0]' unless animated?}", :dest => File.expand_path(dst.path))
  rescue Cocaine::ExitStatusError => e
    raise Paperclip::Error, "There was an error processing the thumbnail for #{@basename}" if @whiny
  rescue Cocaine::CommandNotFoundError => e
    raise Paperclip::Errors::CommandNotFoundError.new("Could not run the `convert` command. Please install ImageMagick.")
  end
  dst
end

def transformation_command

into the thumbnail.
Returns the command ImageMagick's +convert+ needs to transform the image 
def transformation_command
  scale, crop = @current_geometry.transformation_to(@target_geometry, crop?)
  trans = []
  trans << "-coalesce" if animated?
  trans << "-auto-orient" if auto_orient
  trans << "-resize" << %["#{scale}"] unless scale.nil? || scale.empty?
  trans << "-crop" << %["#{crop}"] << "+repage" if crop
  trans << '-layers "optimize"' if animated?
  trans
end