dragonfly.rb

app = Dragonfly[:images]
app.configure_with(:imagemagick)
app.analyser.add :average_intensity do |temp_object|
  (`python lib/simple_analyser.py #{temp_object.path}`.gsub("\n","").strip.to_f rescue 0.0)
end
app.processor.add :first_frame_of_gif_as_png do |temp_object|
  tempfile = Tempfile.new(['dragonfly','.png'])
  tempfile.binmode
  tempfile.close
  `convert #{temp_object.path}[0] #{tempfile.path}`
  tempfile
end

image.rb

class Image
  include Mongoid::Document
  # Storage
  field :image_aspect_ratio, type: Float
  field :average_intensity, type: Float
  # Index
  index :image_aspect_ratio
  index :average_intensity
  # Hook to do the analysis step
  after_create :set_average_intensity!
  def set_average_intensity!
    # Examples of how to handle SVG/GIF stuff here.
    if self.image_mime_type.downcase.include?("svg")
      self.average_intensity = self.image.png.average_intensity
    elsif self.image_mime_type.downcase.include?("gif")
      self.average_intensity = self.image.process(:first_frame_of_gif_as_png).average_intensity
    else
      self.average_intensity = self.image.average_intensity
    end
    self.save
  end
  def find_duplicates(dist=0.15)
    return Image.where(
      :average_intensity.lt=>(self.average_intensity+dist), :average_intensity.gt=>(self.average_intensity-dist),
      :image_aspect_ratio.lt=>(self.image_aspect_ratio+dist), :image_aspect_ratio.gt=>(self.image_aspect_ratio-dist)
    ).not_in(id: [self.id]).all rescue []
  end
end

simple_analyser.py

from opencv.cv import *
from opencv.highgui import *
from optparse import OptionParser
class Simple2DAnalyser:
  def __init__(self, imagename):
    im = cvLoadImageM(imagename,CV_LOAD_IMAGE_COLOR)
    cvSmooth(im, im, CV_GAUSSIAN, 3)
    sums = cvSum(im)
    self.r = (sums[0]/(im.rows*im.cols))*0.7
    self.g = (sums[1]/(im.rows*im.cols))*1
    self.b = (sums[2]/(im.rows*im.cols))*0.5
  def getValues(self):
    return ((self.b+self.g+self.r)/3)

usage = "usage: %prog filename"
parser = OptionParser(usage=usage)
(options, args) = parser.parse_args()
s = Simple2DAnalyser(args[0])
print s.getValues()