Rails - Apr 2006 - ImageMagick and EXIF Data

Hi there,

I''m writing a little application that parses an image file and extracts
the
camera settings from the file (the EXIF data) and saves all the fields to
the database. The idea is that after awhile people will be able to search
based on camera make, model, lens settings, etc... and all the pictures that
meet those requirements will be displayed. The picture is stored on the file
system, and not in the DB. I''m a little lost as to where to actually
perform
the parse on the EXIF data though. I know it should probably be done in the
image model. In my DB I have columns named "camera_model",
"camera_make",
"focal_length", etc... Here''s what I
''think'' I need to do to grab the the
data from the image file:

def load_exif_data(image)
    self.shutter_speed =
image.get_exif_by_entry("ShutterSpeedValue")[0][1]
    self.aperture = image.get_exif_by_entry("ApertureValue")[0][1]
    self.iso_speed = image.get_exif_by_entry("ISOSpeedRatings")[0][1]
    self.camera_model = image.get_exif_by_entry("Model")[0][1]
    self.focal_length = image.get_exif_by_entry("FocalLength")[0][1]
    self.flash = image.get_exif_by_entry("Flash")[0][1]
    self.save
  end

---------------------------------------------

Here''s my whole image model ( it''s a rough model, but it works
for now):

require ''RMagick''

class Image < ActiveRecord::Base

DIRECTORY = ''public/uploaded_images''
THUMBDIRECTORY = ''public/thumbs''
DISPLAY_DIRECTORY = ''/public/uploaded_images/''
DISPLAYTHUMBS_DIRECTORY = ''/public/thumbs/''

after_save :process
after_destroy :cleanup


  def file_data=(file_data)
    @file_data = file_data
    write_attribute ''extension'',
file_data.original_filename.split(''.'').last.downcase
    write_attribute("content_type", file_data.content_type)
    write_attribute("original_name", file_data.original_filename)
    write_attribute("file_size", file_data.size)
  end

  def url
    path.sub(/^public/,'''')
  end

  def to_url
    return  DISPLAYTHUMBS_DIRECTORY + "#{self.id}-thumb.jpg"
  end

  def to_large_url
    return DISPLAY_DIRECTORY + "#{self.id}-full.jpg"
  end

  def thumbnail_url
    thumbnail_path.sub(/^public/,'''')
  end

  def path
    File.join(DIRECTORY, "#{self.id}-full.jpg")
  end

  def thumbnail_path
    File.join(THUMBDIRECTORY, "#{self.id}-thumb.jpg")
  end

  def self.display_all_images
    find(:all, :order   =>    "created_at desc")
  end


  private
  #######

  def process
    if @file_data
      create_directory
      cleanup
      save_fullsize
      create_fullsize
      create_thumbnail
      load_exif_data
      @file_data = nil
    end
  end

  def save_fullsize
    File.open(path,''w'') do |file|
      file.puts @file_data.read
    end
  end

  def create_fullsize
    img = Magick::Image.read(path).first
    img.change_geometry!(''700 x 700'') { |cols, rows, large|
      large.resize!(cols, rows)
      large.write path
    }
  end


  def create_thumbnail
    img = Magick::Image.read(path).first
    img.change_geometry!(''200 x 160'') { |cols, rows,
thumbnail|
      thumbnail.resize!(cols, rows)
      chopped = thumbnail.chop(0, thumbnail.rows/2, thumbnail.columns/2,
thumbnail.rows)
      chopped.write thumbnail_path
    }
  end

  def create_directory
    FileUtils.mkdir_p DIRECTORY
  end

  def cleanup
    Dir[File.join(DIRECTORY, "#{self.id}-*")].each do |filename|
      File.unlink(filename) rescue nil
    end
  end

end
------------------------------------------

How would I actually link my load_exif_data method up to this model?


Thank you,
Dave Hoefler
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