From: Jeremy Hinegardner <jeremy@...>
Date: 2007-05-12T14:35:20+09:00
Subject: Re: EXIF Library

On Sat, May 12, 2007 at 11:44:53AM +0900, 12 34 wrote:
> Newbie here. What's the syntax to read say the date and time the picture 
> was taken?
> 
> I tried:
> 
> puts EXIFR::JPEG.new("/file/is/here/tests/data/exif.jpg").date_time
> 
> and got: NameError: uninitialized constant EXIFR
> 
> Maybe I didn't get it installed right?

Install exifr with : sudo gem install exifr

Example program to display exif tags.

    > cat exif-test.rb
    require 'rubygems'
    require 'exifr'

    image_file = ARGV.first
    exif_info = nil
    case image_file.downcase
    when /.jpg\Z/
        exif_info = EXIFR::JPEG.new(image_file)
    when /.tiff?\Z/
        exif_info = EXIFR::TIFF.new(image_file)
    end

    puts "Standard items".center(72)
    puts "=" * 72
    puts "                          File : #{image_file}"
    puts "                        Height : #{exif_info.height}"
    puts "                         Width : #{exif_info.width}"
    puts

    if exif_info.exif? then
        puts "EXIF information".center(72)
        puts "=" * 72
        h = exif_info.exif.to_hash
        h.each_pair do |k,v|
            puts "#{k.to_s.rjust(30)} : #{v}"
        end
    else
        puts "No EXIF information in this image"
    end 

Running that program on an image

    > ruby exif-test.rb 2004120087.JPG
                                    Standard items                             
    ========================================================================
                              File : 2004120087.JPG
                            Height : 1200
                             Width : 1600

                                EXIF information                            
    ========================================================================
                     exposure_mode : 1
               shutter_speed_value : 117/16
                     exposure_time : 1/160
                       orientation : EXIFR::TIFF::TopLeftOrientation
                    sensing_method : 2
                       color_space : 1
                     metering_mode : 2
                      x_resolution : 180
                     white_balance : 0
          focal_plane_x_resolution : 100000/13
                    aperture_value : 95/32
                          f_number : 14/5
                 pixel_x_dimension : 1600
                date_time_original : Thu Dec 30 12:02:53 -0700 2004
                      y_resolution : 180
                   resolution_unit : 2
                digital_zoom_ratio : 1
          focal_plane_y_resolution : 100000/13
                ycb_cr_positioning : 1
                 pixel_y_dimension : 1200
                             flash : 16
               date_time_digitized : Thu Dec 30 12:02:53 -0700 2004
                              make : Canon
       focal_plane_resolution_unit : 2
               exposure_bias_value : 4294967291/3
                      focal_length : 173/32
                             model : Canon PowerShot SD100
                scene_capture_type : 0
                max_aperture_value : 95/32
                   custom_rendered : 0
         compressed_bits_per_pixel : 3
                         date_time : Thu Dec 30 12:02:53 -0700 2004
enjoy,

-jeremy      

-- 
========================================================================
 Jeremy Hinegardner                              jeremy@hinegardner.org