How to retrieve EXIF information of an image in Rails

问题

I am using Rails paperclip for displaying the images in my page. I want to know how to retrieve EXIF information of an image(like dimensions, camera model,height,width., etc).Can any one help me out???

Thanks!!!

回答1:

Did you give exifr gem a try? From the documentation

EXIFR::JPEG.new('IMG_6841.JPG').width               # => 2272
EXIFR::JPEG.new('IMG_6841.JPG').height              # => 1704
EXIFR::JPEG.new('IMG_6841.JPG').exif?               # => true
EXIFR::JPEG.new('IMG_6841.JPG').model               # => "Canon PowerShot G3"
EXIFR::JPEG.new('IMG_6841.JPG').date_time           # => Fri Feb 09 16:48:54 +0100 2007
EXIFR::JPEG.new('IMG_6841.JPG').exposure_time.to_s  # => "1/15"
EXIFR::JPEG.new('IMG_6841.JPG').f_number.to_f       # => 2.0

回答2:

There are 3 gems to do this:

mini_exiftool: ExifTool command-line wrapper
exifr: Pure Ruby
exif: C Extension (by me)

If you want to write or edit EXIF tag, you should choose mini_exiftool, it's more powerful but very slow, as the benchmark shown below, exif is 8 times faster than exifr, and 1200 times than that of mini_exiftool.

benchmark:

require 'benchmark'
require 'mini_exiftool'
require 'exifr'
require 'exif'

N = 50
FILE_PATH = File.expand_path('../../spec/sample.jpg', __FILE__)
Benchmark.bmbm do |x|
  x.report 'mini_exiftool' do
    N.times{ MiniExiftool.new(FILE_PATH).image_width }
  end
  x.report 'exifr' do
    N.times{ EXIFR::JPEG.new(FILE_PATH).width }
  end
  x.report 'exif' do
    N.times{ Exif::Data.new(FILE_PATH).image_width }
  end
end

output:

Rehearsal -------------------------------------------------
mini_exiftool   0.150000   0.050000  12.390000 ( 12.546417)
exifr           0.090000   0.000000   0.090000 (  0.091090)
exif            0.010000   0.000000   0.010000 (  0.010343)
--------------------------------------- total: 12.490000sec
                    user     system      total        real
mini_exiftool   0.150000   0.050000  12.400000 ( 12.540122)
exifr           0.080000   0.000000   0.080000 (  0.083251)
exif            0.010000   0.000000   0.010000 (  0.009855)

mini_exiftool is a bit overkill to only retrieve data. So in your case, I think you should use exifr in JRuby, or give exif a try in MRI.

回答3:

You might try the mini_exiftool gem, a wrapper for the exiftool command-line tool.

While the gem requires you to actually install the command-line tool, the result is that you get a lot more power. Compared to exifr, which only gives you support for JPG and TIF files, exiftool supports a huge number of file formats. It also supports reading and writing of exif data, whereas exifr only supports reading.

回答4:

after_photo_post_process :copy_exif_data 
  private 
  def copy_exif_data 
    exif =EXIFR::JPEG.new(photo.queued_for_write[:original]) 
    self.exif_value = exif
  end

This is working code which i am used.

来源：https://stackoverflow.com/questions/11839664/how-to-retrieve-exif-information-of-an-image-in-rails

标签

ruby-on-rails

ruby

paperclip

exif