Carrierwave and mini_magick finding widths & height

Question

After a bit of investigation I decided to use Carrierwave and mini_magick on my new rail3 app.

I\'ve set it up and it works perfectly. However I have a one question. I\

Answer 1

I think the best way is to store the image dimensions in the model (database).

In my case, the model name is attachment. Then I created a migration:

rails g migration add_dimensions_to_attachments image_width:integer image_height:integer

After that, run the migration:

rake db:migrate

In my Image Uploader file app/uploaders/image_uploader.rb, I have:

class ImageUploader < CarrierWave::Uploader::Base

    include CarrierWave::MiniMagick

    process :store_dimensions

    private

    def store_dimensions
      if file && model
        model.image_width, model.image_height = ::MiniMagick::Image.open(file.file)[:dimensions]
      end
    end
  end

With this, the image dimensions is saved in the upload step.

To get the dimensions, I simply run attachment.image_width or attachment.image_height

See the reference here.

Answer 2

Disadvantage of calculating Image height / width using RMagick or MiniMagick in run time:

• Its CPU intensive
• It requires Internet to get image and calculate the dimensions.
• Its a slow process

FYI You can also calculate the Image Height, Width after the Image is fully loaded by using the load event associated with the <img> tag with the help of jQuery.

For Example:

$(document).ready(function(){   
   var $image = $('.fixed-frame img');
   $image.load(function(){
      rePositionLogo($image);
   });

  if($image.prop('complete')){
    rePositionLogo($image);
  }

});

function rePositionLogo($image){
  var height = $image.height();
  var width = $image.width();
  if (width > height) {
    $image.parents('.header').addClass('landscape');
    var marginTop = (105 - $image.height())/2;
    $image.css('margin-top', marginTop + 'px')
  }else{
    $image.parents('.header').addClass('portrait');
  }
}

Be careful, because load() will not trigger when an image is already loaded. This can happens easily when an image is in the user's browser cache.

You can check if an image is already loaded using $('#myImage').prop('complete'), which returns true when an image is loaded.

Answer 3

class Attachment
  mount_uploader :file, FileUploader

  def image
    @image ||= MiniMagick::Image.open(file.path)
  end
end

And use it like this:

Attachment.first.image['width'] # => 400
Attachment.first.image['height'] # => 300

Answer 4

Just for record, I have used a similar solution, however using files with Mongo GridFS, here it goes:

  def image
    @image ||= MiniMagick::Image.read(Mongo::GridFileSystem.new(Mongoid.database).open(file.path, 'r'))
  end