I recently needed to find out the geometry of the image being uploaded via Carrierwave. Images come in many different sizes and shapes. What I want is to have a “best” image and store its actual size along with my image model.

Define a Best Image

First, lets define a “best” version of the image. That’s one that’s not being resized, only converted into JPG.

1. class ArtworkUploader < CarrierWave::Uploader::Base
2.   version :best do
3.     process :convert => 'jpg'
4.   end
5. end

Fetch Geometry on Upload

Notice the process declarations above: both resize_to_limit and convert are methods of the uploader class. We can therefore add a new get_geometry function and store the geometry of the uploaded image with this version.

1. class ArtworkUploader < CarrierWave::Uploader::Base
2.   include CarrierWave::RMagick
3.  
4.   version :best do
5.     process :convert => 'jpg'
6.     process :get_geometry
7.     
8.     def geometry
9.       @geometry
10.     end
11.   end
12.   
13.   def get_geometry
14.     if (@file)
15.       img = ::Magick::Image::read(@file.file).first
16.       @geometry = [ img.columns, img.rows ]
17.     end
18.   end
19. end

Save Geometry

Finally, we would like to store best_width and best_height with the Image model. We use MongoId, so we can fetch the geometry before_save.

1. class Image
2.   
3.   field :best_width
4.   field :best_height
5.  
6.   before_save :saving
7.  
8.   def saving
9.     geometry = self.image.best.geometry
10.     if (! geometry.nil?)
11.       self.best_width = geometry[0]
12.       self.best_height = geometry[1]
13.     end
14.   end  
15.  
16. end

I think image geometry should be a built-in function and property of Carrierwave. Maybe this can be improved further and make it into the library?