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Daniel Doubrovkine

aka dB., CTO at artsy.net, fun at playplay.io, NYC

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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.

class ArtworkUploader < CarrierWave::Uploader::Base
version :best do
process :convert => 'jpg'
end
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.

class ArtworkUploader < CarrierWave::Uploader::Base
include CarrierWave::RMagick

version :best do
process :convert => 'jpg'
process :get_geometry

def geometry
@geometry
end
end

def get_geometry
if (@file)
img = ::Magick::Image::read(@file.file).first
@geometry = [img.columns, img.rows]
end
end
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.

class Image

field :best_width
field :best_height

before_save :saving

def saving
geometry = self.image.best.geometry
if (! geometry.nil?)
self.best_width = geometry[0]
self.best_height = geometry[1]
end
end

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?