Converting a PDF into multiple images

[Nathan Broadbent]

I've been struggling to do this with Carrierwave. Shrine looks much more flexible, so I've been thinking about switching to Shrine.

How would I go about converting a single PDF into multiple images, with one image per page? The Shrine docs suggest creating a new table for multiple files, but I think that would be overkill in this case. I would like to store an array of images in the metadata, or even just a page count that can be used to generate the URLs.

I've found a few hints, such as the "pdf page count" metadata on this page: http://shrinerb.com/rdoc/classes/Shrine/Plugins/AddMetadata.html

But I don't know where to go from there.

This is the code I was testing for Carrierwave:

version :jpg do

process :convert_to_images

def convert_to_images(*args)

image = MiniMagick::Image.open(current_path)

image.pages.each_with_index do |page, index|

MiniMagick::Tool::Convert.new do |convert|

convert.background 'white'

convert.flatten

convert.density 300

convert.quality 95

convert << page.path

convert << "#{CarrierWave.root}/#{store_dir}/image-#{index}.jpg"

end

end

end

end

(It doesn't work properly, but it does generate the correct images.)

I've looked at the "versions" plugin, but the documentation states that I need to return a hash of files. I really just want to return an array of generated images, and the page count.

Any help would be greatly appreciated! Also a PDF example would be really helpful in the docs.

Thanks,

Nathan

[Janko Marohnić]

At the moment Shrine doesn't support arrays of uploaded files, but you can still achieve the same behaviour with a hash of versions (note that I haven't tested this):

class ImageUploader < Shrine

  plugin :versions

  plugin :processing

  process(:store) do |io, context|

    pdf      = io.download

    versions = {}

    image = MiniMagick::Image.new(pdf.path)

    image.pages.each_with_index do |page, index|

      page_image = Tempfile.new("version-#{index}", binmode: true)

      MiniMagick::Tool::Convert.new do |convert|

        convert.background 'white'

        convert.flatten

        convert.density 300

        convert.quality 95

        convert << page.path

        convert << page_image.path

      end

      page_image.open # refresh updated file

      versions[:"page_#{index + 1}"] = page_image

    end

    versions

  end

end

Assuming you have a "Document" model and you attached a PDF to a "file" attachment field, you can then retrieve an array of pages with Hash#values:

pages = document.file.values

pages #=> [...array of pages...]

pages.count #=> number of pages

I've added it to my TODO list to show this kind of example in the documentation.

Kind regards,

Janko

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[daniba...@gmail.com]

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