no way to select frames when using ImageMagick converters

[k3rni]

Frames (as in a GIF, MNG animation or a PS, PDF file with multiple pages) are selected using a subscript notation (see http://www.imagemagick.org/script/command-line-processing.php, under "Selecting Frames"). When not selected, IM either keeps the multiple-image format, or produces multiple separate files.

Dragonfly currently doesn't offer an option to choose which frame I want to work on.

Examples:

convert multipage.pdf -thumbnail 100x100 outputfile

creates outputfile as a multipage pdf, each page scaled down appropriately

convert multipage.pdf -thumbnail 100x100 outputfile.png

produces as many files named outputfile-%d.png as there were pages

convert multipage.pdf[0] -thumbnail 100x100 outputfile

creates a single-page pdf, scaled down

convert multipage.pdf[0] -thumbnail 100x100 outputfile.png

creates a single png file, with the desired thumbnail

The last option is what I'm after, such as: Dragonfly[:app].fetch(UID).convert('-thumbnail 100x100', :frame => 0).png or Dragonfly[:app].fetch(UID).thumb('100x100', :frame => 0).png

Or have I missed something in the docs?

[k3rni]

Also, for PDFs at least, page numbering doesn't have to start at 0. But that's not really important here.

[markevans]

I see. you're correct - it's not particularly supported yet because the imagemagick processors use a "convert" method under the covers which obscures the path argument and doesn't allow adding a number [n] I'll add this to the TODO list, or submit a pull request if you wish (though be warned I'm changing the processors fairly drastically in a branch soon be merged in)

[aaronchi]

was support ever added for this? Trying to resize only the first frame of an animated gif

[markevans]

this has been added in version 1 http://markevans.github.io/dragonfly/imagemagick/#processors

[aaronchi]

I saw. New version look great :)

The other thing I had added to dragonfly was a frame counter to analyzers to see if an image is animated. Not sure if you want to add this to the default analyzer but this is the code I added to count frames

# Counts frames to see if an image is animated
module Dragonfly
  module ImageMagick
    module Analysers
      class ImageAnimated

        def call(content)
          identify_command = content.env[:identify_command] || 'identify'
          details = content.shell_eval do |path|
            "#{identify_command} -format '%n' #{path}"
          end
          details.scan(/\d/).join('').to_i > 1
        end

      end
    end
  end
end

[markevans]

cool! good to see the new custom analyser stuff getting used. I won't add it by default if you don't mind, as I'm trying to keep the codebase small and let users do their own processors/analysers as much as possible. by the way there's also a method "identify" (not an analyser) and a configuration option "define" so if you don't need it to be an analyser, you can just do this now in the config:

define :image_animated? do
  identify("-format %n").to_i > 1
end

[k3rni]

:+1: nicely done.