Class: SwfConverter::Engine::Alphize::Blender

Inherits:
Object
  • Object
show all
Includes:
Runner
Defined in:
lib/swf_converter/engine/alphize/blender.rb

Instance Method Summary collapse

Methods included from Runner

#e, #run

Constructor Details

#initialize(images) ⇒ Blender

Returns a new instance of Blender.



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# File 'lib/swf_converter/engine/alphize/blender.rb', line 11

def initialize(images)
  @originals = images
end

Instance Method Details

#blend!(output_path) ⇒ Object 



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# File 'lib/swf_converter/engine/alphize/blender.rb', line 15

def blend!(output_path)
  # The strategy here is based on the following principle:
  # original_image.alpha == (CHANNEL_MAX - image_on_white.red) + image_on_black.red
  # (Applies to blue and green, too. Derived from the formulas applied
  # by the original composition; not too hard to work out.)
  # So, we will first get a grayscale version of an alpha mask by
  # negating the image-on-white (create_negative!), then add it to the
  # image-on-black to get the grayscale alpha mask (create_alpha!).
  # The alpha mask image has white where the original image is opaque,
  # and black where it is fully transparent, and gray where it is
  # partially transparent. Once we have that image, since the RGB
  # values in image-on-black were found by multiplying by the alpha
  # value, we divide image-on-black by the grayscale alpha mask to get
  # an opaque version of the image with the correct colors
  # (create_division!), then apply that grayscale image as an alpha
  # mask to save the final image (create_final!).
  with_temps do |temps|
    create_negative!(temps)
    create_alpha!(temps)
    create_division!(temps)
    create_final!(output_path, temps)
  end
end