Module: EideticPDF::JpegInfo

Included in:
PageWriter
Defined in:
lib/epdfs.rb

Overview

:nodoc:

Class Method Summary collapse

Class Method Details

.jpeg?(image) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/epdfs.rb', line 77

def jpeg?(image)
  # image[0, 2] == "\xFF\xD8"
  # image[0, 2].hash == "\xFF\xD8".hash
  # String#bytes requires Ruby 1.8.7+
  image.bytes.first(2) == [0xFF, 0xD8]
end

.jpeg_dimensions(image) ⇒ Object

Raises:

  • (ArgumentError) 


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# File 'lib/epdfs.rb', line 84

def jpeg_dimensions(image)
  raise ArgumentError, "Not a JPEG" unless jpeg?(image)
  image = image.dup
  image.slice!(0, 2) # delete jpeg marker
  while marker = image.slice!(0, 4)
    m, c, l = marker.unpack('aan')
    raise "Bad JPEG" unless m == "\xFF"
    if ["\xC0", "\xC1", "\xC2", "\xC3", "\xC5", "\xC6", "\xC7", "\xC9", "\xCA", "\xCB", "\xCD", "\xCE", "\xCF"].include?(c)
      dims = image.slice(0, 6)
      bits_per_component, height, width, components = dims.unpack('CnnC')
      break
    end
    image.slice!(0, l - 2)
  end
  [width, height, components, bits_per_component]
end