Module: Pdfrb::ImageLoader::PNG

Defined in:
lib/pdfrb/image_loader/png.rb

Class Method Summary collapse

Class Method Details

.call(document, data, **_opts) ⇒ Object 



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# File 'lib/pdfrb/image_loader/png.rb', line 8

def call(document, data, **_opts)
  data = data.read if data.is_a?(IO) || data.is_a?(StringIO)
  info = parse_header(data)
  return nil if info.empty?

  image = document.add(
    {
      Type: :XObject,
      Subtype: :Image,
      Width: info[:width],
      Height: info[:height],
      ColorSpace: info[:color_space],
      BitsPerComponent: info[:bits],
      Filter: :FlateDecode,
      DecodeParms: { Predictor: 15, Columns: info[:width] },
      Length: 0,
    },
    type: Pdfrb::Model::Type::XObjectImage
  )
  image.stream = ""
  image
end

.parse_header(data) ⇒ Object 



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# File 'lib/pdfrb/image_loader/png.rb', line 31

def parse_header(data)
  return {} unless data.is_a?(String) && data.bytesize >= 24
  return {} unless data.start_with?("\x89PNG\r\n\x1A\n".b)
  return {} unless data.bytes[12, 4].pack("C*") == "IHDR"

  off = 16
  {
    width: read_u32(data, off),
    height: read_u32(data, off + 4),
    bits: data.getbyte(off + 8),
    color_type: data.getbyte(off + 9),
    color_space: case data.getbyte(off + 9)
                 when 0, 4 then :DeviceGray
                 when 2, 6 then :DeviceRGB
                 when 3 then :Indexed
                 else :DeviceRGB
                 end,
  }
end

.read_u32(data, off) ⇒ Object 



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# File 'lib/pdfrb/image_loader/png.rb', line 51

def read_u32(data, off)
  (data.getbyte(off) << 24) | (data.getbyte(off + 1) << 16) | (data.getbyte(off + 2) << 8) | data.getbyte(off + 3)
end