Module: HexaPDF::ImageLoader::JPEG

Defined in:
lib/hexapdf/image_loader/jpeg.rb

Overview

This module is used for loading images in the JPEG format from files or IO streams.

See: PDF2.0 s7.4.8, ITU T.81 Annex B, ITU T.872

Constant Summary collapse

MAGIC_FILE_MARKER =

The magic marker that tells us if the file/IO contains an image in JPEG format.

"\xFF\xD8\xFF".b
SOF_MARKERS =

The various start-of-frame markers that tell us which kind of JPEG it is. The marker segment itself contains all the needed information needed for creating the PDF image object.

See: ITU T.81 B1.1.3

[
  0xC0, 0xC1, 0xC2, 0xC3, 0xC5, 0xC6, 0xC7, 0xC9, 0xCA, 0xCB, 0xCD, 0xCE, 0xCF
].freeze
APP14_MARKER =

Adobe uses the marker 0xEE (APPE or APP14) for its purposes. We need to use it for determinig whether we have a CMYK or YCCK image.

0xEE
APP14_TRANSFORM_CMYK =

Value of the 12th byte in an APP14 marker specifying that the image uses CMYK color encoding, with all four colors complemented.

0
EOI_MARKER =

End-of-image marker

0xD9
SOS_MARKER =

Start-of-scan marker

0xDA

Class Method Summary collapse

Class Method Details

.handles?(file_or_io) ⇒ Boolean

:call-seq:

JPEG.handles?(filename)     -> true or false
JPGE.handles?(io)           -> true or false

Returns true if the given file or IO stream can be handled, ie. if it contains an image in JPEG format.



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# File 'lib/hexapdf/image_loader/jpeg.rb', line 79

def self.handles?(file_or_io)
  if file_or_io.kind_of?(String)
    File.read(file_or_io, 3, mode: 'rb') == MAGIC_FILE_MARKER
  else
    file_or_io.rewind
    file_or_io.read(3) == MAGIC_FILE_MARKER
  end
end

.load(document, file_or_io) ⇒ Object

:call-seq:

JPEG.load(document, filename)    -> image_obj
JPEG.load(document, io)          -> image_obj

Creates a PDF image object from the JPEG file or IO stream.



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# File 'lib/hexapdf/image_loader/jpeg.rb', line 93

def self.load(document, file_or_io)
  dict = if file_or_io.kind_of?(String)
           File.open(file_or_io, 'rb') {|io| image_data_from_io(io) }
         else
           image_data_from_io(file_or_io)
         end
  document.add(dict, stream: HexaPDF::StreamData.new(file_or_io))
end