Class: Prawn::Images::JPG

Inherits:
Object
  • Object
show all
Defined in:
lib/prawn/images/jpg.rb

Overview

A convenience class that wraps the logic for extracting the parts of a JPG image that we need to embed them in a PDF

Constant Summary collapse

JPEG_SOF_BLOCKS = 
%W(\xc0 \xc1 \xc2 \xc3 \xc5 \xc6 \xc7 \xc9 \xca \xcb \xcd \xce \xcf)
JPEG_APP_BLOCKS = 
%W(\xe0 \xe1 \xe2 \xe3 \xe4 \xe5 \xe6 \xe7 \xe8 \xe9 \xea \xeb \xec \xed \xee \xef)

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(data) ⇒ JPG

Process a new JPG image

:data

A binary string of JPEG data



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# File 'lib/prawn/images/jpg.rb', line 27

def initialize(data)
  data = StringIO.new(data.dup)

  c_marker = "\xff" # Section marker.
  data.read(2)   # Skip the first two bytes of JPEG identifier.
  loop do
    marker, code, length = data.read(4).unpack('aan')
    raise "JPEG marker not found!" if marker != c_marker

    if JPEG_SOF_BLOCKS.include?(code)
      @bits, @height, @width, @channels = data.read(6).unpack("CnnC")
      break
    end

    buffer = data.read(length - 2)
  end
end

Instance Attribute Details

#bits ⇒ Object (readonly)

Returns the value of attribute bits.



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# File 'lib/prawn/images/jpg.rb', line 17

def bits
  @bits
end

#channels ⇒ Object (readonly)

Returns the value of attribute channels.



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# File 'lib/prawn/images/jpg.rb', line 17

def channels
  @channels
end

#height ⇒ Object (readonly)

Returns the value of attribute height.



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# File 'lib/prawn/images/jpg.rb', line 17

def height
  @height
end

#scaled_height ⇒ Object

Returns the value of attribute scaled_height.



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# File 'lib/prawn/images/jpg.rb', line 18

def scaled_height
  @scaled_height
end

#scaled_width ⇒ Object

Returns the value of attribute scaled_width.



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# File 'lib/prawn/images/jpg.rb', line 18

def scaled_width
  @scaled_width
end

#width ⇒ Object (readonly)

Returns the value of attribute width.



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# File 'lib/prawn/images/jpg.rb', line 17

def width
  @width
end