Class: EXIFR::TIFF::Field

Inherits:
Object
  • Object
show all
Defined in:
lib/exifr/tiff.rb

Overview

:nodoc:

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(data, pos) ⇒ Field

Returns a new instance of Field.



606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
 
# File 'lib/exifr/tiff.rb', line 606

def initialize(data, pos)
  @tag, count, @offset = data.readshort(pos), data.readlong(pos + 4), data.readlong(pos + 8)
  @type = data.readshort(pos + 2)

  case @type
  when 1 # byte
    len, pack = count, proc { |d| d }
  when 6 # signed byte
    len, pack = count, proc { |d| sign_byte(d) }
  when 2 # ascii
    len, pack = count, proc { |d| d.unpack('Z*') }
  when 3 # short
    len, pack = count * 2, proc { |d| d.unpack(data.short + '*') }
  when 8 # signed short
    len, pack = count * 2, proc { |d| d.unpack(data.short + '*').map{|n| sign_short(n)} }
  when 4 # long
    len, pack = count * 4, proc { |d| d.unpack(data.long + '*') }
  when 9 # signed long
    len, pack = count * 4, proc { |d| d.unpack(data.long + '*').map{|n| sign_long(n)} }
  when 7 # undefined
    # UserComment
    if @tag == 0x9286
      len, pack = count, proc { |d| d.strip }
      len -= 8 # reduce to account for first 8 bytes
      start = len > 4 ? @offset + 8 : (pos + 8) # UserComment first 8-bytes is char code
      @value = [pack[data[start..(start + len - 1)]]].flatten
    end
  when 5 # unsigned rational
    len, pack = count * 8, proc do |d|
      rationals = []
      d.unpack(data.long + '*').each_slice(2) do |f|
        rationals << rational(*f)
      end
      rationals
    end
  when 10 # signed rational
    len, pack = count * 8, proc do |d|
      rationals = []
      d.unpack(data.long + '*').map{|n| sign_long(n)}.each_slice(2) do |f|
        rationals << rational(*f)
      end
      rationals
    end
  when 11 # float
    len, pack = count * 4, proc { |d| d.unpack(data.float + '*') }
  when 12 # double
    len, pack = count * 8, proc { |d| d.unpack(data.double + '*') }
  else
    return
  end

  if len && pack && @type != 7
    start = len > 4 ? @offset : (pos + 8)
    d = data[start..(start + len - 1)]
    @value = d && [pack[d]].flatten
  end
end

Instance Attribute Details

#offset ⇒ Object (readonly)

Returns the value of attribute offset.



604
605
606
 
# File 'lib/exifr/tiff.rb', line 604

def offset
  @offset
end

#tag ⇒ Object (readonly)

Returns the value of attribute tag.



604
605
606
 
# File 'lib/exifr/tiff.rb', line 604

def tag
  @tag
end

#value ⇒ Object (readonly)

Returns the value of attribute value.



604
605
606
 
# File 'lib/exifr/tiff.rb', line 604

def value
  @value
end