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.



562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
 
# File 'lib/exifr/tiff.rb', line 562

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
  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.



560
561
562
 
# File 'lib/exifr/tiff.rb', line 560

def offset
  @offset
end

#tag ⇒ Object (readonly)

Returns the value of attribute tag.



560
561
562
 
# File 'lib/exifr/tiff.rb', line 560

def tag
  @tag
end

#value ⇒ Object (readonly)

Returns the value of attribute value.



560
561
562
 
# File 'lib/exifr/tiff.rb', line 560

def value
  @value
end