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.



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# File 'lib/exifr/tiff.rb', line 550

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
  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.



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# File 'lib/exifr/tiff.rb', line 548

def offset
  @offset
end

#tag ⇒ Object (readonly)

Returns the value of attribute tag.



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# File 'lib/exifr/tiff.rb', line 548

def tag
  @tag
end

#value ⇒ Object (readonly)

Returns the value of attribute value.



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# File 'lib/exifr/tiff.rb', line 548

def value
  @value
end