Method: Origami::Filter::LZW#encode

Defined in:
lib/origami/filters/lzw.rb

#encode(string) ⇒ Object

Encodes given data using LZW compression method.

stream

The data to encode.



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# File 'lib/origami/filters/lzw.rb', line 67

def encode(string)
  if @params.Predictor.is_a?(Integer)
    colors  = @params.Colors.is_a?(Integer) ?  @params.Colors.to_i : 1
    bpc     = @params.BitsPerComponent.is_a?(Integer) ? @params.BitsPerComponent.to_i : 8
    columns = @params.Columns.is_a?(Integer) ? @params.Columns.to_i : 1

    string = Predictor.do_pre_prediction(string, @params.Predictor.to_i, colors, bpc, columns)
  end       
  
  codesize = 9
  result = Utils::BitWriter.new
  result.write(CLEARTABLE, codesize)
  table = clear({})
  
  s = ''        
  string.each_byte do |byte|
    char = byte.chr
    
    case table.size
      when 512 then codesize = 10
      when 1024 then codesize = 11
      when 2048 then codesize = 12
      when 4096
        result.write(CLEARTABLE, codesize)
        codesize = 9
        clear table
        redo
    end
   
    it = s + char
    if table.has_key?(it)
      s = it
    else
      result.write(table[s], codesize)
      table[it] = table.size
      s = char
    end
  end
   
  result.write(table[s], codesize)
  result.write(EOD, codesize)
  
  result.final.to_s
end