Module: Origami::Filter::Predictor

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

Constant Summary collapse

NONE = 
1
TIFF = 
2
PNG_NONE = 
10
PNG_SUB = 
11
PNG_UP = 
12
PNG_AVERAGE = 
13
PNG_PAETH = 
14
PNG_OPTIMUM = 
15

Class Method Summary collapse

Class Method Details

.do_png_post_prediction(data, bpp, bpr) ⇒ Object 



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# File 'lib/origami/filters/predictors.rb', line 108

def self.do_png_post_prediction(data, bpp, bpr)

  result = ""
  uprow = "\0" * bpr
  thisrow = "\0" * bpr
  nrows = (data.size + bpr - 1) / bpr
  
  nrows.times do |irow|

    line = data[irow * bpr, bpr]
    predictor = 10 + line[0].ord
    line[0] = "\0"

    for i in (1..line.size-1)
      up = uprow[i].ord

      if bpp > i
        left = upleft = 0
      else
        left = line[i-bpp].ord
        upleft = uprow[i-bpp].ord
      end

      case predictor
        when PNG_NONE
          thisrow = line 
        when PNG_SUB
          thisrow[i] = ((line[i].ord + left) & 0xFF).chr
        when PNG_UP
          thisrow[i] = ((line[i].ord + up) & 0xFF).chr
        when PNG_AVERAGE
          thisrow[i] = ((line[i].ord + ((left + up) / 2)) & 0xFF).chr
        when PNG_PAETH
          p = left + up - upleft
          pa, pb, pc = (p - left).abs, (p - up).abs, (p - upleft).abs

          thisrow[i] = ((line[i].ord + 
            case [ pa, pb, pc ].min
              when pa then left
              when pb then up
              when pc then upleft
            end
          ) & 0xFF).chr
      else
        puts "Unknown PNG predictor : #{predictor}"
        thisrow = line
      end
      
    end

    result << thisrow[1..-1]
    uprow = thisrow
  end
  
  result
end

.do_png_pre_prediction(data, predictor, bpp, bpr) ⇒ Object 



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# File 'lib/origami/filters/predictors.rb', line 165

def self.do_png_pre_prediction(data, predictor, bpp, bpr)
  
  result = ""
  nrows = data.size / bpr

  line = "\0" + data[-bpr, bpr]
  
  (nrows-1).downto(0) do |irow|

    uprow = 
    if irow == 0 
      "\0" * (bpr+1) 
    else 
      "\0" + data[(irow-1)*bpr,bpr]
    end

    bpr.downto(1) do |i|

      up = uprow[i].ord
      left = line[i-bpp].ord
      upleft = uprow[i-bpp].ord

      case predictor
        when PNG_SUB
          line[i] = ((line[i].ord - left) & 0xFF).chr
        when PNG_UP
          line[i] = ((line[i].ord - up) & 0xFF).chr
        when PNG_AVERAGE
          line[i] = ((line[i].ord - ((left + up) / 2)) & 0xFF).chr
        when PNG_PAETH
          p = left + up - upleft
          pa, pb, pc = (p - left).abs, (p - up).abs, (p - upleft).abs

          line[i] = ((line[i].ord - 
          case [ pa, pb, pc ].min
            when pa then left
            when pb then up
            when pc then upleft
          end
          ) & 0xFF).chr
        when PNG_NONE
      else
        raise PredictorError, "Unsupported PNG predictor : #{predictor}"
      end
      
    end
    
    line[0] = (predictor - 10).chr
    result = line + result
    
    line = uprow
  end
  
  result
end

.do_post_prediction(data, predictor = NONE, colors = 1, bpc = 8, columns = 1) ⇒ Object 



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# File 'lib/origami/filters/predictors.rb', line 78

def self.do_post_prediction(data, predictor = NONE, colors = 1, bpc = 8, columns = 1)

  return data if predictor == NONE

  unless (1..4) === colors
    raise PredictorError, "Colors must be between 1 and 4"
  end

  unless [1,2,4,8,16].include?(bpc)
    raise PredictorError, "BitsPerComponent must be in 1, 2, 4, 8 or 16"
  end

  # components per line
  nvals = columns * colors

  # bytes per pixel
  bpp = (colors * bpc + 7) >> 3

  # bytes per row
  bpr = ((nvals * bpc + 7) >> 3) + 1

  if predictor == TIFF
    do_tiff_post_prediction(data, colors, bpc, columns)
  elsif predictor >= 10 # PNG
    do_png_post_prediction(data, bpp, bpr)
  else
    raise PredictorError, "Unknown predictor : #{predictor}"
  end
end

.do_pre_prediction(data, predictor = NONE, colors = 1, bpc = 8, columns = 1) ⇒ Object 



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# File 'lib/origami/filters/predictors.rb', line 44

def self.do_pre_prediction(data, predictor = NONE, colors = 1, bpc = 8, columns = 1)
 
   return data if predictor == NONE

   unless (1..4) === colors.to_i
     raise PredictorError, "Colors must be between 1 and 4"
   end

   unless [1,2,4,8,16].include?(bpc.to_i)
     raise PredictorError, "BitsPerComponent must be in 1, 2, 4, 8 or 16"
   end

   # components per line
   nvals = columns * colors

   # bytes per pixel
   bpp = (colors * bpc + 7) >> 3

   # bytes per row
   bpr = (nvals * bpc + 7) >> 3

   unless data.size % bpr == 0
     raise PredictorError, "Invalid data size #{data.size}, should be multiple of bpr=#{bpr}"
   end

   if predictor == TIFF
     do_tiff_pre_prediction(data, colors, bpc, columns)
   elsif predictor >= 10 # PNG
     do_png_pre_prediction(data, predictor, bpp, bpr)
   else
     raise PredictorError, "Unknown predictor : #{predictor}"
   end
end

.do_tiff_post_prediction(data, colors, bpc, columns) ⇒ Object

:nodoc:



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# File 'lib/origami/filters/predictors.rb', line 221

def self.do_tiff_post_prediction(data, colors, bpc, columns) #:nodoc:

  bpr = (colors * bpc * columns + 7) >> 3
  nrows = data.size / bpr
  bitmask = (1 << bpc) - 1
  result = Utils::BitWriter.new

  nrows.times do |irow|
    line = Utils::BitReader.new(data[irow * bpr, bpr])

    pixel = ::Array.new(colors, 0)
    columns.times do
      diffpixel = ::Array.new(colors) { line.read(bpc) }
      pixel = pixel.zip(diffpixel).map!{|c, diff| (c + diff) & bitmask}
      
      pixel.each do |c|
        result.write(c, bpc)
      end
    end
    
    result.final
  end

  result.final.to_s
end

.do_tiff_pre_prediction(data, colors, bpc, columns) ⇒ Object

:nodoc:



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# File 'lib/origami/filters/predictors.rb', line 247

def self.do_tiff_pre_prediction(data, colors, bpc, columns) #:nodoc:

  bpr = (colors * bpc * columns + 7) >> 3
  nrows = data.size / bpr
  bitmask = (1 << bpc) - 1
  result = Utils::BitWriter.new

  nrows.times do |irow|
    line = Utils::BitReader.new(data[irow * bpr, bpr])

    diffpixel = ::Array.new(colors, 0)
    columns.times do
      pixel = ::Array.new(colors) { line.read(bpc) }
      diffpixel = diffpixel.zip(pixel).map!{|diff, c| (c - diff) & bitmask}
      
      diffpixel.each do |c|
        result.write(c, bpc)
      end
    end
    
    result.final
  end
 
  result.final.to_s
end