Class: ZIMG::JPEG::Decoder

Inherits:
Object
  • Object
show all
Defined in:
lib/zimg/jpeg/decoder.rb

Instance Method Summary collapse

Constructor Details

#initialize(data, frame, components, reset_interval, spectral_start, spectral_end, ah, al) ⇒ Decoder

rubocop:disable Metrics/ParameterLists



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# File 'lib/zimg/jpeg/decoder.rb', line 229

def initialize(data, frame, components, reset_interval, spectral_start, spectral_end, ah, al)
  @components       = components
  @reset_interval   = reset_interval
  @spectral_end     = spectral_end
  @spectral_start   = spectral_start
  @al = al
  @ah = ah

  @mcus_per_line    = frame.mcus_per_line
  @mcus_per_column  = frame.mcus_per_column
  @progressive      = frame.progressive

  @offset = 0
  @bit_io = BitEnumerator.new(data)
end

Instance Method Details

#decode_baseline(component, dst) ⇒ Object 



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# File 'lib/zimg/jpeg/decoder.rb', line 357

def decode_baseline(component, dst)
  t = component.huffman_table_dc.decode(@bit_io)
  diff = t == 0 ? 0 : @bit_io.receive_extend(t)
  dst[0] = (component.pred += diff)
  k = 1
  while k < 64
    rs = component.huffman_table_ac.decode(@bit_io)
    s = rs & 15
    r = rs >> 4
    if s == 0
      break if r < 15

      k += 16
      next
    end
    k += r
    z = DCT_ZIGZAG[k]
    dst[z] = @bit_io.receive_extend(s)
    k += 1
  end
end

#decode_block(component, decode_fn, mcu) ⇒ Object 



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# File 'lib/zimg/jpeg/decoder.rb', line 342

def decode_block(component, decode_fn, mcu)
  block_row = mcu / component.blocks_per_line
  block_col = mcu % component.blocks_per_line

  if @bit_io.eof?
    # If we've run out of data, just leave the MCU set to zeroes.
    # This way, we return uniform gray for the remainder of the segment.
  else
    decode_fn.call(component, component.blocks[block_row][block_col])
  end
rescue StopIteration
  # catch unexpected end of data (partial_progressive.jpg, non-interleaved_progressive-*.jpg)
  warn "[?] unexpected EOF"
end

#decode_mcu(component, decode_fn, mcu, row, col) ⇒ Object 



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# File 'lib/zimg/jpeg/decoder.rb', line 326

def decode_mcu(component, decode_fn, mcu, row, col)
  # If we've run out of data, just leave the MCU set to zeroes.
  # This way, we return uniform gray for the remainder of the segment.
  return if @bit_io.eof?

  mcu_row = mcu / @mcus_per_line
  mcu_col = mcu % @mcus_per_line
  block_row = mcu_row * component.v + row
  block_col = mcu_col * component.h + col

  decode_fn.call(component, component.blocks[block_row][block_col])
rescue StopIteration
  # catch unexpected end of data (partial_progressive.jpg, non-interleaved_progressive-*.jpg)
  warn "[?] unexpected EOF"
end

#decode_mcu_AC_first(component, dst) ⇒ Object 



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# File 'lib/zimg/jpeg/decoder.rb', line 379

def decode_mcu_AC_first(component, dst)
  if @eobrun > 0
    @eobrun -= 1
    return
  end
  k = @spectral_start
  e = @spectral_end
  while k <= e
    break unless (rs = component.huffman_table_ac.decode(@bit_io))

    s = rs & 15
    r = rs >> 4
    if s == 0
      if r < 15
        @eobrun = @bit_io.receive(r) + (1 << r) - 1
        break
      end
      # r == 15
      k += 16
      next
    end
    # s > 0
    k += r
    z = DCT_ZIGZAG[k]
    dst[z] = @bit_io.receive_extend(s) * (1 << @al)
    k += 1
  end
end

#decode_mcu_AC_refine(component, dst) ⇒ Object 



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# File 'lib/zimg/jpeg/decoder.rb', line 408

def decode_mcu_AC_refine(component, dst)
  next_value = nil
  k = @spectral_start
  e = @spectral_end
  r = 0
  z = 0
  while k <= e
    z = DCT_ZIGZAG[k]
    direction = dst[z] < 0 ? -1 : 1
    case @successive_ac_state
    when 0 # initial state
      rs = component.huffman_table_ac.decode(@bit_io)
      s = rs & 15
      r = rs >> 4
      case s
      when 0
        if r < 15
          @eobrun = @bit_io.receive(r) + (1 << r)
          @successive_ac_state = 4
        else
          r = 16
          @successive_ac_state = 1
        end
      when 1
        next_value = @bit_io.receive_extend(1)
        @successive_ac_state = r == 0 ? 3 : 2
      else
        raise "invalid ACn encoding" # libjpeg-turbo: "Corrupt JPEG data: bad Huffman code"
      end
      next
    when 1, 2 # skipping r zero items
      if dst[z] != 0
        dst[z] += (@bit_io.next << @al) * direction
      else
        r -= 1
        if r == 0
          @successive_ac_state = @successive_ac_state == 2 ? 3 : 0
        end
      end
    when 3 # set value for a zero item
      if dst[z] != 0
        dst[z] += (@bit_io.next << @al) * direction
      else
        dst[z] = next_value << @al
        @successive_ac_state = 0
      end
    when 4 # eob
      dst[z] += (@bit_io.next << @al) * direction if dst[z] != 0
    else
      raise "invalid AC state #{@successive_ac_state}"
    end # case
    k += 1
  end # while

  # corresponds to "Output newly nonzero coefficient" line of jdphuff.c
  # (samples/jpeg/jpeg-decoder/tests/reftest/images/partial_progressive.jpg)
  if @successive_ac_state == 3 && next_value && z < 64
    dst[z] = next_value << @al
    next_value = nil
  end

  return unless @successive_ac_state == 4

  @eobrun -= 1
  @successive_ac_state = 0 if @eobrun == 0
end

#decode_mcu_DC_first(component, dst) ⇒ Object 



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# File 'lib/zimg/jpeg/decoder.rb', line 475

def decode_mcu_DC_first(component, dst)
  t = component.huffman_table_dc.decode(@bit_io)
  diff = t == 0 ? 0 : (@bit_io.receive_extend(t) << @al)
  dst[0] = (component.pred += diff)
end

#decode_mcu_DC_refine(_component, dst) ⇒ Object 



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# File 'lib/zimg/jpeg/decoder.rb', line 481

def decode_mcu_DC_refine(_component, dst)
  dst[0] |= (@bit_io.next << @al)
end

#decode_scan ⇒ Object

rubocop:enable Metrics/ParameterLists



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# File 'lib/zimg/jpeg/decoder.rb', line 246

def decode_scan
  @successive_ac_state = 0

  decode_fn =
    if @progressive
      if @spectral_start == 0
        @ah == 0 ? :decode_mcu_DC_first : :decode_mcu_DC_refine
      else
        @ah == 0 ? :decode_mcu_AC_first : :decode_mcu_AC_refine
      end
    else
      :decode_baseline
    end
  decode_fn = method(decode_fn)

  mcu = 0
  mcu_expected =
    if @components.size == 1
      @components[0].blocks_per_line * @components[0].blocks_per_column
    else
      @mcus_per_line * @mcus_per_column
    end
  @reset_interval ||= mcu_expected

  while mcu < mcu_expected
    @bit_io.reset!

    # reset interval stuff
    @components.each { |c| c.pred = 0 }
    @eobrun = 0

    if @components.size == 1
      component = @components[0]
      @reset_interval.times do
        decode_block(component, decode_fn, mcu)
        mcu += 1
      end
    else
      @reset_interval.times do
        @components.each do |c|
          c.v.times do |j|
            c.h.times do |k|
              decode_mcu(c, decode_fn, mcu, j, k)
            end
          end
        end
        mcu += 1

        # If we've reached our expected MCU's, stop decoding
        break if mcu == mcu_expected
      end
    end

    loop do
      marker = @bit_io.peek_bytes(2)
      case marker
      when "\xFF\xD0".."\xFF\xD7"
        # RSTx
        @bit_io.skip_bytes(2)
        break
      when "\xFF\x00"
        # stuffed 0
        @bit_io.skip_bytes(2)
      when "\xFF\xFF"
        # maybe a series of FF's followed by 0
        @bit_io.skip_bytes(1)
      when nil, ""
        # EOF?
        # return @offset
        break
      else
        warn "[?] expected RSTx, but got #{marker.inspect}"
        return @offset
      end
    end
  end # while

  @offset
end