Class: PDF::Reader::Filter
- Inherits:
-
Object
- Object
- PDF::Reader::Filter
- Defined in:
- lib/pdf/reader/filter.rb
Overview
Various parts of a PDF file can be passed through a filter before being stored to provide support for features like compression and encryption. This class is for decoding that content.
Instance Method Summary collapse
-
#ascii85(data) ⇒ Object
Decode the specified data using the Ascii85 algorithm.
-
#asciihex(data) ⇒ Object
Decode the specified data using the AsciiHex algorithm.
- #depredict(data, opts = {}) ⇒ Object
-
#filter(data) ⇒ Object
attempts to decode the specified data with the current filter.
-
#flate(data) ⇒ Object
Decode the specified data with the Zlib compression algorithm.
-
#initialize(name, options = nil) ⇒ Filter
constructor
creates a new filter for decoding content.
-
#lzw(data) ⇒ Object
Decode the specified data with the LZW compression algorithm.
- #png_depredict(data, opts = {}) ⇒ Object
-
#runlength(data) ⇒ Object
Decode the specified data with the RunLengthDecode compression algorithm.
- #tiff_depredict(data, opts = {}) ⇒ Object
Constructor Details
#initialize(name, options = nil) ⇒ Filter
creates a new filter for decoding content.
Filters that are only used to encode image data are accepted, but the data is returned untouched. At this stage PDF::Reader has no need to decode images.
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# File 'lib/pdf/reader/filter.rb', line 41 def initialize (name, = nil) @options = case name.to_sym when :ASCII85Decode then @filter = :ascii85 when :ASCIIHexDecode then @filter = :asciihex when :CCITTFaxDecode then @filter = nil when :DCTDecode then @filter = nil when :FlateDecode then @filter = :flate when :JBIG2Decode then @filter = nil when :JPXDecode then @filter = nil when :LZWDecode then @filter = :lzw when :RunLengthDecode then @filter = :runlength else raise UnsupportedFeatureError, "Unknown filter: #{name}" end end |
Instance Method Details
#ascii85(data) ⇒ Object
Decode the specified data using the Ascii85 algorithm. Relies on the AScii85 rubygem.
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# File 'lib/pdf/reader/filter.rb', line 75 def ascii85(data) data = "<~#{data}" unless data.to_s[0,2] == "<~" Ascii85::decode(data) rescue Exception => e # Oops, there was a problem decoding the stream raise MalformedPDFError, "Error occured while decoding an ASCII85 stream (#{e.class.to_s}: #{e.to_s})" end |
#asciihex(data) ⇒ Object
Decode the specified data using the AsciiHex algorithm.
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# File 'lib/pdf/reader/filter.rb', line 85 def asciihex(data) data.chop! if data[-1,1] == ">" data = data[1,data.size] if data[0,1] == "<" data.gsub!(/[^A-Fa-f0-9]/,"") data << "0" if data.size % 2 == 1 data.scan(/.{2}/).map { |s| s.hex.chr }.join("") rescue Exception => e # Oops, there was a problem decoding the stream raise MalformedPDFError, "Error occured while decoding an ASCIIHex stream (#{e.class.to_s}: #{e.to_s})" end |
#depredict(data, opts = {}) ⇒ Object
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# File 'lib/pdf/reader/filter.rb', line 158 def depredict(data, opts = {}) predictor = (opts || {})[:Predictor].to_i case predictor when 0, 1 then data when 2 then tiff_depredict(data, opts) when 10, 11, 12, 13, 14, 15 then png_depredict(data, opts) else raise MalformedPDFError, "Unrecognised predictor value (#{predictor})" end end |
#filter(data) ⇒ Object
attempts to decode the specified data with the current filter
Filters that are only used to encode image data are accepted, but the data is returned untouched. At this stage PDF::Reader has no need to decode images.
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# File 'lib/pdf/reader/filter.rb', line 64 def filter (data) # leave the data untouched if we don't support the required filter return data if @filter.nil? # decode the data self.send(@filter, data) end |
#flate(data) ⇒ Object
Decode the specified data with the Zlib compression algorithm
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# File 'lib/pdf/reader/filter.rb', line 97 def flate (data) deflated = nil begin deflated = Zlib::Inflate.new.inflate(data) rescue Zlib::DataError => e # by default, Ruby's Zlib assumes the data it's inflating # is RFC1951 deflated data, wrapped in a RFC1951 zlib container. # If that fails, then use an undocumented 'feature' to attempt to inflate # the data as a raw RFC1951 stream. # # See # - http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/243545 # - http://www.gzip.org/zlib/zlib_faq.html#faq38 deflated = Zlib::Inflate.new(-Zlib::MAX_WBITS).inflate(data) end depredict(deflated, @options) rescue Exception => e # Oops, there was a problem inflating the stream raise MalformedPDFError, "Error occured while inflating a compressed stream (#{e.class.to_s}: #{e.to_s})" end |
#lzw(data) ⇒ Object
Decode the specified data with the LZW compression algorithm
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# File 'lib/pdf/reader/filter.rb', line 119 def lzw(data) data = PDF::Reader::LZW.decode(data) depredict(data, @options) end |
#png_depredict(data, opts = {}) ⇒ Object
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# File 'lib/pdf/reader/filter.rb', line 199 def png_depredict(data, opts = {}) return data if opts.nil? || opts[:Predictor].to_i < 10 data = data.unpack("C*") pixel_bytes = opts[:Colors] || 1 scanline_length = (pixel_bytes * opts[:Columns]) + 1 row = 0 pixels = [] paeth, pa, pb, pc = nil until data.empty? do row_data = data.slice! 0, scanline_length filter = row_data.shift case filter when 0 # None when 1 # Sub row_data.each_with_index do |byte, index| left = index < pixel_bytes ? 0 : row_data[index - pixel_bytes] row_data[index] = (byte + left) % 256 #p [byte, left, row_data[index]] end when 2 # Up row_data.each_with_index do |byte, index| col = index / pixel_bytes upper = row == 0 ? 0 : pixels[row-1][col][index % pixel_bytes] row_data[index] = (upper + byte) % 256 end when 3 # Average row_data.each_with_index do |byte, index| col = index / pixel_bytes upper = row == 0 ? 0 : pixels[row-1][col][index % pixel_bytes] left = index < pixel_bytes ? 0 : row_data[index - pixel_bytes] row_data[index] = (byte + ((left + upper)/2).floor) % 256 end when 4 # Paeth left = upper = upper_left = nil row_data.each_with_index do |byte, index| col = index / pixel_bytes left = index < pixel_bytes ? 0 : row_data[index - pixel_bytes] if row.zero? upper = upper_left = 0 else upper = pixels[row-1][col][index % pixel_bytes] upper_left = col.zero? ? 0 : pixels[row-1][col-1][index % pixel_bytes] end p = left + upper - upper_left pa = (p - left).abs pb = (p - upper).abs pc = (p - upper_left).abs paeth = if pa <= pb && pa <= pc left elsif pb <= pc upper else upper_left end row_data[index] = (byte + paeth) % 256 end else raise ArgumentError, "Invalid filter algorithm #{filter}" end s = [] row_data.each_slice pixel_bytes do |slice| s << slice end pixels << s row += 1 end pixels.map { |bytes| bytes.flatten.pack("C*") }.join("") end |
#runlength(data) ⇒ Object
Decode the specified data with the RunLengthDecode compression algorithm
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# File 'lib/pdf/reader/filter.rb', line 125 def runlength(data) pos = 0 out = "" while pos < data.length if data.respond_to?(:getbyte) length = data.getbyte(pos) else length = data[pos] end pos += 1 case when length == 128 break when length < 128 # When the length is < 128, we copy the following length+1 bytes # literally. out << data[pos, length + 1] pos += length else # When the length is > 128, we copy the next byte (257 - length) # times; i.e., "\xFA\x00" ([250, 0]) will expand to # "\x00\x00\x00\x00\x00\x00\x00". out << data[pos, 1] * (257 - length) end pos += 1 end out end |
#tiff_depredict(data, opts = {}) ⇒ Object
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# File 'lib/pdf/reader/filter.rb', line 173 def tiff_depredict(data, opts = {}) data = data.unpack("C*") unfiltered = [] bpc = opts[:BitsPerComponent] || 8 pixel_bits = bpc * opts[:Colors] pixel_bytes = pixel_bits / 8 line_len = (pixel_bytes * opts[:Columns]) pos = 0 if bpc != 8 raise UnsupportedFeatureError, "TIFF predictor onlys supports 8 Bits Per Component" end until pos > data.size row_data = data[pos, line_len] row_data.each_with_index do |byte, index| left = index < pixel_bytes ? 0 : row_data[index - pixel_bytes] row_data[index] = (byte + left) % 256 end unfiltered += row_data pos += line_len end unfiltered.pack("C*") end |