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# coding: utf-8
# typed: strict
# frozen_string_literal: true
class PDF::Reader
module Filter # :nodoc:
# some filter implementations support preprocessing of the data to
# improve compression
class Depredict
#: (?Hash[untyped, untyped]) -> void
def initialize(options = {})
@options = options
end
################################################################################
# Streams can be preprocessed to improve compression. This reverses the
# preprocessing
#
#: (String) -> String
def filter(data)
predictor = @options[:Predictor].to_i
case predictor
when 0, 1 then
data
when 2 then
tiff_depredict(data)
when 10, 11, 12, 13, 14, 15 then
png_depredict(data)
else
raise MalformedPDFError, "Unrecognised predictor value (#{predictor})"
end
end
private
################################################################################
#: (untyped) -> String
def tiff_depredict(data)
data = data.unpack("C*")
unfiltered = ''
bpc = @options[:BitsPerComponent] || 8
pixel_bits = bpc * @options[:Colors]
pixel_bytes = pixel_bits / 8
line_len = (pixel_bytes * @options[: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.pack("C*")
pos += line_len
end
unfiltered
end
################################################################################
#: (untyped) -> String
def png_depredict(data)
return data if @options[:Predictor].to_i < 10
data = data.unpack("C*")
pixel_bytes = @options[:Colors] || 1
scanline_length = (pixel_bytes * @options[:Columns]) + 1
row = 0
pixels = []
paeth, pa, pb, pc = 0, 0, 0, 0
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 = 0
row_data.each_with_index do |byte, index|
col = index / pixel_bytes
left = index < pixel_bytes ? 0 : Integer(row_data[index - pixel_bytes])
if row.zero?
upper = upper_left = 0
else
upper = Integer(pixels[row-1][col][index % pixel_bytes])
upper_left = col.zero? ? 0 :
Integer(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 MalformedPDFError, "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
end
end
end
|
