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Sample Ruby code for using PDFTron SDK to recompress bitonal (black and white) images in existing PDF documents using JBIG2 compression (lossless or lossy). The sample is intended to show how to specify hint information for the image encoder and is not meant to be a generic PDF optimization tool. To demonstrate the possible compression rates, we recompressed a document containing 17 scanned pages. The original input document is ~1.4MB and is using standard CCITT Fax compression. Lossless JBIG2 compression shrunk the filesize to 641KB, while lossy JBIG2 compression shrunk it to 176KB. Learn more about our Ruby PDF Library.
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#---------------------------------------------------------------------------------------
# Copyright (c) 2001-2022 by PDFTron Systems Inc. All Rights Reserved.
# Consult LICENSE.txt regarding license information.
#---------------------------------------------------------------------------------------
require '../../../PDFNetC/Lib/PDFNetRuby'
include PDFNetRuby
require '../../LicenseKey/RUBY/LicenseKey'
$stdout.sync = true
# This sample project illustrates how to recompress bi-tonal images in an
# existing PDF document using JBIG2 compression. The sample is not intended
# to be a generic PDF optimization tool.
#
# You can download the entire document using the following link:
# http://www.pdftron.com/net/samplecode/data/US061222892.pdf
PDFNet.Initialize(PDFTronLicense.Key)
pdf_doc = PDFDoc.new("../../TestFiles/US061222892-a.pdf")
pdf_doc.InitSecurityHandler
cos_doc = pdf_doc.GetSDFDoc
num_objs = cos_doc.XRefSize
i = 1
while i < num_objs do
obj = cos_doc.GetObj(i)
if !obj.nil? and !obj.IsFree and obj.IsStream
# Process only images
itr = obj.Find("Subtype")
if !itr.HasNext or !itr.Value.GetName == "Image"
i = i + 1
next
end
input_image = Image.new(obj)
# Process only gray-scale images
if input_image.GetComponentNum != 1
i = i + 1
next
end
# Skip images that are already compressed using JBIG2
itr = obj.Find("Filter")
if itr.HasNext and itr.Value.IsName and itr.Value.GetName == "JBIG2Decode"
i = i + 1
next
end
filter = obj.GetDecodedStream
reader = FilterReader.new(filter)
hint_set = ObjSet.new # hint to image encoder to use JBIG2 compression
hint = hint_set.CreateArray
hint.PushBackName("JBIG2")
hint.PushBackName("Lossless")
new_image = Image.Create(cos_doc, reader,
input_image.GetImageWidth,
input_image.GetImageHeight,
1,
ColorSpace.CreateDeviceGray,
hint)
new_img_obj = new_image.GetSDFObj
itr = obj.Find("Decode")
if itr.HasNext
new_img_obj.Put("Decode", itr.Value)
end
itr = obj.Find("ImageMask")
if itr.HasNext
new_img_obj.Put("ImageMask", itr.Value)
end
itr = obj.Find("Mask")
if itr.HasNext
new_img_obj.Put("Mask", itr.Value)
end
cos_doc.Swap(i, new_img_obj.GetObjNum)
end
i = i + 1
end
pdf_doc.Save("../../TestFiles/Output/US061222892_JBIG2.pdf", SDFDoc::E_remove_unused)
pdf_doc.Close
PDFNet.Terminate
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