VeryPDF JBIG2 Compression Engine
In its lossless mode JBIG2 can generate image files that are from 3 to 5 times smaller than the corresponding Group 4 Tiff images. The lossy mode of JBIG2 can compress to much higher levels without significant loss of image quality. Furthermore, by compressing across pages in a multi-page TIFF file, size reductions of 10-fold or more are achievable.
JBIG2 compression was incorporated into PDF specification starting from Acrobat 5. Most JBIG2 compressed images are embedded inside PDF files for easier viewing by the free Acrobat reader.here as a 1.12MB PDF file) has been published in 2000 as the international standard ITU T.88, and in 2001 as ISO/IEC 14492. The specification only deals with decoding JBIG2 images. Many aspects of the encoding were left open as implementation choices. Also, unlike the traditional codecs, such as TIFF or JPEG, there are several coding schemes and templates available to deal with a variety of pixel patterns.
The use of symbol dictionaries and symbol matching in JBIG2 enables very effective encoding of documents that contain recurring symbols, making JBIG2 ideal for compressing scanned documents. The compression process starts by segmenting a page into symbol classes and building symbol dictionaries through pattern matching and similarity analysis. The symbol dictionaries are stored in the document together with a content stream which encodes positional information for instances of a symbol. In lossy compressions, minor differences among symbols in a similarity class are thrown away. In lossless encoding, the minor differences are encoded as refinements.
The quality of the compressed JBIG2 image and the level of compression is largely determined by the choice of algorithms and heuristics that goes into the symbol classification and pattern matching. Every implementation of JBIG2 encoder will produce a different compressed file from the same input.
The use of JBIG2 compression was made popular by the inclusion of JBIG2 filters in Acrobat 5. Unfortunately, the Acrobat decoder cannot handle the full range of compression options envisioned in the JBIG2 specification.
VeryPDF JBIG2 encoder was written in portable C++ language and produces JBIG2 streams that are compatible with Adobe Acrobat. Certain advanced features (such as non-standard adaptive templates for arithmetic encoding) are not used in favor of maintaining this compatibility.
|JBIG2 Encoder Features:|
|Cross-platform object oriented C++ code|
|Creates both multi-page JBIG2 (*.jb2) and linearized PDF files|
|Compresses across pages in a multi-page document|
|Compresses in both lossless and lossy modes|
|Encodes from any file or stream|
For most applications, JBIG2 compressed images are embedded inside PDF documents and are decoded by the Acrobat viewer. VeryPDF JBIG2 decoder is integrated with VeryPDF PDF Library and can extract and decode JBIG2 image streams from PDF files. It is also possible to convert these streams to other formats, such as Fax Group 4. A potential application of the decoder is in the conversion of existing PDF files into PDF/A: the standardized subset of PDF specification suitable for long term archiving.
|JBIG2 Decoder Features:|
|Cross-platform object oriented C++ code|
|Can decode JBIG2 (*.jb2) files and PDF streams|
|Can generate both sequential and random JBIG2 files|
|Arithmetic, Huffman and MMR decoders|
|Can decode Generic, Text and Halftone regions|
|Supports standard and user defined Huffman tables|
|Supports standard and user defined adaptive templates|
|Supports symbol refinement|
documents are typically 10 times smaller than the corresponding
multi-page TIFF G4 image files. Batch conversion of existing TIFF
files to JBIG2 compressed documents can restore about 90% of used
storage. In addition to saving on storage costs, smaller files are
also easier and faster to distribute, backup or archive.
Smaller files are
faster to download. A JBIG2 compressed document can be downloaded
about 10 times faster than the corresponding TIFF file. Also, if a
JBIG2 file is embedded inside a inearized PDF document, then the
document will be further optimized for on-line viewing. The Acrobat
viewer can open such documents in streaming mode, downloading only
the parts that are required to view each page. For linearized PDF
documents, the time to view each page becomes independent of the
number of pages in the document.
Businesses that are document centric, such as legal or insurance companies, deal with large number of electronic files. Many of these documents are scanned into multi-page TIFF files. A typical TIFF file of a few hundred pages is several mega-bytes large. These large files are inherently insecure and difficult to distribute through publishing on the Web or via e-mail. Many e-mail accounts have limitations on attachment sizes and will bounce back e-mails that exceed their limits. Also, there is no universal platform agnostic viewer for TIFF images. JBIG2 technology provides a mechanism for overcoming these problems. It converts the TIFF file into a standard compressed, secured and web-optimized PDF document suitable for publication and firstname.lastname@example.org.
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