What is JBIG2? An Introduction to JBIG2

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What is JBIG2?

JBIG2 is a relatively new image compression standard that was first published as an international standard in 2000. It was a modern option for both lossless and lossy image compression. The standard is designed to compress images better than the traditional JBIG and Fax Group 4 standards previously implemented for bi-level or black and white images. JBIG2 compression reduces files to as small as one fifth of the size of pictures saved under traditional formats. When black and white images are compressed with the JBIG2 algorithm, compression ratios can be 100:1 when compared to traditional TIFF image formats.

What Type of Imagery is Suitable for the JBIG2 Compression Standard?

JBIG2 compression is primarily used for black and white imagery. This is because the algorithm relies on symbol recognition to get a high degree of file compression. The compression algorithm scans image files for similarly arranged shapes, it then uses associated symbols to find similarities within the image. Industry now finds the algorithm useful for scanning and storing black and white documents for archival purposes, as a significant amount of space is saved in comparison to traditional file formats.

What Are the Steps of JBIG2 Compression?

Step 1 – The compression algorithm identifies the connected components in the image (normally four or eight are found per image).

Step 2 – The algorithm then places components in a “similarity” class that uses an image template as a representative, with the location of each instance being recorded.

Step 3 – The image templates, index, and location are then compressed and written to a file. The compression uses an arithmetic coding with Huffmann or arithmetic encoding on the image file’s location information.

File Size

The file size advantage of JBIG2s over generic TIFFs is usually quite dramatic. For a typical scanned document at 300dpi, the TIFF is roughly 75 KB -125 KB bytes per image, while the JBIG2 is about 5x-10x smaller, in the range of 10 KB -15KB bytes per image.

The compressed JBIG2 file size can differ dramatically between different JBIG2 encoders. For example, consider an original TIFF file. The jb2-pdf file created by VeryDOC PDF Compressor is less than half the size of the one created by a competing vendor. Other file size comparisons between these two JBIG2 converters across several datasets are given here below. As shown, the VeryPDF encoded files are generally 35% - 40% smaller.

JBIG2-Compressed PDF Documents

The Adobe PDF document format has, until the release of the PDF 1.4 specifications, supported the standard compression/decompression filters: LZWDecode, FlateDecode, RunLengthDecode, CCITTFaxDecode, and DCTDecode (JPEG-based). These decoding filters allow the PDF data streams to be compressed when the PDF file is written and then decoded by the Adobe PDF Reader. With the inclusion of the JBIG2Decode filter in the PDF specifications in 2001 (see the PDF Reference, 3rd Edition, Version 1.4), scanned documents can now be encoded using the new ITU-approved JBIG2 format and, at the same time, be fully PDF-compliant.

When a new format is introduced, like JBIG2, JPEG2000, or MPEG4, there is usually a considerable time delay until supporting viewers/players and other editing software is available to handle documents in this new format. One advantage to PDF wrapping a new format like JBIG2 is that readability is essentially guaranteed, assuming a more recent version of Adobe Reader (5.05 or higher) has been installed on the client machine. In fact, most companies currently using JBIG2 for their document compression are using PDF-wrapped JBIG2, not native JBIG2. For a slight increase in file size, a JBIG2 document can be wrapped in a PDF, thereby enabling the document to access a range of features supported in PDF that are not available in native JBIG2.

References:

PDF/A: PDF Designed for Archival
The PDF/A-1b standard (ISO 19005-1:2005) is a subset of the PDF standard, designed for long-term archival of documents.

PDF Standards and Your Business

PDF/A: PDF for Archving

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